How to Make Money with Bitcoin
In this lab, you will create a simple Currency Converter Web application that uses the user' s culture to determine the type of conversion to perform Figure 15-11 Currency converter (fallback interface) Figure 15-11 Currency converter (fallback interface) Exercise 1 Creating the Currency Converter Web Form The Currency Converter Web application contains a single Web form that receives input from a text box and displays output in two labels when the user clicks OK. The Web form also includes a Cancel HTML button that clears the text box. To create the Currency Converter Web form 1. Create a new Web application project named CurrencyConverter.
The Currency type in Visual Basic .NET is also no longer available. It should be replaced in most circumstances with the Decimal data type (which is 96 bits, enough for financial calculations). The new 64-bit Long may also be useful in some logic doing currency manipulations because it is not subject to the size limitations of the old 32-bit Long. As in VB6, the Format function can be used to format a currency value for output.
The application works on a database that contains two tables ExchangeRates and Countries. The Countries table contains the name of the country (e.g., United States, United Kingdom, etc.), the currency type name (dollars, pounds, etc.), and an image of the country's flag. The ExchangeRates table contains exchange rates between two countries with the rate information and the date the rate was based on. The country information is stored in the ExchangeRates table as foreign keys in the Countries table. Figure 4.7 shows the schema for this data in the data set designer diagram. You can see that there are two foreign key relations from ExchangeRates to Countries, one for the CountryFromID column and one for the CountryTolD column.
The ICurrencyManagerProvider interface lets a container indicate whether it provides its own currency manager for any contained data collections. This interface is implemented by the BindingSource component, and you shouldn't have to implement it yourself. However, you may occasionally need to use this interface to access the Currency Manager for a container from a custom bound control. The ICurrencyManagerProvider interface has two members a method namedGetrelatedCurrencyManagerand a property named CurrencyManager. The CurrencyManager property is the main thing you'll use to get a reference to the underlying currency manager to subscribe to change notifications on that currency manager. (An example using this is shown in Chapter 8 on the FilteredGrid control.) The GeTRelatedCurrencyManager method lets you specify a data member parameter, which lets you get a child collection's currency manager in a master-details data-binding scenario.
Format Currencyexpression[ numDigits AfterDecimal [ includeLeading Digit[ useParens ForNegative Numbers[ groupDigits
This function returns a numeric expression formatted as a currency value (dollar amount) using the currency symbol defined in Control Panel. All arguments are optional, except for the expression argument, which is the number to be formatted as currency. numDigitsAfterDecimal is a value indicating how many digits will appear to the right of the decimal point. The default value is 1, which indicates that the computer's regional settings must be used. includeLeadingDigit is a tristate constant that indicates whether a leading zero is displayed for fractional values. The useParensForNegativeNumbers argument is also a tristate constant that indicates whether to place negative values within parentheses. The last argument, groupDigits, is another tristate constant that indicates whether numbers are grouped using the group delimiter specified in the computer's regional settings.
The .NET Framework offers solutions to all these problems. First it provides a system of data types that can be marshaled between multiple .NET languages without any loss of fidelity. Developers using the .NET Framework will no longer have to worry about what language might be consuming the class or component they're writing. They can spend more time solving the problem at hand and less time worrying about how the C++ client for the server program is going to interpret a string or a currency type.
To demonstrate some of the things you can do through binding events, the download code for this chapter contains a project named BindingEvents, which contains the currency exchange rate application shown in Figure 4.6. To use this application, you first have to create a new database called MoneyDB. There is a script named MoneyDB.sql in the download code for Chapter 4 that you can run from SQL Query Analyzer to create and populate the database with some sample data. There is also an additional application called MoneyDBAdmin that you can use to edit, add, or delete data from the tables in this database.
From currency type text box Binding currencyFromBinding new Binding( Text , m_ExchangeRatesBindingSource, CountryFromID ) currencyFromBinding.Format + new To currency type text box Binding currency ToBinding new Binding( Text , m_ExchangeRatesBindingSource, CountryTolD ) currency ToBinding.Format + new m_Currency Type To TextBox. DataBindings.Add(currency ToBinding) You can see from theCreateBindings method that this subscribes to theFormat and Parse events on the binding object for each of the country name text boxes, and only the Format event for the currency type text boxes since they are read-only. Also note that both the country name and currency type text boxes for From and To information use CountryFromID and Country TolD from the ExchangeRates table, respectively. Because the country name, currency type, and flag are determined by the foreign key stored in the ExchangeRates table, the data-binding process effectively denormalizes the data back into a flat set of data for...
Let's look now at how to add a Unit Price column. Ideally, we would show the price as currency and we can do this by applying a format string to the column. Try It Out - Adding a Currency Column view as before and add a new Bound Column. Set the Header text to Unit Price and the Data Field to unitprice. Insert 0 c in the Data formatting expression box. This isn't just an extravagant two-way smiley it also tells ASP.NET that this column is a currency, as explained later.
Allowing the user to choose a culture is better than accepting the existing culture of the application. There's no need to prompt or store a currency symbol when all necessary currency symbols are stored in the .NET Framework. For more information, see the section Setting Culture Properties in this chapter.
How Do I Display Multiple Currencies (the Euro and local currency) The System.Globalization.NumberFormatInfo class contains formatting information such as the currency symbol, decimal digit, separator, and so on. In many European countries, two separate currencies are commonly used the Euro and the local currency. A static property NumberFormatInfo.CurrentInfo contains current local currency info, and the Currency symbol that is associated with the Euro. To represent the local currency and the Euro, you must first create a copy of the NumberFormatlnfo instance using NumberFormatInfo.Clone(), then replace the CurrencySymbol property with the local currency symbol. Dim LocalFormat As NumberFormatlnfo NumberFormatlnfo) LocalFormat.CurrencySymbol DM ' Replace currency symbol with DM symbol.
The .NET Compact Framework platform intrinsically handles all date, time, numbers, and string formatting whenever the mobile user changes the current culture of the device. However, there might be cases when your code needs to know the current culture of the device. For example, currency conversion is something the platform does not do for you automatically. You might wish to find out what the default currency of the mobile device is set to and use that to automatically calculate and display its equivalent value in US dollars. The following code snippet allows you to retrieve the current culture of the mobile device. Using the Cultureinfo object, you can query a rich set of information about the language, date time format, numerical format, and currency of the mobile device. _summary + Lang + _culture.ThreeLetterISOLanguageName + r n _summary + Currency + _culture.NumberFormat.CurrencySymbol + r n _summary + Decimal Separator + Culture Japanese (Japan) Date yyyy' 'M' 'd'B' Lang jpn...
If you read and understood the discussion of currency managers in the last chapter, you probably already understand the problem. If both sets of controls are bound to the same data source, there is one currency manager created for that data source, and there is only one current item evenn that currency manager. Updating the current item in one of the sets of controls immediately updates the controls in the other set because they are bound to the same data source, and the currency manager for that data source keeps all controls bound to the data source synchronized to the current item. So to fix that problem you need to maintain two separate currency managers for the two sets of controls. You could get two separate copies of the data, and each would have its own currency manager as separate data sources. However, a better approach is to have two separate country binding sources, each bound to the same underlying single Countries table in the data set. This does exactly what's needed...
The problem with the data navigator is that it is hooked directly to the customersBindingSource in the form, and there is no automatic way for it to cascade the changes in the position for that binding source down into the one in the user control (m_BindingSource). This is because each binding source has its own currency manager under the covers, and they aren't hooked up in a way that lets the binding sources know they are supposed to stay synchronized. To fix this, you need to do a little more work when you hook up the data source in the user control. Chapter 7 briefly covered thelCurrencyManagerProvider interface, which is implemented by objects that host their own currency manager, as is the case with a BindingSource component. To be notified when the currency manager's position in the form's binding source changes within the user control's binding source, you need to use the ICurrencyManagerProvider interface to detect when something will maintain its own currency manager, and...
Currency Format Label2.Text Format(500, Currency ) Label4.Text Now.ToShortDateString 12. Press F5 to build and run your application. Click each button to see a localized form. Note that the appropriate format for currency and the date is displayed in the localized form and that the new strings are loaded for the German form.
RegionInfo contains information for a given region including DisplayName, currency information, and official abbreviations. RegionInfo also contains a static property to retreive the CurrentRegion. Dim R As RegionInfo New RegionInfo( us ) Console.WriteLine ( The name of this region Console.WriteLine ( The currency symbol for Console.WriteLine ( Is this region metric the region is 0 , R.CurrencySymbol) 0 , R.IsMetric)
Localization is the process of translating local specific application elements to a particular locale. These elements include textual elements, visual elements, and content. This also affects how money is handled unless the currency is universal, like the Euro for Europe. For applications it affects, localization resources need to be created during the development process. An example from our case study would be that it must be able to be viewed in English and Spanish. This locale setting is determined by the user's browser.
The form itself has a BindingContext property that holds a collection of synchronization objects for each data source that is being used for data binding on the form. For the most part in .NET 2.0, you don't have to deal directly with the binding context in your code, but it is still lurking under the covers making things work. (In .NET 1 .X, you had to go through the binding context to get to the synchronization objects for a number of scenarios.) As discussed in the previous section, what gets created behind the scenes are instances of a CurrencyManager for list-based data sources or aPropertyManager for individual custom business objects. Each of these classes derives from BindingManagerBase, which is the type of object reference that theBindingContext is designed to contain. The CurrencyManager is the one you will deal with most often. A container component (such as a Form or a BindingSource) creates a currency manager for each list-based data source that you specify for a control...
The System.Globalization namespace contains classes that enable your applications to determine the locale at run time. This gives you the flexibility of creating applications that can automatically adapt themselves to the locale in which they run. The classes of the System.Globalization namespace define culture-related information, such as the language, the country region, the calendars in use, the format patterns for dates, currency, and numbers, and the sort order for strings. The following sections describe the CultureInfo and RegionInfo classes of this namespace.
So far you've seen how to use the CurrentCulture property to handle localized formatting of things such as currency, dates, and numbers. But localizing the text displayed on the user interface is perhaps even more important. The .NET Framework offers support for user interface localization through its capability to select a set of user interface resources at runtime.
Currency Currency The currency format string converts the numerical value to a string containing a locale-specific currency amount. By default, the format information is determined by the current locale, but this may be changed by passing a NumberFormatlnfo object. The NumberFormatInfo class is used to control the formatting of numbers. By setting the properties in this class, the programmer can control the currency symbol, decimal separator, and other formatting properties.
Labe11.Text 500.00 Labe12.Text Format(500, Currency ) When the culture is set to en-US, which represents the English language, United States as the region (which is the default culture setting for computers in the United States), both labels will display the same string that is, 500.00 . When the current culture is set to fr-FR, which represents French language, France as the region, the text in the two labels will differ. The text in Label1 will always read 500.00 because it is not formatted by the application. The text in Label2, however, will read 500,00 . Note that the currency symbol is changed to the appropriate symbol for the locale in this case the Euros symbol and the decimal separator is changed to the separator that is appropriate for the locale (in this case, the comma).
Your application automatically reads the culture settings of the system and implements them. Thus, in most circumstances, you will not have to manually change the culture settings. You can, however, change the current culture of your application in code by setting the current culture to a new instance of the CultureInfo class. The CultureInfo class contains information about a particular culture and how it interacts with the application and system. For example, the CultureInfo class contains information about the type of calendar, date formatting, currency formatting, and so on for a specific culture. You set the current culture of an application programmatically by setting the CurrentThread.CurrentCulture property to a new instance of the CultureInfo class. The CultureInfo constructor requires a string that represents the appropriate culture code as a parameter. The following code example demonstrates how to set the current culture to French Canadian
The OrderItemControl control is under development and requires code to bind constituent controls to data from the Products table. A method in the control called GetProductData has been created, and it accepts a parameter named productsTable that contains data from the Products table. You need to bind data from this table to the constituent controls. You also need to convert the values in the Price column to currency when you bind them to UnitPriceTextBox control. ConvertEventArgs event argument to a currency format.
In our demonstrations, we will use a sample database named Products.mdb, which you can find on the CD accompanying this book. It is a Microsoft Access 2000 database. It contains only one table, named Products. Figure 3.66 shows some sample records in this table. Basically, the table has four columns ProductId (AutoNumbered Long Integer), ProductName (Text 50), ImagePath (Text 150) and Price (Currency).The ImagePath column contains the name and location of an image relative to a virtual directory.
Protected gStrings As New _ GetType(WebForm1).Assembly) typeof(WebForm1).Assembly ' Get the user's preferred language. Dim sLang As String Request.UserLanguages(0) ' Set the thread's UICulture to load resources. Thread.CurrentThread.CurrentUICulture New CultureInfo(sLang) ' Set the thread's culture for date string currency formats. Thread.CurrentThread.CurrentCulture _ Thread.CurrentThread.CurrentUICulture new CultureInfo(sLang) Set the thread's culture for date string currency formats. Thread.CurrentThread.CurrentCulture
The BindingSource component uses this internally to provide better currency of the presented data in bound controls, even if the underlying objects don't support property change notifications themselves. To implement support for raising the ListChanged event in response to property value changes on the collection objects, you have to provide a callback delegate to the property descriptor for each property on each object in a collection, so that your collection will be notified when those properties change through the property descriptor. You do this through the AddValueChanged method on the PropertyDescriptor class. See theBindingListView class implementation in Chapter 9 for an example and more discussion of this.
Before you can start localizing applications, you need to understand the concept of a culture. A culture, in .NET terms, is a more precise identifier than a location or a language. A culture identifies all the things that might need to be localized in an application, which requires you to know more than just the language. For example, just knowing that an application uses English as its user interface language doesn't give you enough information to completely localize it Should you format dates and currency amounts in that application in a way appropriate to the United States, the United Kingdom, Canada, Australia, or New Zealand (among other possibilities) Similarly, just knowing the location isn't enough If an application will be used in Switzerland, there are four possibilities for the user interface language. Each combination of location and language identifies a culture.
In the EditltemTemplate we set up a textbox to handle the display of editable data and gave it an id of editprice. Additionally we set up a validation control with an id of valed-itprice to make sure that the user enters a positive currency value. Below we will cover how we use the validation control to validate the users input. Dim paramO as New OleDBParameter( price , OleDBType.Currency)
Developers often need to validate a control based on a range of values. For these cases, you can use the RangeValidator Web server control. You can have different types of ranges, including ranges based on currency, dates, doubletype data, integer-type data, and string data. If the user does not type input that falls within a valid range, a validation message appears, and the user gets a chance to correct the form and resubmit it.
The parameterless ToString method has two problems. First, the caller has no control over the formatting of the string. For example, an application might want to format a number into a currency string or a decimal string, or a percent string or a hexadecimal string. Second, the caller can't choose to format a string using a specific culture. This second problem is more troublesome for server-side application code than for client-side code. On rare occasions, an application needs to format a string using a culture different from the culture associated with the calling thread. To have more control over string formatting, you need a version of the ToString method that allows you to specify specific formatting and culture information. Also, all the built-in numeric types support C for currency, D for decimal, E for scientific (exponential), F for fixed-point, G for general, N for number, P for percent, R for Culture-sensitive information applies when you're formatting numbers (including...
The data type of the values being compared. The values are converted to this type before the comparison is made. The possible values are Currency , Date , Double , Integer , and String . The data type of the value being validated. The value being validated, as well as the maximum and minimum values, are all converted to this type before the comparisons are made. The possible values are Currency , Date , Double , Integer , and String . The default is String .
From the case study, examples of localization, internationalization, and globalization would be the ability for the web site to support English, Spanish, German, and French. Each language would require specific types of routines to display appropriate types of currency and date information. Another requirement would be the fact that the application would have to use .NET's features of localization resource files to hold language-specific information.
The Formi form uses standard mobile controls to accept input from the user. Then the inserts WML code for a , which renders as a softkey or another link with the legend Convert . When selected, this calls the convert function in the WMLScript file called currency.wmls, which it fetches from the content server. The convert function takes arguments that are the values the user entered (the variables SelectionListi, SelectionList2, and TextBoxi). Figure 8-19 shows the resulting WML markup.
Write code to detect the user' s culture and set the Thread class' s CurrentCulture and CurrentUICulture properties to match. The CurrentCulture property determines how ASP.NET formats dates, currency, and numbers the CurrentUICulture property determines which satellite assembly is used when loading translated strings.
As mentioned, the application also lets users type a country name into the From Country or To Country text boxes, and it will update the country information based on that input. The things that need to be updated are the currency type and flag for the entered country name, and the corresponding country ID that is set in the current ExchangeRates row. You could deal with this kind of situation by handling the TextChanged event on the text box and doing the lookup of the entered country name in that handler, but I wanted to show how you can accomplish this using data-binding mechanisms. The sample has the Parse event on the country name text box intercept the changed country name. The Parse event will be fired when the contents of theTextBox have changed and the focus changes to another control (after Validating and Validated events fire).
The balance is stored in a decimal field. The decimal data type (System.Decimal) is used to store numbers with a particular precision. Thus 2.37 is stored as 2.37, not something extremely close to 2.37, as might happen in using a System.Double variable. The advantage of using the System.Decimal data type is that rounding doesn't occur, so the System.Decimal type is appropriate for representing currency.
If you look back at the earlier screenshot, you can also see the results of setting the DataTextFormatString property of the ASP DropDownList and ASP ListBox controls. For example, in the last four lines of the preceding code we bound the second ASP ListBox control to the HashTable so that the text of each element is automatically formatted as a currency value.
This is because a primary or foreign key can encompass more than one column - for example the only possible primary key for the BookPrices table in our database is the combination of the ISBN code and the currency name. None of the individual columns has values that are unique the table, and only a combination of columns can provide a unique key value. However, the ISBN column alone provides the link to the parent BookList table, and so we specify it as a foreign key in
You can format the items that you display in a list-based control. For example, if you are displaying a list of monetary values, you can format them all as currency, and they will be displayed in the currency format that is appropriate to the culture the application is running under.
Consider the following example, where an integer will be displayed as a currency string. With the standard ASP.NET data binding syntax, you must first cast the type of the data row in order to retrieve the data field, IntegerValue. Next, this is passed as an argument to the String.Format method.
In this example, the DataType is a string for all DataColumn objects except salary, which is a decimal object that contains currency. The MaxLength property constrains the length of string data. The string data is truncated if you exceed this length and no exception is thrown. If the Unique property is set to true, an index is created to prevent duplication of entries. The AllowDBNull property is set to false to mandate the population of the column with data. The Caption property is a string that holds the column heading that is to be displayed when this DataTable object is used with Web server controls. The lastNameFirstName DataColumn object shows how an expression column is created, in this case, by assigning an expression. Expression columns are also known as calculated or derived columns. Adding a derived column is especially beneficial when data is available but not in the correct format.
Another problem is that you can actually overwork the data structures. One such example is the LARGE_INTEGER data type. The reason that the C C++ headers create such a complex structure for this data type is that many C C++ compilers don't support 64-bit integers natively. This concept is something you should keep in mind as you create data structures. For example, you might find the need to use a Currency data type in one of the structures. This is a data type that some C C++ compilers don't support natively, yet the support is easily accessible from the .NET Framework. In sum, don't always re-create everything you find in the header files because you won't always need to do so.
The MinimumValue and MaximumValue properties contain the limit of values the user can input. You'll use the Type property to determine what type of data the control will accept. The RangeValidator accepts common types including string, integer, double, date, and currency. If the input doesn't fall within the selected range of values or is of the wrong type, the control will display an error message.
The string can contain a valid decimal-separator character. NumberFormatinfo's NumberDecimalseparator and CurrencyDecimalseparator propertie s determine valid decimal-separator The string can contain a valid grouping-separator character. NumberFormatInfo's NumberGroupSeparator and CurrencyGroupSeparator properties determine valid grouping-separator characters. NumberFormatInfo's NumberGroupSizes and CurrencyGroupSizes properties determine the number of digits in the group. The string can contain a valid currency symbol, which NumberFormatInfo's CurrencySymbol property determines. Currency
Use the Web.config file' s globalization element to create a culture-specific Web application. The culture attribute of the globalization element determines how the Web application deals with various culture-dependent issues, such as dates, currency, and number formatting. At run time, the Web application displays dates, currency, and number formats according to the culture attribute setting in the Web.config' s globalization element, as shown in Figure 15-2.
Just as the Currency Converter displays a different interface for different cultures, it also performs different conversions based on the current culture. In this exercise, you will write the code that performs the culture-dependent conversions. ' Culture variables for currency formatting. Dim Europe As New CultureInfo( fr-FR ) Dim USA As New CultureInfo( en-US ) Dim Mexico As New CultureInfo( es-MX ) Culture variables for currency formatting. CultureInfo Europe new CultureInfo( fr-FR ) CultureInfo USA new CultureInfo( en-US ) CultureInfo Mexico new CultureInfo( es-MX ) The preceding code creates Culturelnfo objects (Europe, United States, and Mexico) for each cultural conversion. These objects provide the appropriate currency formatting in the ToString methods. The Europe object uses the culture code for France, because France uses the euro as currency. There isn' t a culture code for the European Union.
The trigger for formatting is usually when the current item in a data source is being set, or when the property in the current item for a given binding object is changed. The current item in the data source is set when the data first loads, and again at any time the Position property on the CurrencyManager for the data source changes. For a tabular data source, such as a data set, the current item is the current row of the data table. For an object collection, the current item is an object reference to one of the objects in the list. If you use the binding source to separate your bound controls from your data sources as recommended, then you don't have to worry about the CurrencyManager just think of it in terms of thePosition and Current properties on the binding source. TheBindingSource component encapsulates a currency manager and exposes its properties and events in an easy-to-use API, so you almost never need to worry about the currency manager.
DataMember public string Currency StockPrice s new StockPrice() s.Ticker id s.DailyVolume 45000000 s.CurrentPrice 94.15 s.CurrentTime System.DateTime.Now s.Currency USD return s MetalPrice g new MetalPrice() g.Metal id g.Quality 0.999 g.CurrentPrice 785.00 g.CurrentTime System.DateTime.Now g.Currency USD return g DataMember public string Currency
One limitation in your current example is that there is no way to handle data that need to be formatted before they can be displayed. For example, the UnitCost is displayed in the form 1.9900 instead of the more appropriate currency string 1.99. There are several extra parameters at work here. The first new parameter (true) enables formatting. The next parameter specifies the default update mode, which applies changes to the bound object after validation is performed. This doesn't represent a change, but a value is required for this version of the Add() method. The following parameter (0) sets the value that's used if the bound field is null, and the final string sets the format (C for currency), which ensures the UnitCost field is displayed with a currency symbol and two decimal places (see Figure 8-11). Currency Brackets indicate negative values ( 1,234.50). The currency sign is locale-specific.
To navigate programmatically, you need to access the form's BindingContext object, find the correct CurrencyManager, and modify its Position property. Unfortunately, to find the correct CurrencyManager object, you need to submit the data object you used for your binding. That means you need to keep track of the data object in a form-level variable, or look up the CurrencyManager immediately after you perform the binding and track it in a form-level variable. The following example demonstrates the second technique. First, create the variable for storing the CurrencyManager object This is a CurrencyManager, but we don't need to perform a cast because the BindingManagerBase exposes all the properties we need to use. private BindingManagerBase storeBinding Keep track of the currency manager. storeBinding this.BindingContext dt
You can increase the usability of your application in certain parts of the world by offering an interface that's translated into the user's preferred language as well as formatting currency and dates according to cultural norms. ASP.NET has a number of features to help you build applications that provide content appropriate for a specific culture. Local conventions for formatting currency, weights, and measures. The System.Globalization.NumberFormatInfo class can help with this. Globalization is the process of building in support for culture-specific date formats, character sets, currency formats, and units of measure. The management of string resources for different languages is called localization.
If you ran the CustomBusinessObjects sample from the last section, and edited a property on either a Customer or Order object in the grid, then tabbed into the next field, the edit to that property is immediately written to the underlying bound object property. If there are any other controls that are data bound to the same object and displaying it, you should see their display immediately update to the new value as well. This is because the change was made through a data-bound control, which notifies the currency manager controlling the data binding of the change, and that change will then be rippled to any other bound controls that are in communication with the same currency manager.
Add a member to track parent currency manager private CurrencyManager m_CurrencyManager null If there is an existing parent currency manager, unsubscribe from its event and get rid of the ref if (m_CurrencyManager null) m_BindingSource.DataSource value Check to see if the new data source provides its own currency manager ICurrencyManagerProvider currmgr value as ICurrencyManagerProvider If so, subscribe to be notified when the parent current item changes m_CurrencyManager currmgr.CurrencyManager m_CurrencyManager.CurrentltemChanged + OnCurrencyManagerPositionChanged As shown in Listing 8.3, each time a new data source is assigned, you have to check to see if it implements thdCurrencyManagerProvider interface. If so, you subscribe to the CurrentltemChanged event on theCurrencyManager exposed through the interface property. You also need to hold on to a reference to the currency manager, so you can unsubscribe from that event before releasing the reference to the data source when a new...
In Chapter 5, you used the following formatting expression to display a System.Decimal value as a currency value The System.Decimal data type has defined the format string C so that it returns a string representing currency. You can also define custom formatting schemes for the classes you create. In the next task, you'll add two custom formatting options to the SortablePoint class. The first, a long option indicated by L, prints the point as (x, y). The second, a short option indicated by S, prints the point as x y. You'll define three overloads of the ToString method to provide consistent formatting behavior for the SortablePoint class. The three overloads are described in the following table.
Listing 2.26 shows two equivalent data contracts. The first contract is exposed by the service the second class is described by the client. The two are equivalent and generate identical XML Schema Definitions. In the service, by default, WCF will order the XML elements alphabetically so the second schema forces the order to be alphabetical. Because of the Name StockPriceSvc and Name Currency attributes placed on the DataContract and DataMember respectively, the XSD generated in the second contract is identical to the first. DataMember public string Currency DataMember(0rder lj Name Currency ) public string Money
Currency In Visual Basic 6, the Currency data type stores a 64-bit number in integer format, but inserts a decimal point in the value at the fourth position. Also in VB 6, although you cannot declare a variable of type Decimal, the Variant type supports a Decimal type, which stores a 96-bit integer value with a moving decimal point. Visual Basic .NET abandons the Currency type in favor of using only the Decimal data type. Decimal offers more accuracy and the CLR supports Decimal directly.
If you coded the application as discussed so far, you will see there is still a problem with the data binding for the currency type text boxes. When you type in a new country name in the From Country or To Country text box and then press Tab, the flag for the country entered will be displayed. However, the currency type text box won't be updated unless you page to another record and then page back using the binding navigator. This problem is caused by the way a data row works when you edit the data contained in it. Getting back to the problem with the currency type text boxes on the BindingEvents sample's form, when a user enters a new country name and tabs to another control, the currency type doesn't update because when you set the CountryFromID or CountryTolD column value in the Parse event handler for the text box, you have made a transient programmatic change to that row. Until the change is committed with a call to EndEdit, other controls bound to that same property won't be...
The Decimal type holds decimal numbers with a precision of 28 significant decimal digits. Its purpose is to represent and manipulate decimal numbers without the rounding errors of the Single and Double types. The Decimal type replaces Visual Basic 6's Currency type. The underlying .NET type is System.Decimal.
ActiveReports allows you to set formatting strings for date, time, currency, and other numeric values using the OutputFormat property on the textbox control. The OutputFormat dialog also allows you to select international currency values and select from various built-in string expressions.
It is often useful for a client application to be able to call a method that is implemented on a remote server. Sometimes the method uses volatile information that is stored on the remote server (for example, a method that returns the current currency exchange that corresponds to a given currency). At other times, the developer wants to be able to upgrade the methods implementation without having to redeploy all the applications that use it.
Note When a format specifier includes symbols that vary by culture, such as the currency symbol included by the C and c formats, a formatting object supplies the actual charac-M ters used in a string representation of a numeric value. For example, a formatting object N may supply for the currency symbol. The formatting object for system-supplied
With the Hashtable class, you can dynamically add and remove elements without re-indexing. The following code example creates a new instance of the Hashtable class, named currency. It adds three key value pairs and retrieves one of these values by key. Console.Write( US Currency 0 , currencies( US )) Console.Write( US Currency 0 , currencies( US ))
Decimal has a set of arithmetic and logical operators, and also a range of methods to let you perform arithmetic, such as Add(), Subtract(), Multiply ) and Divide(), Mod(), Floor(), and Round(). It is recommended that Decimal be used to replace the older VB Currency type.
Let's see how the CompareValidator control is used. This control compares the value entered in a control with the value in another control or a specific value. You can compare these values by using any operator available with the control, such as Equal, NotEqual, GreaterThan, and LessThan. ASP.NET enables you to compare values of different types such as String, Integer, Double, Date, and Currency. Table 23-6 displays some of the common properties of the CompareValidator control. Currency,
Private Sub Page_PreRender(ByVal sender As Object, _ ByVal e As System.EventArgs) Handles MyBase.PreRender ' Display the culture's native name in the heading. head1.InnerHtml ' Display Date, Currency, and Numeric strings formatted for the culture. Label1.Text DateTime.Now.ToString( F ) Label2.Text 1234567890.ToString( C ) Label3.Text 1234567890.ToString( N ) End Sub
In a Windows Form application, the data-binding layer manages navigation through records in a data source. The CurrencyManager object associated with a table or view in a DataSet includes a Position property that can be used to navigate through data. Because the DataSet can contain multiple data sources, or because the controls on a form can be bound to two or more data lists, the form can have multiple currency managers. To find a record in a Windows Form, set the Position property of the CurrencyManager object for the bound data to the record position where you would like to go. CurrencyManager object Private myCM As CurrencyManager Private Sub BindContro1(myTab1e As DataTable) TextBoxl.DataBindings.Add( Text , myTable, CompanyName ) myCM CType(Me.BindingContext(myTab1e), CurrencyManager) myCM.Position 0 End Sub
The Format function returns a string, formatted as specified in the parameters in the function. Here, the formatting is as currency, but there are other predefined formats such as date and time. Additionally, you can create user-defined formats, such as changing a string of nine digits ( 123456789 ) into a Social Security number ( 123-45-6789 ). The first parameter of the Format function is the result of the multiplication of the number of units by the cost per units. The second parameter specifies the type of formatting (currency in this case). Table 7-1 lists the predefined numeric formats that can be specified in the second parameter (the symbol that specifies the type of formatting) Currency, C, or c
Given an instance of a char, you can call the static GetunicodeCategory method, which returns a value of the system.Globalization.unicodeCategory enumerated type. This value indicates whether the character is a control character, a currency symbol, a lowercase letter, an uppercase letter, a punctuation character, a math symbol, and so on (as defined by the Unicode 3.0 standard). To ease developing, the char type also offers several static methods, such as IsDigit, IsLetter, IsWhitespace, IsUpper, IsLower, IsPunctuation, IsLetter-OrDigit, Iscontrol, IsNumber, Isseparator, Issurrogate, and Issymbol. All these methods call Getunicodecategory internally and simply return true or false. Note that all these methods take either a single character for a parameter or a string and the index of a character within the string as parameters.
As shown in the above example, attributes provide additional information about a given element. Attributes can only exist within the context of an element that they give additional information about - they cannot contain child elements of their own. Attributes can be defined as any of the above listed primitive XML data types, or derived simple types such as a Currency type.
Just as there are several types to store integer values, there are three implementations of value types to store real number values, shown in Table 2-3. The Single and Double types work the same way in Visual Basic .NET as they did in Visual Basic 6.0. The difference is the Visual Basic 6.0 Currency type (which was a specialized version of a Double type), is now obsolete it was replaced by the Decimal value type for very large real numbers. Currency Decimal
The following example demonstrates when the custom interop marshaling must be used to stay compatible with a component that is not upgraded to Visual Basic 6.0. The original application has a COM class named Converter that defines the function ConvertCurrency that receives and returns values with the Currency Visual Basic 6.0 data type. This function is used by the rest of the application to perform financial calculations. The original declaration of ConvertCurrency is shown here. Public Function ConvertCurrency(amount As Currency, curFrom As String, _ curTo As String) As Currency ConvertCurrency amount * GetConversionFactor(curFrom, curTo) End Function Dim res As Currency Dim amount As Currency amount GetInitia1Amount() ByRef amount As Decimal _ ByRef curFrom As String, ByRef curTo As String) _ As Decimal ConvertCurrency amount * _ The MarshalAsAttribute attribute indicates that one of the function parameters and the function return value must be marshaled as a COM currency data type...
Another common requirement is the need to be able to change the current record in a set of data programmatically, or in response to a user interaction that is outside of a data grid. In .NET 1 .X, the way to do this was rather obscure you had to obtain a reference to the CurrencyManager object for the data source you were working with, and then had to update thBosition property on that object to change the current record CurrencyManager currMgr as CurrencyManager currMgr.Position++ This mechanism still exists for backward compatibility and still works. However, as mentioned earlier, you should always favor binding your data-bound controls to a binding source. If you do so, the binding source itself contains a currency manager, and it exposes an easy-to-use API for controlling the current record position within the underlying data source.
Use these two types to store currency amounts. Both types use four fractional digits. The money type uses eight bytes and can represent amounts in the range 922,337,203,685,477.5807 to 922,337,203,685,377.5807. The smallmoney type uses four bytes and can represent amounts in the range -214,748.3648 to 214,748.3647.
The class NumberFormatInfo provides methods and properties that assist with the formatting of numeric values according to culture. For example, the property Curren-cySymbol returns the currency symbol in the culture associated with a particular NumberFormatInfo object instance. You fetch the NumberFormatInfo for the calling thread's current culture via the static property CurrentInfo, or you can create them directly via the class constructor. The NumberFormatInfo class implements the interface System.IFormatProvider, which returns the proper number format pattern according to the culture for use in string formatting. You pass the NumberFormatInfo to the method ToString when you want to format a number. The enumeration NumberStyles customizes how the Parse methods of individual numeric types (for example, Int32.Parse) parse a string, for example, whether or not to allow an exponent.
The automation currency data type presents something of a problem because it is defined as a 64-bit integer data type and is scaled by 10,000 to give four decimal places and 15 digits to the left. The problem occurs when you are marshaling a currency value from the managed world to the unmanaged world, particularly if the conversion is done through a variant or Object parameter, because you need to indicate that the data you pass to such a method is the automation type vt_cy, and not vt_r8 (if you use a managed double type) or vt_i8 (if you use a managed long type). The solution lies in the framework class CurrencyWrapper. When this class is passed as a parameter, the marshaler knows that the data type is currency and hence ensures that the variant value is initialized accordingly account.CreditAccount(new CurrencyWrapper(cheque))
The StatusBar control is used to display brief information throughout the life of the application. This information should never it. This information should also be kept to a minimum to prevent a cluttered interface. Some possible status bar information i Information about the application mode or operating context. For example, if your application can be run by r user level (e.g., Administrator Mode). Similarly, a financial application might provide a label indicating U.S. Currency Information about the application status. For example, a database application might start by displaying Ready o database. This technique avoids stalling advanced users with a confirmation window where they need to click an O Information about a background process. For example, Microsoft Word provides some information about print o Information about the current document. For example, most word processors use a status bar to display the cu display ancillary information like the total number of files in a...
Currency C3 Currency C3 3.142 Exponential E3 3.142E+000 Fixed-Point F3 3.142 General G3 3.14 Number N3 3.142 If you go into the Control Panel and invoke the Regional and Language Options applet, you can change some settings for example, the currency symbol and the thousands separator that affect how ToString displays the number. By default, ToString uses the regional settings, but this behavior may be undesirable in some cases. You might want to display currency in dollars or euros regardless of the user's regional settings. To customize the formatting of numbers by ToString, you need an instance of the NumberFormatInfo class. If you look at the properties of this class, you'll see stuff like CurrencySymbol, CurrencyDecimal-Separator, and PercentSymbol. All these properties are settable and gettable. This means that you can create an object of type Number-FormatInfo, set the properties to whatever you want, and then pass that object to ToString to get the desired result....
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