Professional ASP.NET 3.5 in C# and Visual Basic Part 42 ppt

Evjen c07.tex V2 - 01/28/2008 2:01pm Page 365 Chapter 7: Data Binding in ASP.NET 3.5 < asp:Label ID="CountryLabel" Runat="server" Text=’ < %# Bind("Country") % > ’ > < /asp:Label >< /td > < td style="width: 100px" >< /td > < td style="width: 100px" > Phone: < asp:Label ID="PhoneLabel" Runat="server" Text=’ < %# Bind("Phone") % > ’ > < /asp:Label >< br / > Fax: < asp:Label ID="FaxLabel" Runat="server" Text=’ < %# Bind("Fax") % > ’ > < /asp:Label >< br / > < /td > < /tr >< /table > < asp:Button ID="Button1" Runat="server" Text="Button" CommandName="edit" / > < /td > < /tr >< /table > < /ItemTemplate > < /asp:FormView > < asp:SqlDataSource ID="SqlDataSource1" Runat="server" SelectCommand="SELECT * FROM [Customers]" ConnectionString=" < %$ ConnectionStrings:AppConnectionString1 % > " > < /asp:SqlDataSource > < /div > < /form > < /body > < /html > Other Databound Controls ASP.NET 1.0/1.1 contained many other controls that could be bound to data sources. ASP.NET 2.0 retained those controls, enhanced some, and added several additional bound controls to the toolbox ASP.NET 3.5 continues to include these controls in its toolbox. DropDownList, ListBox, RadioButtonList, and CheckBoxList Although the DropDownList, ListBox, and CheckBoxList controls largely remained the same from ASP.NET 1.0/1.1 to ASP.NET 2.0, several new properties that you might find useful were added. In addi- tion, ASP.NET 2.0 added new RadioButtonList and BulletedList controls. All of these controls remain the same in ASP.NET 3.5. One of the new properties available in all these controls is the AppendDataBoundItems property. Setting this property to True tells the DropDownList control to append data-bound list items to any exist- ing statically declared items, rather then overwriting them as the ASP.NET 1.0/1.1 version would have done. Another useful new property available to all these controls is the DataTextFormatString , which allows you to specify a string format for the display text of the DropDownList items. 365 Evjen c07.tex V2 - 01/28/2008 2:01pm Page 366 Chapter 7: Data Binding in ASP.NET 3.5 TreeView Another control included in the ASP.NET toolbox is the TreeView control. Because the TreeView can display only hierarchical data, it can be bound only to the XmlDataSource and the SiteMapDataSource controls. Listing 7-59 shows a sample SiteMap file you can use for your SiteMapDataSource control. Listing 7-59: A SiteMap file for your samples < siteMap > < siteMapNode url="page3.aspx" title="Home" description="" roles="" > < siteMapNode url="page2.aspx" title="Content" description="" roles="" / > < siteMapNode url="page4.aspx" title="Links" description="" roles="" / > < siteMapNode url="page1.aspx" title="Comments" description="" roles="" / > < /siteMapNode > < /siteMap > Listing 7-60 shows how you can bind a TreeView control to a SiteMapDataSource control to generate navigation for your Web site. Listing 7-60: Using the TreeView with a SqlDataSource control < %@ Page Language="C#" % > < html xmlns="http://www.w3.org/1999/xhtml" > < head runat="server" > < title > Using the TreeView control < /title > < /head > < body > < form id="form1" runat="server" > < div > < asp:TreeView ID="TreeView1" Runat="server" DataSourceID="SiteMapDataSource1" > < /asp:TreeView > < asp:SiteMapDataSource ID="SiteMapDataSource1" Runat="server" / > < /div > < /form > < /body > < /html > Ad Rotator The familiar AdRotator control was greatly enhanced in ASP.NET 2.0. Y ou can see the control by using the SqlDataSource or XmlDataSource controls. Listing 7-61 shows an example of binding the AdRo- tator to a SqlDataSource control. Listing 7-61: Using the AdRotator with a SqlDataSource control < asp:AdRotator ID="AdRotator1" runat="server" DataSourceId="SqlDataSource1" AlternateTextField="AlternateTF" ImageUrlField="Image" NavigateUrlField="NavigateUrl" / > For more information on the Ad Rotator control, see Chapter 5. 366 Evjen c07.tex V2 - 01/28/2008 2:01pm Page 367 Chapter 7: Data Binding in ASP.NET 3.5 Menu The last control in this section is the new Menu control. Like the TreeView control, it is capable of displaying hierarchical data in a vertical pop-out style menu. Also like the TreeView control, it can be bound only to the XmlDataSource and the SiteMapDataSource controls. Listing 7-62 shows how you can use the same SiteMap data used earlier in the TreeView control sample, and modify it to display using the new Menu control. Listing 7-62: Using the Menu control with a SiteMap < %@ Page Language="C#" % > < html xmlns="http://www.w3.org/1999/xhtml" > < head runat="server" > < title > Using the Menu control < /title > < /head > < body > < form id="form1" runat="server" > < div > < asp:Menu ID="Menu1" Runat="server" DataSourceID="SiteMapDataSource1" > < /asp:Menu > < asp:SiteMapDataSource ID="SiteMapDataSource1" Runat="server" / > < /div > < /form > < /body > < /html > For more information on using t he Menu control, see Chapter 14. Inline Data-Binding Syntax Another feature of data binding in ASP.NET is inline data-binding syntax. Inline syntax in ASP.NET 1.0/1.1 was primarily relegated to templated controls such as the DataList or the Repeater controls, and even then it was sometimes difficult and confusing to make it work as you wanted it to. In ASP.NET 1.0/1.1, if you needed to use inline data binding, you might have created something like the procedure shown in Listing 7-63. Listing 7-63: Using DataBinders in ASP.NET 1.0 < asp:Repeater id=Repeater1 runat="server" > < HeaderTemplate > < table > < /HeaderTemplate > < ItemTemplate > < tr > < td > < %# Container.DataItem("Name") % >< BR/ > < %# Container.DataItem("Department") % >< BR/ > < %# DataBinder.Eval( Container.DataItem, "HireDate", "{0:mm dd yyyy}") % >< BR/ > < /td > Continued 367 Evjen c07.tex V2 - 01/28/2008 2:01pm Page 368 Chapter 7: Data Binding in ASP.NET 3.5 < /tr > < /ItemTemplate > < FooterTemplate > < /table > < /FooterTemplate > < /asp:Repeater > As you can see in this sample, you are using a Repeater control to display a series of employees. Because the Repeater control is a templated control, you use data binding to output the employee-specific data in the proper location of the template. Using the Eval method also allows you to provide formatting information such as Date or Currency formatting at render-time. In later versions of ASP.NET, including 3.5, the concept of inline data binding remains basically the same, but you are given a simpler syntax and several powerful new binding tools to use. Data-Binding Syntax Changes ASP.NET contains three different ways to perform data binding. First, you can continue to use the exist- ing method of binding, using the Container.DataItem syntax: < %# Container.DataItem("Name") % > This is good because it means you w on’t have to change your existing Web pages if you are migrating from prior versions of ASP.NET. But if you are creating new Web pages, you should probably use the simplest form of binding, using the Eval method directly: < %# Eval("Name") % > You can also continue to format data using the formatter overload of the Eval method: < %# Eval("HireDate", "{0:mm dd yyyy}" ) % > In addition to these changes, ASP.NET includes a form of data binding called two-way data binding.In ASP.NET 1.0/1.1, using the data-binding syntax was essentially a read-only form of accessing data. Since the introduction of ASP.NET 2.0, two-way data binding has allowed you to support both read and write operations for bound data. This is done using the Bind method, which, other than using a different method name, works just like the Eval method: < %# Bind("Name") % > The new Bind method should be used in new controls such as the GridView, DetailsView, or FormView, where auto-updates to the data source are implemented. When working with the data binding statements, remember that anything between the < %# % > delimiters is treated as an expression. This is important because it gives you additional functionality when data binding. For example, you could append additional data: < %# "Foo " + Eval("Name") % > Or you can even pass the evaluated value to a method: < %# DoSomeProcess( Eval("Name") )% > 368 Evjen c07.tex V2 - 01/28/2008 2:01pm Page 369 Chapter 7: Data Binding in ASP.NET 3.5 XML Data Binding Because XML is becoming ever more prevalent in applications, ASP.NET also includes several ways to bind specifically to XML data sources. These new data binding expressions give you powerful ways of working with the hierarchical format of XML. Additionally, except for the different method names, these binding methods work exactly the same as the Eval and Bind methods discussed earlier. These binders should be used when you are using the XmlDataSource control. The first binding format that uses the XPathBinder class is shown in the following code: < % XPathBinder.Eval(Container.DataItem, "employees/employee/Name") % > Notice that rather than specifying a column name as in the Eval method, the XPathBinder binds the result of an XPath query. Like the standard Eval expression, the XPath data binding expression also has a shorthand format: < % XPath("employees/employee/Name") % > Also, like the Eval method, the XPath data binding expression supports applying formatting to the data: < % XPath("employees/employee/HireDate", "{0:mm dd yyyy}") % > The XPathBinder returns a single node using the XPath query provided. Should you want to return multiple nodes from the XmlDataSource Control, you can use the class’s Select method.Thismethod returns a list of nodes that match the supplied XPath query: < % XPathBinder.Select(Container.DataItem,"employees/employee") % > Or use the shorthand syntax: < % XpathSelect("employees/employee") % > Expressions and Expression Builders Finally, ASP.NET introduces the concept of expressions and expression builders. Expressions are state- ments that a re parsed by ASP.NET at runtime in order to return a data value. ASP.NET automatically uses expressions to do things like retrieve the database connection string when it parses the SqlData- Source control, so you may have already seen these statements in your pages. An example of the connec- tion string Expression is shown in Listing 7-64. Listing 7-64: A connection string Expression < asp:SqlDataSource ID="SqlDataSource1" runat="server" ConnectionString=" < %$ ConnectionStrings:NorthwindConnectionString % > " SelectCommand="SELECT * FROM Customers" >< /asp:SqlDataSource > When ASP.NET is attempting to parse an ASP.NET Web page, it looks for expressions contained in the < %$ % >delimiters. This indicates to ASP.NET that this is an expression to be parsed. As shown in the previous listing, it attempts to locate the NorthwindConnectionString value from the web.config file. ASP.NET knows to do this because of the ConnectionStrings expression prefix, which tells ASP.NET to use the ConnectionStringsExpressionBuilder class to parse the expression. 369 Evjen c07.tex V2 - 01/28/2008 2:01pm Page 370 Chapter 7: Data Binding in ASP.NET 3.5 ASP.NET includes several expression builders, including one for retrieving values from the AppSet- tings section of web.config : one for retrieving ConnectionStrings as shown in Listing 7-64, and one for retrieving localized resource file values. Listings 7-65 and 7-66 demonstrate using the AppSettingsEx- pressionBuilder and the ResourceExpressionBuilder . Listing 7-65: Using AppSettingsExpressionBuilder < asp:Label runat="server" ID="lblAppSettings" Text=" < %$ AppSettings: LabelText % > " >< /asp:Label > Listing 7-66: Using ResourceExpressionBuilder < asp:Label runat="server" ID="lblResource" Text=" < %$ Resources: TEST % > " >< /asp:Label > In addition to using the expression builder classes, you can also create your own expressions by deriving aclassfromthe System.Web.Compilation.ExpressionBuilder base class. This base class provides you with the overridable methods you need to implement if you want ASP.NET to parse your expression properly. Listing 7-67 shows a simple custom expression builder. Listing 7-67: Using a simple custom expression builder VB Imports System; Imports System.CodeDom; Imports System.Web.Compilation; Imports System.Web.UI; < ExpressionPrefix("MyCustomExpression") > < ExpressionEditor("MyCustomExpressionEditor") > Public Class MyCustomExpression Inherits ExpressionBuilder Public Overrides Function GetCodeExpression(ByVal entry As BoundPropertyEntry, ByVal parsedData As object, ByVal context As ExpressionBuilderContext) As System.CodeDom.CodeExpression Return New CodeCastExpression("Int64", new CodePrimitiveExpression(1000)) End Function End Class C# using System; using System.CodeDom; using System.Web.Compilation; using System.Web.UI; [ExpressionPrefix("MyCustomExpression")] [ExpressionEditor("MyCustomExpressionEditor")] public class MyCustomExpression : ExpressionBuilder { public override System.CodeDom.CodeExpression 370 Evjen c07.tex V2 - 01/28/2008 2:01pm Page 371 Chapter 7: Data Binding in ASP.NET 3.5 GetCodeExpression(BoundPropertyEntry entry, object parsedData, ExpressionBuilderContext context) { return new CodeCastExpression("Int64", new CodePrimitiveExpression(1000)); } } In examining this sample, notice several items. First, you have derived the MyCustomExpression class from ExpressionBuilder as I discussed earlier. Second, you have overridden the GetCodeExpression method. This method supplies you with several parameters that can be helpful in executing this method, and it returns a CodeExpression object to ASP.NET that it can execute at runtime to retrieve the data value. The CodeExpression class is a base class in .NET’s CodeDom infrastructure. Classes that are derived from the CodeExpression class provide abstracted ways of generating .NET code, whether VB or C#. This CodeDom infrastructure is what helps you create and run code dynamically at runtime. The BoundPropertyEntry parameter entry tells you exactly which property the expression is bound to. For example, in Listings 7-58 and 7-59, the Label’s Text property is bound to the AppSettings and Resources expressions. The object parameter parsedData contains any data that was parsed and returned by the ParseExpression method that you see later on in the chapter. Finally, the ExpressionBuilder- Context parameter context allows you to reference the virtual path or templated control associated with the expression. In the body of the GetCodeExpression method, you are creating a new CodeCastExpression object, whichisaclassderivedfromthe CodeExpression base class. The CodeCastExpression tells .NET to generate the appropriate code to execute a cast from one data type to another. In this case, you are casting the value 1000 to an Int64 datatype. When .NET executes the CodeCastExpression ,itis(inasense) writing the C# code ((long)(1000)), or (if your application was written in VB) CType(1000,Long). Note that a wide variety of classes derive from the CodeExpression class that you can use to generate your final code expression. The final lines to note are the two attributes that have been added to the class. The ExpressionPrefix and ExpressionEditor attributes help .NET figure out that this class should be used as an expression, and they also help .NET locate the proper expression builder class when it comes time to parse the expression. After you have created your expression builder class, you let .NET know about it. You do this by adding an expressionBuilders node to the compilation node in your web.config file. Notice that the value of the ExpressionPrefix is added to the expressionBuilder to help ASP.NET locate the appropriate expression builder class at runtime. < compilation debug="true" strict="false" explicit="true" > < expressionBuilders > < add expressionPrefix="MyCustomExpression" type="MyCustomExpression"/ > < /expressionBuilders > < /compilation > The GetCodeExpression method is not the only member available for overriding in the Expression- Builder class. Several other useful members include the ParseExpression , SupportsEvaluate ,and EvaluateExpression methods. 371 Evjen c07.tex V2 - 01/28/2008 2:01pm Page 372 Chapter 7: Data Binding in ASP.NET 3.5 The ParseExpression method lets you pass parsed expression data into the GetCodeExpression method. For example, in Listing 7-60, the CodeCastExpression value 1000 was hard-coded. If, however, you want to allow a developer to pass that value in as part of the expression, you simply use the ParseExpression method as shown in Listing 7-68 Listing 7-68: Using ParseExpression VB Imports System; Imports System.CodeDom; Imports System.Web.Compilation; Imports System.Web.UI; < ExpressionPrefix("MyCustomExpression") > < ExpressionEditor("MyCustomExpressionEditor") > Public Class MyCustomExpression Inherits ExpressionBuilder Public Overrides Function GetCodeExpression(ByVal entry As BoundPropertyEntry, ByVal parsedData As object, ByVal context As ExpressionBuilderContext) As System.CodeDom.CodeExpression Return New CodeCastExpression("Int64", new CodePrimitiveExpression(passedData)) End Function Public Overrides Function ParseExpression (ByVal expression As String, ByVal propertyType As Type, ByVal context As ExpressionBuilderContext) As Object Return expression End Function End Class C# using System; using System.CodeDom; using System.Web.Compilation; using System.Web.UI; [ExpressionPrefix("MyCustomExpression")] [ExpressionEditor("MyCustomExpressionEditor")] public class MyCustomExpression : ExpressionBuilder { public override System.CodeDom.CodeExpression GetCodeExpression(BoundPropertyEntry entry, object parsedData, ExpressionBuilderContext context) { return new CodeCastExpression("Int64", new CodePrimitiveExpression(parsedData)); } 372 Evjen c07.tex V2 - 01/28/2008 2:01pm Page 373 Chapter 7: Data Binding in ASP.NET 3.5 public override object ParseExpression (string expression, Type propertyType, ExpressionBuilderContext context) { return expression; } } The last two ExpressionBuilder overrides to examine are the SupportsEvaluate and EvaluateExpres- sion members. You need to override these methods if you are running your Web site in a no-compile scenario (you have specified compilationMode = "never" in your @Page directive). The SupportEvalu- ate property returns a Boolean indicating to ASP.NET whether this expression can be evaluated while a page is executing in no-compile mode. If True is returned and the page is executing in no-compile mo de, the EvaluateExpression method is used to return the data value rather than the GetCodeExpression method. The EvaluateExpression returns an object representing the data value. See Listing 7-69. Listing 7-69: Overriding SupportsEvaluate and EvaluateExpression VB Imports System; Imports System.CodeDom; Imports System.Web.Compilation; Imports System.Web.UI; < ExpressionPrefix("MyCustomExpression") > < ExpressionEditor("MyCustomExpressionEditor") > Public Class MyCustomExpression Inherits ExpressionBuilder Public Overrides Function GetCodeExpression(ByVal entry As BoundPropertyEntry, ByVal parsedData As object, ByVal context As ExpressionBuilderContext) As System.CodeDom.CodeExpression Return New CodeCastExpression("Int64", new CodePrimitiveExpression(pasedData)) End Function Public Overrides Function ParseExpression (ByVal expression As String, ByVal propertyType As Type, ByVal context As ExpressionBuilderContext) As Object Return expression End Function Public Overrides ReadOnly Property SupportsEvaluate as Boolean Get Return True End Get End Property Public Overrides Function EvaluateExpression(ByVal target As Object, ByVal Entry As BoundPropertyEntry, ByVal parsedData As Object, ByVal context As ExpressionBuilderContext) as Object Continued 373 Evjen c07.tex V2 - 01/28/2008 2:01pm Page 374 Chapter 7: Data Binding in ASP.NET 3.5 Return parsedData; End Function End Class C# using System; using System.CodeDom; using System.Web.Compilation; using System.Web.UI; [ExpressionPrefix("MyCustomExpression")] [ExpressionEditor("MyCustomExpression123Editor")] public class MyCustomExpression : ExpressionBuilder { public override System.CodeDom.CodeExpression GetCodeExpression(BoundPropertyEntry entry, object parsedData, ExpressionBuilderContext context) { return new CodeCastExpression("Int64", new CodePrimitiveExpression(parsedData)); } public override object ParseExpression (string expression, Type propertyType, ExpressionBuilderContext context) { return expression; } public override bool SupportsEvaluate { get { return true; } } public override object EvaluateExpression(object target, BoundPropertyEntry entry, object parsedData, ExpressionBuilderContext context) { return parsedData; } } As shown in Listing 7-69, you can simply return True from the SupportsEvaluate property if you want to override the EvaluateExpression method.Thenallyoudoisreturnanobjectfromthe EvaluateEx- pression method. 374 . / > < /div > < /form > < /body > < /html > For more information on using t he Menu control, see Chapter 14. Inline Data-Binding Syntax Another feature of data binding in ASP. NET is inline data-binding syntax. Inline syntax in ASP. NET 1.0/1.1. ASP. NET, including 3. 5, the concept of inline data binding remains basically the same, but you are given a simpler syntax and several powerful new binding tools to use. Data-Binding Syntax Changes ASP. NET. binding called two-way data binding .In ASP. NET 1.0/1.1, using the data-binding syntax was essentially a read-only form of accessing data. Since the introduction of ASP. NET 2.0, two-way data binding