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In the .NET Framework, the classes available from the System.IO namespace provide for both synchronous and asynchronous read write operations on two distinct categories of data streams and files. A file is an ordered and named collection of bytes and is persistently stored to a disk. A stream represents a block of bytes that is read from, and written to, a data store. The data store can be based on a variety of storage media, including memory, disk files, and remote URLs. A stream is a kind of superset of a file, or in other words, a file that can be saved to a variety of storage media including memory. To work with streams, the .NET Framework defines several flavors of reader and writer classes. Figure 1-1 shows how each class relates to the others. Figure 1-1 Streams can be read and written using made-to-measure reader and writer classes. In the .NET Framework, base reader and writer classes find a number of concrete implementations, including StreamReader and StringReader and their...
The .NET Framework ships with a variety of reader and writer classes that help you work with data more complicated than simple byte streams. Readers and writers encapsulate a stream and provide a translation layer that turns values into their byte stream equivalents (for writers) and vice versa (for readers). Reader and writer classes in .NET are typically named to reflect the type of formatting that they perform. For example, the HtmlTextWriter class writes values destined for HTTP response information sent by ASP.NET, while the StringReader class reads values written using their string representation. The writer and reader classes also handle varying encoding schemes, which is not possible using lower-level stream objects. The classes derived from the abstract TextWriter class, for example, enable your C code to write text and have it encoded in the stream using ASCII, Unicode, UTF7, or UTF8 encoding algorithms.
In the .NET Framework, the XML DOM classes make intensive use of streaming readers and writers to build the in-memory tree and to flush it out to disk. Thus, readers and writers are definitely the only XML primitives available in the .NET Framework. Consequently, to build up a sort of lightweight XML DOM parser, we can only rely, once more, on readers and writers. You will use a normal XML (validating) reader to visit the nodes in sequence. While reading, however, you are given the opportunity to change attribute values and node contents. Unlike the XML DOM, changes will have immediate effect. How can you obtain these results The idea is to use an XML writer on top of the reader. You use the reader to read each node in the source document and an underlying writer to create a hidden copy of it. In the copy, you can add some new nodes and ignore or edit some others. When you have finished, you simply replace the old document with the new one. You can decide to write the copy in memory...
As mentioned, XML text writers do not validate against schema or DTD files. In fact, writing the XML document and validating its contents are two distinct operations that can't occur at the same time. However, if you need to make sure that the document just written is valid against, say, a schema, you can proceed in the following way write the document and, when finished, validate it using a validating reader. Sounds straightforward Well, it isn't. The difficulty lies in the fact that, to validate, you must reread the text just written. If you are using a file, you can simply open the file using an XML reader and then instantiate a validating reader. The task is trickier if you happen to use an output stream in many cases, you can't read the contents of an output (and mostly write-only) stream. In this case, a possible workaround is caching the entire XML document into a string. When you've finished, you simply pass the XML fragment to the validating reader. If all went fine, you...
Let's review three examples of how the XmlTextReadWriter class can be used to modify XML documents without using the full-blown XML DOM. Looking at the source code, you'll realize that a read write streaming parser is mostly achieved by a smart and combined use of readers and writers.
StringWriter and StringReader both inherit from TextWriter and TextReader, respectively therefore they function the same way as other Readers and Writers.The crucial difference is that rather than using a Stream as the source it uses a String. A constructor for a typical StringReader is as follows StringWriter writer new StringWriter() doc.Save(writer) to StringWriter String strXML writer.ToString() to String Console.WriteLine(strXML)
In the .NET Framework, a writer class is merely a document-producer object. It exposes ad hoc methods to let developers create the desired output using highlevel tools. A method named WriteSchema that internally handles primitives to add nodes and attributes is much more understandable than, say, a StringBuilder object that you use to build markup text. An XML writer is just a specialized writer that handles XML text. You can certainly design your own writer classes to quickly and easily enable developers to create certain compound documents. In doing so, though, you don't need to inherit from XmlWriter, XmlTextWriter, or BinaryWriter. Although you can, and often must, use those objects internally, the user-level interface should comprehend methods and properties that reflect the nature and the structure of the final document. As a general guideline, try to provide constructors that work over streams and text writers and to provide as many overloads as you can. For example, the...
Suppose you wanted to know if any changes had occurred since you acquired and released a reader lock. One way to determine this is to use the WriterSeqNum property of the ReaderWriterLock object. This property returns a value that can be used with the AnyWritersSince method to determine if any writer locks have been released since WriterSeqNum was acquired. Listing 9.12 WriterSeqNum can be used to see if data has changed (VB.NET). Public Sub Bid(ByVal Amount As Decimal, ByVal BiddersName As String) Dim WriterSeqNum As Integer Retrieve the writer sequence number and save it Look for new writers If (Amount TheCurrentPrice) Then WriterSeqNum ItemLock.WriterSeqNum ItemLock.ReleaseReaderLock() Thread.Sleep(1000) ' Make the changes more obvious If Then If (Amount TheCurrentPrice) Then TheCurrentPrice Amount TheBiddersName BiddersName Else In listing 9.12 we first acquire a reader lock. To simplify the code we wait indefinitely for the lock. Once the reader lock is acquired we retrieve the...
The Java strategy for Readers and Writers is to have a lot of different classes that specialize. C uses fewer classes that allow specialized behavior to be chosen through the constructors. StreamReader has 10 constructors that determine the source (file or stream), buffer size, character encoding, and whether it allows mark detection. Let's try obtaining a StreamReader using one of these constructors
An XML writer represents a component that provides a fast, forward-only way of outputting XML data to streams or files. More important, an XML writer guarantees by design that all the XML data it produces conforms to the W3C XML 1.0 and Namespace recommendations. Let's rewrite our sample file using .NET XML writers, as shown in the following code. A .NET XML writer features ad hoc write methods for each possible XML node type and makes the creation of XML output more logical and much less dependent on the intricacies, and even the quirkiness, of the markup languages. Open the XML writer (default encoding charset) XmlTextWriter xmlw new XmlTextWriter(filename, null) xmlw.Formatting Formatting.Indented Close the writer xmlw.Close() An XML writer is a specialized class that knows only how to write XML data to a variety of storage media. It features ad hoc methods to write any special item that characterizes XML documents from character entities to processing instructions, from comments...
Immediately after class initialization, the reader and the writer are configured to work properly. This process entails setting the policy for white spaces and setting the formatting options, as shown here I recommend that you configure the reader to ignore any white space so that it never returns any white space as a distinct node. This setting is correlated to the autoformatting feature you might need on the writer. If the reader returns white spaces as nodes and the writer indents any node being created, the use of the writer's WriteNode method can cause double formatting.
Private BinaryWriter Writer private FileStream BinaryFile Writer new BinaryWriter(BinaryFile) Writer.Write('a') Writer.Write(123) Writer.Write(456.7 8 9) Writer.Write( test string ) The code in Listing 25-4 is structured with a class design similar to the design in Listing 25-3. The code contains a MainClass and a FileTestClass. The constructor of the FileTestClass class in Listing 25-4 creates a file stream and then creates a BinaryWriter object. A reference to the file stream is passed to the constructor of the BinaryWriter object, which sets up the relationship between the binary writer and the stream to which it writes its data. In Listing 254, all data written to the binary writer eventually makes its way to the file stream set up in the constructor. The WriteBinaryData() method writes a character, an integer, a double, and a string to the underlying stream. The BinaryWriter class implements several overloads of a method named Write(). The Write() method overloads support the...
Closes both the writer and the underlying stream. The writer can't be used to write additional text. Any attempt would cause an invalid operation exception to be thrown. Flushes whatever is in the buffer to the underlying streams and also flushes the underlying stream. After this method is called, the writer remains active and ready to write more to the same stream. An XML writer accumulates text in an internal buffer. Normally, the buffer is flushed, and the XML text actually written, only when the writer is closed. By calling the Flush method, however, you can empty the buffer and write the current contents down to the stream. Some working memory is freed, the writer is not closed, and the operation can continue. For example, let's assume that you use a file as the output stream. At some point, while generating the XML content, you call Flush. As a result, the file (existing or already created by the time Flush is called) is partially populated. However, it can't be accessed by...
I designed the XmlTextReadWriter class with a minimal programming interface because, in most cases, what you really need is to combine the features of the reader and the writer to create a new and application-specific behavior such as updating a particular attribute on a certain node, deleting nodes according to criteria, or adding new trees of nodes. The class provides the methods listed in Table 4-9. Specialized version of the writer's WriteAttributes method. Writes out all the attributes for the specified node, taking into account all the changes cached through the AddAttributeChange method. Terminates the current document in the writer and closes both the reader and the writer. Prepares the internal writer to output the document and adds default comment text and the standard XML prolog. A read write XML document is processed between two calls to WriteStartDocument and WriteEndDocument, shown in the following code. The former method initializes the underlying writer and writes a...
KFJU Tort Writer flu J Rrodof Jfc f* KFJU Tort Writer flu J Rrodof Jfc f* After you've set up the class and collection, create an interface with text boxes for the user input of elements and values, like that shown in Figure 18.8. The Add button will be used to add an element-value pair to the collection, and the XML Text Writer button will be used to generate the relevant XML document. Run the project and enter some element-value pairs, clicking Add each time. Next, click the XML Text Writer button. You'll find that an XML document containing the elements and values you added has been created. It will look something like this
As we've seen, an XML writer is a .NET Framework class that specializes in writing out XML text. Because there is just one flavor of XML, the need for customized versions of XmlTextWriter is extremely low. However, a lot of documents and objects out there might take significant advantage of an ad hoc, specialized, and seamless XML serialization class. In the .NET Framework, all the XML files being used from ADO.NET DiffGram objects to Web .config files are written using XML writers. (ADO.NET DataSet objects are always remoted and serialized in a special XML format called the DiffGram see Chapter 10.) In addition, the XML serializer saves and restores .NET Framework objects to and from XML documents. (I'll cover XML serialization in Chapter 11) So the .NET Framework provides you with some tools to save existing objects into an XML layout. The XML serializer is designed to map living instances of objects to an XML schema. Sometimes, though, you just need to produce a particular XML...
Read-only property that gets the state of the writer. The state can be any value taken from the WriteState enumeration and describes the element being written. In general, the XmlWriter class properties serve to track the state in which another component might have left the writer. Note that these properties belong to the current instance of the writer object. If you are using the same writer to generate more documents on the same stream, these properties are not automatically reset when you start a new document.
Close() Closes the writer and frees any associated resources. In the process, the buffer is Flush() Clears all buffers for the current writer and causes any buffered data to be written to the underlying device, but does not close the writer. NewLine Indicates the newline constant for the derived writer class. The default line
The final writer reader sets you will examine here are BinaryReader and BinaryWriter, both of which derive directly from System.Object. These types allow you to read and write discrete data types to an underlying stream in a compact binary format. The BinaryWriter class defines a highly overloaded Write() method to place a data type in the underlying stream. In addition to Write(), BinaryWriter provides additional members that allow you to get or set the internal Stream-derived type and offers support for random access to the data (see Table 20-10).
XmlReader has a complementary, stream-based writer class that meets this need. Predictably, it's called XmlWriter. Like XmlReader, XmlWriter offers a lean-and-mean technique for the efficient writing of documents using a stream model. It also shares the problems inherent in that model - chiefly, the lack of random access, the absence of enduring context, and no intrinsic mechanism to contain the document in memory.
Although powerful and considerably feature-rich, an XML writer is not perfect it still leaves some margin for errors. To be more precise, the XmlWriter class certainly generates 100-percent well-formed code, but only if you pass on correct information. In particular, an XML writer does not check for invalid characters in element and attribute names. It also does not guarantee that any Unicode characters you use fit into the current encoding schema. As a consequence, any characters outside the encoding schema are not escaped into character entities and might lead to incorrect output. An XML writer also does not verify duplicate attributes it simply dumps the text out when you call the appropriate method. Nor does an XML writer validate any identifiers (for example, the SYSTEM identifier) you specify when you create a DOCTYPE node. In addition, the XmlWriter class does not validate against any schema or document type definition (DTD). Creating a validating writer is not difficult,...
The System.Threading.ReaderWriterLockSlim class provides a convenient implementation of reader-writer locking that takes care of managing the locks. This class is a lightweight alternative for the create the reader-writer lock When you press the Enter key, the main application thread acquires the write lock, which is held for two seconds and then released. You can see from the following results that once the write lock has been requested, the number of Tasks holding the read lock starts to drop. This is because calls to EnterReadLock() will now wait until the writer lock has been released to ensure writer exclusivity.
The XmlRecordsetWriter class embeds an instance of the XmlTextWriter class but does not inherit from it. All the hard work of creating the XML output is accomplished through the internal writer, but the class programming interface is completely customized and largely simplified. protected XmlTextWriter Writer Writer new XmlTextWriter(filename, null) SetupWriter() Writer new XmlTextWriter(s, null) SetupWriter() Writer new XmlTextWriter(tw) SetupWriter() Ensures that all the pending nodes are closed and releases the underlying writer and stream. WriteRecordset For writing sch mas and content, the XmlRecordsetWriter class needs to read information out of some ADO.NET objects. For this reason, methods like WriteSchema, WriteContent, and WriteRecordset have the following four overloads
XmlWriter is an abstract class with, at present, one predefined derived class XmlTextWriter. Despite its name, this class can write to more than just text files. It is named as it is because it writes text, but that text can be sent to any sort of stream, as will become apparent when we examine the class constructors. Since this is the only implementation of XmlWriter that can be instantiated in the current release of the .NET Framework, the two classes are very close in terms of their interfaces. We'll be practical, then, and discuss XML writers by exploring the details of XmlTextWriter. Eventually, we'll use XmlTextWriter to extend our XMLCategorizer example with server-side log files. Before we can do that, though, we'll take a formal look at the public interface of this class. The first task in working with a writer is of course to create an instance of it, so the first stop on the tour of XmlTextWriter must examine its constructors.
XmlTextWriter writer new XmlTextWriter( test.xml , new System.Text.ASCIIEncoding( )) writer.Formatting Formatting.Indented writer.Indentation 4 writer.WriteStartDocument( ) writer.WriteComment( Comment ) writer.WriteStartElement( ElementName , myns ) writer.WriteStartAttribute( prefix , attrName , myns ) writer.WriteEndAttribute( ) myns , value ) writer.WriteEndElement( ) writer.WriteEndDocument( ) writer.Flush( ) writer.Close( )
Table 4-2 summarizes the allowable states for an XML writer. Values come from the WriteState enumeration type. Any XML writer is expected to properly and promptly update its WriteState property as various internal operations take place. Table 4-2 States of an XML Writer Table 4-2 States of an XML Writer The writer enters this state when an attribute is being written. Table 4-2 States of an XML Writer The Close method has been called, and the writer is no longer available for writing operations. The writer enters this state when the contents of a node is being written. The writer enters this state when an element start tag is being written. The writer is writing the prolog (the section that declares the element names, attributes, and construction rules of valid markup for a data type) of a well-formed XML 1.0 document. The writer is in an initial state, waiting for a write call to be issued. When you create a writer, its state is set to Start, meaning that you are still configuring the...
Streams support data access at the byte level. They include methods called Read() and Write(), which work with an array of bytes that are processed during the call. However, working at the byte level might not be ideal for your application. Suppose, for example, that your application needs to write a series of integers to a stream. Because integers in the 32-bit implementation are four bytes wide, your C code would need to translate each integer into a string of four bytes that could be used in a call to the stream's implementation of Write(). The .NET Framework includes writer classes that support writing various higher-level data types to a stream. A writer might support many overloads of a Write() method. For example, a write can accept such data types as int, long, or double. The writer class implementations translate the data type into a series of bytes and pass that translated byte stream to a Stream object. This class design frees your code from having to deal with streams at...
9.2 Acquiring a writer lock from a ReaderWriterLock 166 This chapter uses a simulated auction to demonstrate this concept. To test our synchronization system we can utilize multiple threads. Each thread will have a list of items it is instructed to acquire, along with an allotment of bidding points. Since an auction involves many reads to data and a few writes, it is ideal for demonstrating the concepts of a reader writer lock.
Richard Anderson is an experienced software engineer and writer who spends his time working with Microsoft technologies, day in day out. Having spent the better part of a decade doing this, he is still remarkably sane Richard currently works for BMS software - an ADP company - where he is a technical architecture manager. Richard is currently working on the development of a large-scale Internet-based payroll and HR system.
This book explores the array of XML tools provided by the .NET Framework. XML is everywhere in the .NET Framework, from remoting to Web services, and from data access to configuration. In the first part of this book, you'll find in-depth coverage of the key classes that implement XML in the .NET platform. Readers and writers, validation, and schemas are discussed with samples and reference information. Next the book moves on to XPath and XSL Transformations (XSLT) and the .NET version of the XML Document Object Model (XML DOM).
DIANNE SIEBOLD is a software developer and writer specializing in VB, C , .NET Framework, WCF, ADO, and SQL Server. She has worked for a number of Microsoft partners writing enterprise applications with an emphasis on services and data access. Currently, she works for Microsoft writing developer documentation in the Dynamics product group. Reach her by e-mail at dsiebold earthlink.net.
Denise has worked in the computer industry since 1994 in a variety of roles ranging from Systems Engineer, Programmer, IS Manager, and Senior Consultant. Denise is also an avid writer, and has co-authored the following books MSDE Bible (IDG Books), Professional SQL Server 2000 XML (Wrox Press), and Professional .NETFramework (Wrox Press).
The first difference between MSXML and .NET Framework XML core classes that catches the eye is the fact that while MSXML supports XMLDOM and SAX parsers, the .NET Framework supplies an XMLDOM parser and XML readers and writers. (More on readers shortly.) This is just the most remarkable example of a common pattern, however. Quite a few key features of MSXML are apparently not supported in the .NET Framework XML core classes, but this hardly results in a loss of programming power.
As mentioned, along with XML readers and writers, the .NET Framework also provides classes that load and edit XML documents according to the W3C DOM Level 1 and Level 2 Core. The key XMLDOM class in the .NET Framework is XmlDocument not much different from the DOMDocument class, which you might recognize from working with MSXML. The XMLDOM representation of an XML document is fully editable. Attributes and text can be randomly accessed, and nodes can be added and removed. You perform updates on a loaded XMLDOM document by first creating a node object (the XmlNode class) and then binding it to the existing tree. All in all, the underlying writing pattern is close to that of XML writers you write nodes to the stream in one case, and you add nodes to the tree in the other. Of course, if you are using the XMLDOM, bear in mind that all changes occur in memory and must be flushed to the storage medium prior to return. (The XMLDOM API is described in detail in Chapter 5.)
A good example of a commitment to quality is when I had my first monthly review at NuMega. First off, I was astounded that I was getting a review that quickly when normally you have to beg for any feedback from your managers. One of the key parts of the review was to record how many bugs I had logged against the product. I was stunned to discover that NuMega would evaluate this statistic as part of my performance review, however, because even though tracking bugs is a vital part of maintaining a product's quality, no other company I had worked at had ever checked something so obvious. The developers know where the bugs are, but they must be given an incentive to enter those bugs into the bug tracking system. NuMega found the trick. When I learned about the bug count entry part of my review, you'd better believe I logged everything I found, no matter how trivial. With all the technical writers, quality engineers, development engineers, and managers engaged in healthy competition to log...
As mentioned earlier, managed modules contain both metadata and intermediate language (IL). IL is a CPU-independent machine language created by Microsoft after consultation with several external commercial and academic language compiler writers. IL is much higher level than most CPU machine languages. IL understands object types and has instructions that create and initialize objects, call virtual methods on objects, and manipulate array elements directly. It even has instructions that throw and catch exceptions for error handling. You can think of IL as an object-oriented machine language.
When porting a .NET application from a console application to a Windows application, you will notice that the familiar format of the Con-sole.WriteLine method is not reflected in standard string handling. It is, however, available in StringBuilder.AppendFormat and Stream-Writer.WriteLine.
The .NET Framework class libraries are monumentally important to providing language interoperability because they allow developers to use a single programming interface to all the functionality exposed by the CLR. If you've ever used more than one dissimilar language in development for Windows, you'll love this feature. In fact, the .NET Framework class libraries are forging a revolutionary trend in compiler development. Before .NET, most compiler writers developed a language with the ability to do most of its own work. Even a language such as C++, which was designed as a scaled-down grouping of functionality to be used in conjunction with a class library, has at least some functionality on its own. However, in the world of .NET, languages are becoming little more than syntactical interfaces to the .NET Framework class libraries.
To make it easy for language writers to port their languages to .NET, Microsoft developed a language akin to assembly language called Microsoft intermediate language (MSIL). To compile applications for .NET, compilers take source code as input and produce MSIL as output. MSIL itself is a complete language that you can write applications in. However, as with assembly language, you would probably never do so except in unusual circumstances. Because MSIL is its own language, each compiler team makes its own decision about how much of the MSIL it will support. However, if you're a compiler writer and you want to create a language that does interoperate with other languages, you should restrict yourself to features specified by the CLS.
The Common Language Specification (CLS) defines a range of types and language features (such as exception handling) that must be supported by a language if it is to work within the .NET world. As such, the CLS concerns compiler writers far more than it does developers, but there's one detail that needs to be noted about it.
CMSs try to separate the content from how it is displayed. This will allow a writer to hone her craft and let designers do what they do best, which of course is Web site design. This benefit allows a Web site to hire the best writers and not just the best writers who know HTML.
XML readers and writers work in separate compartments and in an extremely specialized way. Readers just read, and writers just write. There is no way to force things to go differently, and in fact, the underlying streams are read-only or write-only as required. Suppose that your application manages lengthy XML documents that contain rather volatile data. Readers provide a powerful and effective way to read that contents. Writers, on the other hand, offer a fantastic tool to create that document from scratch. But if you want to read and write the document at the same time, you must necessarily resort to a full-fledged XML Document Object Model (XML DOM). What can you do to read and write an XML document without loading it entirely into memory In Chapter 5, I'll tackle the XML DOM model of a parser, which is the classic tool for performing read write operations on an XML tree. The strength of the XML DOM parsers, but also their greatest drawback, lies in the fact that an XML DOM parser...
User-mode debuggers are much more familiar to most developers. Not surprisingly, usermode debuggers are for debugging user-mode applications. The Microsoft Visual Studio .NET debugger is a prime example of a user-mode debugger. Kernel-mode debuggers, as the names implies, let you debug the operating system kernel. These debuggers are used mostly by device driver writers when they're debugging their device drivers.
A goal of .NET is to support language integration in such a way that programs can be written in any language, yet can interoperate with one another, taking full advantage of inheritance, polymorphism, exceptions, and other features. However, languages are not made equal because one language may support a feature that is totally different from another language. For example, Managed C++ is case-sensitive, and VB.NET is not. In order to bring everyone to the same sheet of music, Microsoft has published the Common Language Specification (CLS). The CLS specifies a series of basic rules that are required for language integration. Since Microsoft provides the CLS that spells out the minimum requirements for being a .NET language, compiler vendors can build their compilers to the specification and provide languages that target .NET. Besides compiler writers, application developers should read the CLS and use its rules to guarantee language interoperation. 10 Search MSDN Online for Collected...
Our sample application intentionally follows a more sophisticated approach to display formatted output in the text box. In addition, this code turns out to be a useful exercise for understanding the logic of XML writers. If you want to generate XML output in the .NET Framework, unless the text is short and straightforward, you have no good reason for not using XML writers. Using XML writers also provides automatic and free indentation. Don't think that choosing an XML writer ties you to using a specific output stream. As the following code demonstrates, the output of an XML writer can be easily redirected to a string Create a string writer to hold the XML text. For efficiency, the string writer is based on a StringBuilder object. StringBuilder sb new StringBuilder( ) StringWriter sw new StringWriter(sb) Instantiate the XML writer XmlTextWriter writer new XmlTextWriter(sw) writer.Formatting Formatting.Indented writer.WriteStartElement( results ) LoopThroughChildren(writer, n) Complete...
To send and receive data, the TcpClient provides a GetStream method. The method returns a NetworkStream object. You can use this stream to read and write to the network socket. To use the stream the method returns, assign the stream to a variable of type Stream, defined in the System.IO namespace. You can then use this variable to create stream readers and writers to send and receive information over the network socket. For more information on reading or writing from a stream, see the sections Read from a Stream or Write to a Stream.
As mentioned, configuration files are standard XML files that follow a particular schema. This schema defines all possible configuration settings for machine, security, and application configuration files. The .NET Framework provides you with ad hoc classes to read configuration settings, but no writing can be performed. You need to be familiar with XML readers and writers if you want to directly edit the configuration files. (In light of this, bear in mind that XML elements and attribute names are case-sensitive.) All the configuration files are rooted in the element. Table 15-1 lists the first-level children of the element. Each node has a specified number of child elements that provide a full description of the setting. For example, the element optionally contains the tag, in which you can store information about the users who can safely access the URL resources.
The term serialization describes the process of persisting (and possibly transferring) the state of an object to a stream. The persisted data sequence contains all necessary information needed to reconstruct (or deserialize) the state of the object for use later. Using this technology, it is trivial to save vast amounts of data (in various formats) with minimal fuss and bother. In fact, in many cases, saving application data using serialization services is much less cumbersome than making direct use of the readers writers found within the System.IO namespace.
Now that you have a better handle on the use of various readers and writers, next you'll look at the role of the FileSystemWatcher class. This type can be quite helpful when you wish to programmatically monitor (or watch ) files on your system. Specifically, the FileSystemWatcher type can be instructed to monitor files for any of the actions specified by the NotifyFilters enumeration (while many of these members are self-explanatory, check the .NET Framework 3.5 SDK documentation for further details)
Writer.WriteStartDocument() Writer.WriteComment( Created by XmlRecordsetWriter ) Writer.WriteStartElement( xml ) Writer.WriteAttributeString( xmlns , s , null, uuid BDC6E3F0-6DA3-11d1-A2A3-0 0AA0 0C14 8 82 ) Writer.WriteAttributeString( xmlns , dt , null, uuid C2F41010-65B3-11d1-A2 9F-00AA00C14 8 82 ) Writer.WriteAttributeString( xmlns , rs , null, urn schemas-microsoft-com rowset ) Writer.WriteAttributeString( xmlns , z , null, RowsetSchema ) Writer.WriteStartElement( s , Schema , null) Writer.WriteAttributeString( id , RowsetSchema ) Writer.WriteStartElement( s , ElementType , null) Writer.WriteAttributeString( name , row ) Writer.WriteAttributeString( content , eltOnly ) Write the column info based on the table passed int index 0 Writer.WriteStartElement( s , AttributeType , null) Writer.WriteAttributeString( name , dc.ColumnName) Writer.WriteAttributeString( rs , number , null, index.ToString()) Writer.WriteEndElement() Writer.WriteStartElement( s , extends , null)...
To add a new node, you simply read until the parent is found and then write an extra set of nodes to the XML writer. Because there might be other nodes with the same name as the parent, use a Boolean guard to ensure that the insertion takes place only once. The following code demonstrates how to proceed if ( Users rw.Reader.LocalName && mustAddNode) rw.Writer.WriteStartElement( User ) rw.Writer.WriteAttributeString( name , name) rw.Writer.WriteAttributeString( role , role) rw.Writer.WriteEndElement() rw.Writer.WriteAttributes(rw.Reader, false) if (rw.Reader.IsEmptyElement) rw.Writer.WriteEndElement() Close the root tag rw.Writer.WriteEndElement() rw.Writer.WriteAttributes(rw.Reader, false) if (rw.Reader.IsEmptyElement) rw.Writer.WriteEndElement() break
Public override void Render(HtmlMobileTextWriter writer) writer.Write( ) writer.WriteBeginTag( input ) writer.WriteAttribute( name , Control.UniquelD) writer.WriteAttribute( type , text ) writer.WriteAttribute( value , ) writer.WriteAttribute( size , 12 ) writer.Write( ) writer.Write( ) writer.WriteBeginTag( input ) writer.WriteAttribute( name , Control.UniquelD) writer.WriteAttribute( type , text ) writer.WriteAttribute( value , ) writer.WriteAttribute( size , 12 ) writer.Write( ) writer.WriteLine( ) writer.RenderEndTag() writer.WriteLine(tableSuffix)
The following code shows how to use these methods to create a copy of the original XML file, modified to skip some nodes. The XML tree is visited in the usual node-first approach using an XML reader. Each node is then processed and written out to the associated XML writer according to the index. This code scans a document and writes out every other node. XmlTextReader reader new XmlTextReader(inputFile) XmlTextWriter writer new XmlTextWriter(outputFile) Configure reader and writer writer.Formatting Formatting.Indented reader.MoveToContent() writer.WriteNode(reader, false) Close the root writer.WriteEndElement() Close reader and writer writer.Close() You can aggregate the reader and the writer in a single new class and build a brand-new programming interface to allow for easy read write streaming access to attributes or nodes.
XmlTextWriter writer new XmlTextWriter(file) writer.Formatting Formatting.Indented writer.WriteStartElement( Wrapper ) ds.WriteXmlSchema(writer) ds.WriteXml(writer) writer.WriteEndElement() writer.Close() If you don't use an XML writer, the WriteXmlSchema method would write the XML declaration in the middle of the document, thus making the document wholly unparsable. You can also mark this workaround with your own credentials using a custom namespace, as shown here writer.WriteStartElement( de , Wrapper , dinoe-xml-07356-1801-1 )
rw.Writer.WriteAttributeString( xmlns , prefix, null, ns) rw.Writer.WriteStartElement(prefix, rw.Reader.LocalName, null) rw.Writer.WriteAttributes(rw.Reader, false) if (rw.Reader.IsEmptyElement) rw.Writer.WriteEndElement() break Close the root tag rw.Writer.WriteEndElement() rw.Writer.WriteStartElement(prefix, rw.Reader.LocalName, null) Because attributes are unchanged, they are simply copied using the writer's WriteAttributes method, as shown here rw.Writer.WriteAttributes(rw.Reader, false)
XmlTextWriter writer new XmlTextWriter( writer.Formatting Formatting.Indented writer.Indentation 2 Next, you simply write the XML document. The only real difference (at least with a simple XML document) between real XML and the code is that the WriteStartElement and WriteEndElement method calls replace the angle brackets. Once you have finished adding the XML document, you finish off with a WriteEndDocument() method. The following code snippet shows how easy writing XML really is start XML document writer.WriteStartDocumentO writer.WriteStartElement( , writer.WriteStartElement( , writer.WriteStartElement( , writer.WriteStartElement( , writer.WriteString( John ) writer.WriteEndElement() writer.WriteStartElement( , writer.WriteString( Doe ) writer.WriteEndElement() writer.WriteEndElement() writer.WriteStartElement( , writer.WriteStartElement( , writer.WriteString( This is the Headline ) writer.WriteEndElement() writer.WriteStartElement( , writer.WriteString( The story is entered here. )...
Using writer As StreamWriter File.CreateText( reminders.txt ) writer.WriteLine( Don't forget Mother's Day this year ) writer.WriteLine( Don't forget Father's Day this year ) writer.WriteLine( Don't forget these numbers ) For i As Integer 0 To 10 writer.Write(String.Format( 0 , , i)) Next writer.Write(writer.NewLine) End Using
Up to now, we've looked at several code snippets showing the XML text writer in action, but without going into details. Let's make up for this now. The necessary steps to create an XML document can be summarized as follows else you might need that the writer supports. The writer maintains an internal node stack and uses it to detect and block erroneous calls such as attributes being created outside the start tag. The writer is smart enough to complete the markup for nodes automatically. This means, for example, that the writer automatically inserts all missing end tags when the writer is closed and completes the markup for the start tag when writing of text or child nodes begins. Close the document At this stage, you close the writer to flush both the contents of the writer and the underlying stream object. At this time only (or prior, if you call the Flush method), the XML text accumulated in an internal buffer is written out and undergoes a summary check for XML well-formedness.
StreamWriter sw new StreamWriter(fileName) XmlTextWriter writer new XmlTextWriter(sw) writer.Formatting Formatting.Indented ds.WriteXml(writer, XmlWriteMode.DiffGram) writer.Close() dsChanges.WriteXml(writer, XmlWriteMode.DiffGram) DataSet dsChanges ds.GetChanges(DataRowState.Added) dsChanges.WriteXml(writer, XmlWriteMode.DiffGram)
define three StringDelegate objects MyClassWithDelegate.StringDelegate Writer, Logger, Transmitter Instantiate the first three delegates, passing in methods to encapsulate Writer new MyClassWithDelegate.StringDelegate( MyImplementingClass.WriteString) Invoke the Writer delegate method Writer( String passed to Writer n ) myMulticastDelegate Writer + Logger ) combine the two delegates, the result is assigned to myMulticast Delegate myMulticastDelegate Writer + Logger Writing string String passed to Writer Logging string String passed to Logger Transmitting string String passed to Transmitter myMulticastDelegate Writer + Logger In the test portion of Example 12-3, the delegate instances are defined and the first three (Writer, Logger, and Transmitter) are invoked. The fourth delegate, myMulticastDelegate, is then assigned the combination of the first two and it is invoked, causing both delegated methods to be called. The third delegate is added, and when myMulticastDelegate is invoked...
The following code shows how to transform the DataSet object into an XPath document and load it into the processor. The result of the transformation is directly written out to an auto-indent XML writer. The argument passed to the style sheet is the name of the first table in the specified DataSet object. Prepare the output writer XmlTextWriter writer new XmlTextWriter(outputFile, null) writer.Formatting Formatting.Indented Call the transfomer and close the writer upon completion xslt.Transform(doc, args, writer) writer.Close()
Public void WriteXml(XmlWriter writer) writer.WriteStartElement( Employee ) writer.WriteStartAttribute( ID ) writer.WriteEndAttribute() writer.WriteString(this.firstName) writer.WriteEndAttribute() writer.WriteStartAttribute( LastName ) writer.WriteString(this.lastName) writer.WriteEndAttribute() writer.WriteEndElement()
Writer.WriteStartDocument() produces writer.WriteStartDocument(true) You close the document writing phase by calling the WriteEndDocument method, as shown in the following code. At this stage, all pending nodes are automatically closed, the internal stack is entirely cleared, and the writer is switched back to its initial state. writer.WriteStartDocument() writer.WriteEndDocument() required to produce an XML file. If you omit such calls, the writer will still work just fine. However, instead of a well-formed XML 1.0 document, you can get a well-formed XML fragment with no root rules applied. writer.WriteComment( Do something here ) text)
In terms of the internal implementation, it is worth noting that the XML DOM's Save method makes use of an XML text writer to create the document. So unless the content to be generated is complex and subject to a lot of conditions, using an XML text writer to create XML documents is faster. The XmlDocument class provides a bunch of methods to create new nodes. These methods are named consistently with the writing methods of the XmlTextWriter class we encountered in Chapter 4. You'll find a CreateXXX method for each WriteXXX method provided by the writer. Actually, each CreateXXX method simply creates a new node in memory, and the corresponding WriteXXX method on the writer simply writes the node to the output stream.
Overloads Public Sub WriteXml (ByVal filename as String stream as Stream writer as XmlWriter writer as TextWriter, ByVal mode as XmlWri teMode ) Overloads Public Sub WriteXml (ByVal filename As String stream As Stream writer as TextWriter writer as XmlWriter, ByVal mode As XmlWriteMode )
Writer.WriteText(item.Text, true) RenderPostBackEvent(writer, (pageStart + i).ToString(), null, true, item.Text, true) writer.WriteBeginTag( a ) RenderPostBackEventAsAttribute( writer, href , (pageStart + i).ToString()) writer.Write( ) writer.WriteEncodedText(item.Text) RenderEndLink(writer)
Exporting the contents of ADO.NET DataSet objects to legacy ADO applications is a problem that we encountered and solved in Chapter 4. That solution was based on a special breed of XML writer. In this section, we'll reconsider that approach and use an XSLT style sheet to accomplish the same task. Bear in mind that using a style sheet to convert a DataSet object to a Recordset object does not necessarily lead to faster code. If we merely consider the transformation process, I do recommend that you always use the writer. Your code is not taxed by the XSLT processor and, perhaps more importantly, you can use a more familiar programming style. The writer is written in C or Visual Basic and, as such, provides you with total control over the generated output. An XSLT style sheet is something different, even though it is often referred to as a program.
Each instance of the XmlSerializer class maintains a reference to the assembly to be used for reading and writing operations. In the preceding pseudocode, tempAssembly is the name of this data member. Both the Serialize method and the Deserialize method use this reference to obtain the tailor-made reader and writer objects to work on the particular type.
In Chapter 20, you learned about the functionality provided by the System.IO namespace. As shown, this namespace provides numerous reader writer types that can be used to persist data to a given location (in a given format). This chapter examines the related topic of object serialization. Using object serialization, you are able to persist and retrieve the state of an object to (or from) any System.IO.Stream-derived type.
The tag enables you to configure aspects of ASP.NET's web services and how they function.Web services are explained in detail in Chapter 10. By using various subtags, you can add protocol types, writer and reader types, as well as configure many other options. All of the subtags supported by the tag support the three attributes of add, remove, and clear.There are two different styles of subtags supported, standard subtags, and type subtags.When using a standard subtag, the add and remove attributes use the name value.When using a type subtag, these attributes use the type value.
The WriteQualifiedName method, however, simply returns the name of the node and can't be used to create the node itself. From this point of view, it is only complementary to methods like WriteStartElement and WriteStartAttribute. You need this method only when you have to write out the name of a node. When the writer is configured to support namespaces (which is the default), the WriteQualifiedName method also ensures that the output name conforms to the W3C Namespaces recommendation as defined in the XML 1.0 specification. You can turn namespace support on and off in a writer by setting the Namespaces property with a Boolean value as appropriate.
XslTransform.Transform(output file or writer, parameter list, encoding format) This method applies the style sheet and saves the result to a file, stream, or writer object. 4. Use the Transform method of the XslTransform object to apply the style sheet and save the results to a file, stream, or writer object. In this step, the XmlDataDocument is used as the input for the transform. Dim writer As XmlTextWriter New XmlTextWriter( xslt_output.html , _ xslTran.Transform(xmlDoc, Nothing, writer) writer.Close() End Sub
The same internal component, the XML tree writer, is used to generate both the ADO.NET XML normal form and the data instance block in a DiffGram. A pleasant side effect of this architecture is that all the mapping features for DataColumn objects we examined in Chapter 9 (see the discussion of the MappingType enumeration in the section Customizing the XML Representation, on page 411) are still valid in the context of a DiffGram. You can decide whether a given column is better rendered using an attribute or an element, or whether the column should be hidden altogether.
This said, there is no absolute guarantee that users won't write badly formed code. If the bad format can be detected, the writer throws an exception. Otherwise, the file is considered correctly written, but client applications might complain about it, as in Figure 4-2. In the check made just before dumping data out, the writer neither verifies the names and semantics of the attributes nor validates the schema of the resultant document, thus authorizing this code to generate bad XML.
The first thing to do is to create a text writer by passing the filename to the constructor. We can't use the filename passed in f ileSelector . PostedFile . Filename, however, as that path will be local to the submitting client. We must extract the unqualified filename from that string, and provide a path to a directory on our server. Now that we've got a suitable filename, we can call the XmlTextWriter constructor. We've chosen UTF-8 encoding, which will be picked up when we write an XML declaration in the next section. While we're at it, we tell the writer that we want indented output using the Formatting property, and set the indentation to three characters
During the process of building a good Web site, you will most likely need the skills of an artist, writer, lawyer, layout designer, coder, and many others. Few people have all these skills. True, for a small Web site you might be able to get by on the skill of one person, but then this site will probably be made up of only a handful of pages and have no real need for a CMS anyway. Heck, a person that manages a site this small probably isn't even going to read this book.
The Load and Transform methods have several overloads each. In all this richness of call opportunities, not all possible combinations of input and output channels are always supported. For example, you can load the source document from a URL, but only if you output to another URL or disk file. Likewise, if you want to transform to a text writer, you can't load the source from a file. Table 7-6 and Table 7-7 provide a quick-access view of the available overloads.
Assuming you have an object from the Invoice class th at you want to serialize, you use the System.Xml.Serialization.XmlSerializer class. You call the Serialize method on this class passing it the Invoice object and one of the following Stream, TextWriter, or XmlWriter. The XmlSerializer uses reflection to read public properties and fields of the I nvoice object and serialize them as XML to the supplied stream or writer. The XmlSerializer automati cally determines the structure of the generated XML document unless you use attributes to influence that structure. Figure 2-4 shows two of the commonly used attributes XmlElementAttribute and XmlAttributeAttribute. These are .NET CLR attributes not XML attributes. .NET attributes are classes that inherit fro m System.Attribute and their names typically end with Attribute (by convention). These classes are used to add metadata to the assemblies, which can be used at runtime to add functionality. For example, by adding the XmlElementAttribute...
By the way, many third-party software can also test if an XML document is well-formed, and if it is valid (against a given schema). In this context, we have found the XML Authority (by TIBCO) and XML Writer (by Wattle Software) to be very good. An excellent tool named XSV is also available from www.w3.org 2000 09 webdata xsv.
In the non-deterministic world of .NET we should always make sure that we call the Close method on our streams. If we don't call Close, the time at which the buffered contents of a stream will be written to the underlying backing store is not predictable (due to the way the CLR garbage collector works). Furthermore, since garbage collection does not guarantee the order in which objects are finalized, we may also find our data is not written correctly and may be corrupted. For example, it is possible for a stream to be closed before a writer object has flushed its data.
Once you have added the .resx file to the project, you should add the bare minimum of resource file contents the node and the three nodes I mentioned earlier ResMimeType, Reader, and Writer. After that it makes sense to add at least one node (essentially as a template), and then you can edit the resource file using the XML designer.
StreamReader's constructor can throw exceptions of type System IO FileNotFoundExceptionA, System IO PathNotFoundExceptionA, and System IOExceptionA. An IOExceptionA can also be thrown from the stream writer Console Out. Figure 3-5 shows the inheritance tree for these exception classes.
The text of this message is typical of errors associated with race conditions. The two writer threads most likely attempted to add an entry to the queue at the same time. The steps leading up to the error probably went something like this. One of the threads attempts to add an entry to the queue (figure 7.3).
StringWriter writer new StringWriter() ser.Serialize(writer, emp) string xmlText writer.ToString() writer.Close() be successfully reflected. The true reason for the exception is slightly more subtle, however. The XmlSerializer class needs to create internally an instance of the target class to collect all the information necessary to create the serialization reader and writer objects. The serializer can't make assumptions about the constructors available on the class, so it always uses the default constructor. If there is no such constructor, an exception is thrown.
Public Class MainForm Private Sub btnGenResX_Click(ByVal sender As System.Object, _ ByVal e As System.EventArgs) Handles btnGenResX.Click ' Make a resx writer and specify the file to write to. Dim w As New ResXResourceWriter( C ResXForm.resx ) ' Add happy dude and string. Dim bMap As New Bitmap( happyDude.bmp ) w.AddResource( happyDude , bMap) 117
Throw New Exception( Writer lock held before acquire ) End If Try Do Loop until the writer lock is acquired Once the update is complete, release the writer lock Throw New Exception( Writer Lock still held after release ) End If End Try End Sub Acquire- AcquireWriterLock is a method on the ReaderWriterLock class WriterLock that allows a thread to request ownership of a write lock. It accepts a timeout parameter and throws an ApplicationException if the lock cannot be acquired in the specified time period. Reader Writer Lock There are times when it's unclear if the lock required will be a reader or a writer. For example, in the auction simulation, in order to determine if a new bid is higher than the existing bid we must first look at what the current bid is (listing 9.4). Once we've examined the current bid, we can see if the new bid is higher. throw new Exception( Writer Lock held before acquire ) See if we need to acquire a writer lock if ( ItemLock.IsWriterLockHeld) a writer lock...
We've seen that the Queue class in the Collections namespace is not thread-safe. This is the general rule for collections, with the exceptions of the Hashtable and ArrayList classes. Hashtable is thread-safe for multiple readers and a single writer. Multiple threads can read from the same Hashtable safely as long as no more than one thread is updating it. This is most likely because a reader-writer lock guards the Hashtable's data. In the next chapter we'll discuss reader-writer locks. The ArrayList class is thread-safe for multiple readers. This means that multiple threads can be reading from the same ArrayList as long as no thread attempts to update it.
Welcome to the second edition of Professional Crystal Reports for Visual Studio .NET. Crystal Reports is one of the world's leading software packages for creating interactive reports that can be integrated into a wide range of Windows and Web applications. With more than four million licenses shipped, Crystal Reports is the leader among Windows report writers. Crystal Reports has been in the Visual Studio box since 1993, but with the introduction of Visual Studio .NET 2002, a new version, Crystal Reports .NET, was integrated more closely than ever before. And with the release of Visual Studio .NET 2003, the bar has been raised even higher, with tighter integration and more reporting options. This book will detail the functionality provided with Crystal Reports for Visual Studio .NET 2003 and how, when, and where you should integrate reports into your .NET applications.
The processing for Step Into, Step Over, and Step Out seems straightforward, but there's one small twist that you need to consider. If you write your debugger to handle Step Into, Step Over, and Step Out, what are you going to do if you've set the one-shot breakpoint for those cases and a regular breakpoint triggers before the one-shot breakpoint As a debugger writer, you have two choices. The first is to leave your one-shot breakpoints alone so that they trigger. The other option is to remove your one-shot breakpoint when the debugger notifies you that a regular breakpoint triggered. The latter option is what the Visual Studio .NET debugger does.
Public override void Render(HtmlMobileTextWriter writer) writer.Write( ) listSuffix r n writer.AddAttribute( width , 90 ) writer.AddAttribute( cellpadding , 3 ) writer.RenderBeginTag( table ) writer.WriteLine( ) writer.Write( ) writer.EnterFormat(Style) writer.ExitFormat(Style) writer.WriteLine( ) writer.Write( ) writer.EnterFormat(Style) writer.ExitFormat(Style) writer.WriteLine( ) writer.RenderEndTag() writer.WriteLine(listSuffix) public override void Render(WmlMobileTextWriter writer) Write beginning of table writer.EnterLayout(Style) writer.EnterFormat(Style) writer.RenderText( ) First datacell writer.Write( ) writer.RenderText(Control.Item1Text, true) writer.RenderText( , false, false) second datacell writer.RenderText(Control.Item2Text, true) writer.RenderText( , false, false) writer.WriteLine( ) close table and output a trailing break writer.ExitFormat(Style) writer.ExitLayout(Style, true)
Public override void Render(HtmlMobileTextWriter writer) writer.Write( ) listSuffix r n writer.AddAttribute( width , 90 ) writer.AddAttribute( cellpadding , 3 ) writer.RenderBeginTag( table ) writer.WriteLine( ) (CMTableListItem)(items pageStart + i ) writer.Write( ) writer.EnterFormat(Style) writer.WriteEncodedText(item.Text) writer.ExitFormat(Style) writer.Write( ) writer.EnterFormat(Style) writer.WriteEncodedText(item.Text2) writer.ExitFormat(Style) writer.WriteLine( ) writer.RenderEndTag() writer.WriteLine(listSuffix)
One of the most common techniques of virus writers is to exploit buffer overruns so that they can redirect the return address to malicious code. Fortunately, the gs switch inserts security checks to ensure that the return address isn't overwritten, which makes writing those kinds of viruses much more difficult. gs is set by default in release builds, and I would encourage you to use it in your debug builds as well. The first time it tracks down that one wild write that just so happens to overwrite only the return address, you'll see how
Over the years, I've been amazed at the number of engineers who are interested in writing debuggers. I'm not amazed at why they want to do it since I've lived the debugger writer's life. We got interested in computers and software in the first place because we wanted to know how they worked, and debuggers are the magic looking glass that lets you see anything and everything about them. Consequently, I've received quite a bit of mail asking me what it takes to write a debugger and for advice on how to proceed. Part of my motivation for writing WDBG was to finally get a full example out for engineers to see how debuggers work.
In this case, when SOAP encoding is involved, the serializer does not generate a well-formed XML document. More precisely, the XML code is correct, but the document has no root, because the child class is written at the same level as the parent class. If you don't explicitly serialize to a writer with a user-defined root, a writing exception is thrown.
If you read the previous chapter, you know that it's easy to set the thread name appearing in the Threads window. Microsoft has documented a way to do the same thing in native applications. By default, native applications show the name of the function where the thread started. To show the actual name, you can use a special exception value to pass in a new name to use, and the debugger writer must read the memory address passed as part of the exception. I wrapped up the necessary code into a set of functions in BUGSLAYERUTIL.DLL BSUSetThreadName and BSUSetCurrentThreadName. The code for BSUSetThreadNameA is shown here. After calling this function, the Threads
Dim writer As XmlTextWriter _ New XmlTextWriter(filename, Encoding.UTF8) writer.Formatting Formatting.Indented writer.WriteStartElement( CompanyInfo ) writer.WriteEndElement() writer.Close() XmlTextWriter writer new XmlTextWriter(filename, Encoding.UTF8) writer.Formatting Formatting.Indented mySerializer.Serialize(writer, myCompany) writer.WriteEndElement() writer.Close()
Robin's interest in computing began when she taught herself to program in C to fulfill a programming language requirement for her master's degree in biomathematics at the University of Washington. Fascinated by the subject, Robin attended as many computer science classes as her schedule would permit, and took a position as a programmer with the University of Washington after graduation. Robin spent several years in the biotechnology industry, writing data applications in various database management systems, C, and Microsoft Visual Basic. Not content to just read computer science and software engineering books, she then pursued and completed a master's degree in software engineering at Seattle University. During these years, Robin presented training sessions on software engineering topics to her peers. After so many years in the classroom, Robin wanted to try teaching, and jumped at the opportunity to teach object-oriented programming with Visual Basic for the University of Washington...
Writer.WriteStartDocument() writer.WriteComment( Contains a BinHex JPEG image ) writer.WriteStartElement( jpeg ) writer.WriteAttributeString( FileName , filename) Write the JPEG data writer.WriteBinHex(img, 0, size) writer.WriteEndElement() writer.WriteEndDocument() FileMode.Create) BinaryWriter writer new BinaryWriter(fs) writer.Write(img) writer.Close()
Writer.WriteElementString( MyNode , Sample text ) writer.WriteStartDocument() Write DOCTYPE and entities writer.WriteDocType( MyDef , null, null, Open the root writer.WriteStartElement( Cities ) Open the child writer.WriteStartElement( City ) writer.WriteAttributeString( Zip , 12345 ) Write the State attribute (reference an entity) writer.WriteStartAttribute( State , ) writer.WriteEntityRef( I ) writer.WriteEndAttribute() Write the body of the node (reference an entity) writer.WriteEntityRef( I-Capital ) Close the current innermost element (City) writer.WriteEndElement() Close the current innermost element (Cities) writer.WriteEndDocument() Close the document writer.WriteEndDocument() writer.WriteStartAttribute( Country , ) writer.WriteEntityRef( I ) writer.WriteString( , Europe ) writer.WriteEndAttribute() As you might have noticed, the end tags for both attributes and nodes do not take any arguments. The writer maintains an internal stack of opened attributes and nodes and...
The classes StreamReader and StreamWriter provide an implementation of the TextReader and TextWriter that works with any class derived from Stream. You associate a StreamReader or StreamWriter with a stream by passing the stream in the StreamReader or StreamWriter constructor. You can also directly instantiate a StreamReader or StreamWriter directly from a file's path name. The classes String-Reader and StringWriter provide an implementation of the TextReader and Text-Writer on variables of class System.String. Several other namespaces contain other classes that derive from TextReader and TextWriter, implementing their philosophy on other types of media.
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