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public string LabelStyle
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{ get { return labelStyle; } set { labelStyle = value; } }
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public LabelLocationCS LabelLocation { get { return labelLocation; } set { labelLocation = value; } }
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/// <summary> /// Render control to output parameter specified. /// </summary> /// <param name="output"> The HTML writer /// to write out to </param> protected override void Render(HtmlTextWriter output) {
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if ( labelStyle != null ) { output.Write("<Span Style=\""); output.Write(labelStyle); output.Write("\">"); output.Write(labelText); output.Write("</Span>"); } else { output.Write(labelText); } if ( labelLocation == LabelLocationCS.LabelAbove ) { output.RenderBeginTag(HtmlTextWriterTag.Br); output.RenderEndTag(); } base.Render(output); } } }
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You ll notice some minor differences between the two classes. The first difference is the three-slash (///) comment marker used for XML documentation. Using the XML documentation provided by Visual Studio as a starting point, you can add documentation on classes and class members that can be parsed out to create an XML file. The C# property syntax is also a little different from the Visual Basic .NET syntax, but it s similar enough that you shouldn t have any difficulty following the intent of the code. One characteristic of properties in both Visual Basic .NET and C# is that the access modifier (in Listings 6-6 and 6-7, Public) applies to both the Get and Set methods. This is an unfortunate limitation, but you can overcome it by providing a property with a Get method with one level of protection and then a separate nonproperty setter method with another level of protection, although this solution isn t ideal. For example, this fragment of a class allows all classes to read ReadOnlyText, but it provides a nonproperty setter method to
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allow the class to update the internal buffer that is returned as the ReadOnlyText property: private string _readOnlyText; public string ReadOnlyText { get { return _readOnlyText; } } private setReadOnlyText(string Value) { _readOnlyText=Value; } A more realistic example would be one in which the property isn t simply getting and setting an underlying field but is synthesizing the value in a more complex way. Note One difference between Visual Basic .NET properties and C# properties is that in Visual Basic .NET properties, the type of the property is present twice in the declaration of the property: once as the property is declared and once as the type of the Value parameters to the Set method. The C# syntax mentions the type only once, which is somewhat more convenient if during development you re changing the type of the parameter. The Render method in Listing 6-7 is similar to the Visual Basic .NET version in Listing 66, discounting obvious syntax differences between the two languages. One more significant difference between the two Render methods is the use of a different keyword to access the base implementation of the class. C# uses base, whereas Visual Basic .NET uses MyBase. A Composite Custom Control A composite custom control shares many of the benefits of user controls, and at the same time offers the benefits of normal custom controls. If you re a developer for an internal Internet or intranet site, the functional difference between a user control and a composite custom control isn t that great. However, if you need to distribute a component to other groups within your organization or if you re a third-party vendor planning to sell a component, the composite custom control offers tremendous advantages. First, it s completely compiled, with no .ascx file that must be exposed to the end user. Second, as a custom control, your component offers certain advantages within a design-time environment such as Visual Studio .NET. Caution One problem you might discover when you use a tool like Visual Studio .NET instead of something like Notepad is that the tool can sometimes add its own tool-specific restrictions or bugs. For example, in preparing this composite control example, I foolishly used the same name for the namespace and the class. In initial testing of a page generated using just Notepad, the control worked as expected. However, one of the points of this example is to show the support for custom controls within Visual Studio .NET. I followed all instructions and was able to get the control installed, yet try as I might, I kept getting this strange error: CS0103: The name __ctrl does not exist in the class or namespace ASP.WebForm1_aspx . I had no control named __ctrl, so I was puzzled. In the end, I discovered that the error was in the
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code Visual Studio .NET generated to create the control. Renaming the namespace solved the problem, but not before it cost me several hours I would rather have spent doing something else. One of the good things about ASP.NET is that it allows you to automate some of the more common and boring tasks, such as providing validation for text boxes. The problem is that even with automation it s still more work than most Visual Basic developers are used to. Rather than associating a Required Boolean with the text box control, you need to drop two controls on the form a text box and a validator and wire them up. An alternative technique is to create a composite custom control, combining both a required field validator and a text box in a single control, and then wire them up automatically. Listing 6-8 shows the code for a composite custom control named RequiredTextBox written in C#. This control requires that the user enter text into a text box. The control uses a text box control and a required field validator. Listing 6-8 RequiredTextBoxCs.cs, an example composite custom control
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using System; using System.IO; using System.Web.UI; using System.Web.UI.WebControls; using System.ComponentModel; using System.Collections; using System.Collections.Specialized; using System.Web.UI.Design;
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[ assembly:TagPrefix("MyControls","RequiredTextBox") ]
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namespace MyControls { /// <summary> /// Summary description for WebCustomControl1. /// </summary> ///
[DefaultProperty("Text"), ToolboxData(
"<{0}:RequiredTextBox runat=server></{0}:RequiredTextBox>"), Designer("MyControls.RequiredTextBoxDesigner, RequiredTextBox") ] public class RequiredTextBox : System.Web.UI.Control, INamingContainer {
[Bindable(true), Category("Appearance"), DefaultValue("Text")] public string Text { get {return (string)ViewState["text"]; } set {ViewState["text"] = value; } } [Bindable(false), Category("Validator")] public string ErrorMessage { get {return (string)ViewState["errorMessage"]; } set {ViewState["errorMessage"]= value; } } [Bindable(false), Category("Validator"), DefaultValue("")] public string ValidatorText { get {return (string)ViewState["validatorText"]; } set {ViewState["validatorText"]= value; } } [Bindable(false),
Category("Validator")] public System.Drawing.Color ValidatorColor { get { // This will throw an exception the first time. // An alternative would be to initialize this in // a constructor. try { return (System.Drawing.Color) ViewState["validatorColor"]; } catch (Exception e) { return System.Drawing.Color.Red; } } set {ViewState["validatorColor"]= value; } } protected override void CreateChildControls() { System.Web.UI.WebControls.TextBox textBox; System.Web.UI.WebControls.RequiredFieldValidator requiredValidator;
textBox=new TextBox(); textBox.ID=UniqueID; textBox.Text=this.Text;
requiredValidator=new RequiredFieldValidator();
requiredValidator.ErrorMessage=this.ErrorMessage; requiredValidator.ForeColor=this.ValidatorColor; requiredValidator.Text=this.ValidatorText; requiredValidator.ID=UniqueID + "Validator"; requiredValidator.ControlToValidate=textBox.ID;
Controls.Add(textBox); Controls.Add(new LiteralControl(" ")); Controls.Add(requiredValidator);
public class RequiredTextBoxDesigner : ControlDesigner { public RequiredTextBoxDesigner() { } public override string GetDesignTimeHtml() { RequiredTextBox rtb = (RequiredTextBox) Component;
StringWriter sw = new StringWriter(); HtmlTextWriter tw = new HtmlTextWriter(sw);
HyperLink placeholderLink = new HyperLink();
placeholderLink.Text="RequiredTextBox Designer"; placeholderLink.RenderControl(tw);
return sw.ToString(); } } }
The first thing to notice in Listing 6-8 is the inclusion of several namespaces I haven t previously used. System.IO and System.Web.UI.Design are both used to add designer support to the component. System.Web.UI.Design requires adding a reference to System.Design.dll to the project. This and all other system-supplied DLLs are located in the <windir>/Microsoft.NET/Framework/<version> directory. The attributes for the RequiredTextBox class are the defaults provided by Visual Studio .NET, with the addition of the Designer attribute, which will be described when we look at the designer in the section Enhancing Design-Time Support later in this chapter. The class implements INamingContainer, a marker interface that has no methods that need to be implemented. Implementing INamingContainer tells the framework that a new namespace should be created to ensure unique names within the application. Several properties are declared, and all are persisted in the ViewState rather than in class members. In the following get and set methods, notice that when the value is retrieved, it must be cast to the type expected: public string Text { get {return (string)ViewState["text"]; } set {ViewState["text"] = value; } } Several of the properties are related to the required field validator, and so I use the Category attribute to create a new category named Validator that will allow all the validator-related properties to be displayed together when properties are displayed in categories. The bulk of the work in the class is done within the CreateChildControls method. This method is called by the .NET Framework in preparation for posting back or rendering. This method actually creates the instances of the text box and required field validator controls. An additional method not used here can be handy when creating composite controls: EnsureChildControls. This method will check to see whether the child controls have been created, and if they haven t, it creates them. Within CreateChildControls, I first create the TextBox control, assign it a unique ID, and then set the Text property to the Text property of the composite control. To get the ID, I use the UniqueID property of Control, which gives me an ID I can use. The ID is required because I need to assign the ControlToValidate property of the RequiredFieldValidator control I create next. Once the RequiredFieldValidator instance is created, I assign appropriate properties from the main control. To set the RequiredFieldValidator ID, I use the UniqueID property with the literal Validator appended. C/C++ programmers will notice that a function call such as strcat isn t required. I simply use the + operator to combine the strings. After I ve created both major controls, I add them to the composite control, using the Add method of Controls. I also add a literal control between the text box and the validator, simply to provide some white space between the text box and the validator. LiteralControl is a class that represents HTML elements and text that doesn t need to be processed on the server. Once these controls are added, I can reference them using the Controls array, which is 1-based. In this example, the text box would be Controls[1], the literal control would be Controls[2], and the validator control would be Controls[3]. To use the Controls array, you generally need to cast the element of the array to the correct
type. For example, to get a usable reference to the text box control, you would use ((TextBox)Controls[1]).
Composition vs. Rendering When presented with the need to create a composite control, you have two options: composition or rendering. Composition allows you to create the individual objects, manipulate properties, and insert each of the objects into the final control. Rendering allows you just to emit arbitrary HTML code, formatted in whatever way is convenient. This example uses composition, a method that creates multiple server side controls that the ASP.NET framework will render for you. This is done in the CreateChildControls method. Another alternative is to use the Render method. Recall that I used the Render method earlier in this chapter with the CenteredLabel custom control. This same Render event can also be used for composite controls, though it becomes awkward with large numbers of controls, and there are additional tasks you must perform. When using the rendering option, rather than creating server controls where you can set properties, you need to create the code to render the HTML controls. This is similar to the way you created the noncomposite CenteredLabel control earlier in this chapter, but likely somewhat more complex because you might need to also have code to set up the relationship between the two controls. Next, there are two additional interfaces that you may need to implement, IPostBackEventHandler and IPostBackDataHandler. Finally, you need to override the Render method. The RequiredTextBox example isn t a good candidate for rendering because you d end up writing server-side code that would be quite a bit more complex than the code I m using for composition. You d have to manually handle the validation part of the control since all you could render would be HTML.
Installing a Control in Visual Studio .NET To install a control for use within a project in Visual Studio .NET, you have two options. First, you can manually copy the control to the bin folder for the project and manually add the @ Register tag to the form. This method isn t terribly onerous; however, if you re committed to using Visual Studio .NET, there s an easier way. To begin, open the project in which you ll be using the control. While in design mode on one of the Web Forms in the project, select the Toolbox tab where you want to add the control. Right-click the Toolbox, and choose Customize Toolbox on the shortcut menu. Select the .NET Framework Components tab in the Customize Toolbox dialog box, and click the Browse button. Navigate to the folder containing the assembly with the control you want to add, often in the bin folder under the project, or in the bin\Release folder for a C# project. Select the assembly, which is a file with a .dll extension. The control should show up in the list of controls on the .NET Framework Components tab. Make sure there s a check mark next to the control, as shown in Figure 6-6, and click OK in the Customize Toolbox dialog box.
Figure 6-6 : Adding the RequiredTextBox control to the Toolbox When you add the control to the Web Form for the first time, the following results will occur: The control s TagPrefix and Namespace attributes are added to the @ Register directive for the page. A tag for the control is added to the page. A reference to the control is added to the project. This has the effect of copying the assembly to the bin folder of the application. If applicable, the control s designer is loaded. The control is displayed in the designer. Of course, none of these tasks are particularly difficult, but anything that can be properly automated by the development environment is one less thing for the developer to worry about. In general, in the rest of this book, the components used in the examples will be added to the Toolbox. Figure 6-7 shows a simple form with a RequiredTextBox control dropped on it.
Figure 6-7 : The RequiredTextBox control in Visual Studio .NET designer Listing 6-9 shows the code for WebForm1.aspx, which uses the RequiredTextBox control. Listing 6-9 WebForm1.aspx, used to test the RequiredTextBox control
<%@ Register TagPrefix="requiredtextbox" Namespace="MyControls"
Assembly="RequiredTextBox" %> <%@ Page language="c#" Codebehind="WebForm1.aspx.cs" AutoEventWireup="false" Inherits="06_TestRequiredTextBox.WebForm1" %> <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" > <HTML> <HEAD> <meta name="GENERATOR" Content="Microsoft Visual Studio 7.0"> <meta name="CODE_LANGUAGE" Content="C#"> <meta name="vs_defaultClientScript" content="JavaScript (ECMAScript)"> <meta name="vs_targetSchema" content="http://schemas.microsoft.com/intellisense/ie5"> </HEAD> <body> <form id="Form1" method="post" runat="server"> <TABLE cellSpacing="1" cellPadding="1" width="600" border="0"> <TR height="100"> <TD width="50%" align="right"> <asp:Label id="Label1" runat="server"> Must Enter: </asp:Label> </TD> <TD>
<RequiredTextBox:RequiredTextBox id="RequiredTextBox1" runat="server" ErrorMessage="*"> </RequiredTextBox:RequiredTextBox> </TD> </TR> <TR> <TD colspan="2" align="middle"> <asp:Button Runat="server" Text="Submit" id="Button1"> </asp:Button> </TD> </TR> </TABLE> </form> </body> </HTML>
Listing 6-10 shows the code-behind file located in WebForm1.aspx.cs. Listing 6-10 WebForm1.aspx.cs C# code-behind file for the page to test the RequiredTextBox composite control
using System; using System.Collections; using System.ComponentModel; using System.Data; using System.Drawing;
using System.Web; using System.Web.SessionState; using System.Web.UI; using System.Web.UI.WebControls; using System.Web.UI.HtmlControls;
namespace 06_TestRequiredTextBox { /// <summary> /// Summary description for WebForm1. /// </summary> public class WebForm1 : System.Web.UI.Page { protected MyControls.RequiredTextBox RequiredTextBox1; protected System.Web.UI.WebControls.Button Button1; protected System.Web.UI.WebControls.Label Label1;
public WebForm1() { Page.Init += new System.EventHandler(Page_Init); }
private void Page_Load(object sender, System.EventArgs e) { // Put user code to initialize the page here. }
private void Page_Init(object sender, EventArgs e) { //
// CODEGEN: This call is required by // the ASP.NET Web Form Designer. // InitializeComponent(); }
#region Web Form Designer generated code /// <summary> /// Required method for Designer support - do not modify /// the contents of this method with the code editor. /// </summary> private void InitializeComponent() { this.Load += new System.EventHandler(this.Page_Load);
} #endregion } }
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