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Chapter 5: Event-Based Programming
In this chapter, we explore the intricacies of working with server control events.
Using the Pager Control on a Web Form
The Pager Event Bubbling Web Form demonstrates the Pager control in both its button and hyperlink display motifs. A single label represents the PageCommand activity generated by the two controls. The first request for the page appears in the browser, as shown in Figure 5-18. Listings 5 17 and 5-18 provide the .aspx and code-behind files for this Web Form.
Figure 5-18. The Pager Event Bubbling Web Form rendering its first request
Listing 5-17. The Pager Event Bubbling Web Form .aspx Page File
<%@ Register TagPrefix="apress" Namespace="ControlsBookLib.Ch05"
Assembly="ControlsBookLib" %>
<%@ Page language="c#" Codebehind="PagerEventBubbling.aspx.cs"
AutoEventWireup="false"
Inherits="ControlsBookWeb.Ch05.PagerEventBubbling" %>
<%@ Register TagPrefix="apressUC" TagName="ControlsBookHeader
Src="..\ControlsBookHeader.ascx" %>
<%@ Register TagPrefix="apressUC" TagName="ControlsBookFooter"
Src="..\ControlsBookFooter.ascx" %>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" >
<HTML>
<HEAD>
<title>Ch05 Pager Event Bubbling</title>
<meta name="GENERATOR" Content="Microsoft Visual Studio 7.0">
<meta name="CODE_LANGUAGE" Content="C#">
<meta name="vs_defaultClientScript" content="JavaScript">
<meta name="vs_targetSchema"
content="http://schemas.microsoft.com/intellisense/ie5">
</HEAD>
<body MS_POSITIONING="FlowLayout">
<form id="PagerEventBubbling" method="post" runat="server">
<apressUC:ControlsBookHeader id="Header" runat="server" ChapterNumber="5"
ChapterTitle="Event-based Programming" />
<h3>Ch05 Pager Event Bubbling</h3>
<apress:pager id="pager1" display="button" runat="server"></apress:pager><br>
<br>
<h3>Direction: <asp:Label ID="DirectionLabel"
Runat="server"></asp:Label></h3>
<apress:pager id="pager2" display="hyperlink"
runat="server"></apress:pager><br>
<br>
<apressUC:ControlsBookFooter id="Footer" runat="server" />
</form>
</body>
</HTML>
Listing 5-18. The Pager Event Bubbling Web Form Code-Behind Class File
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 ControlsBookWeb.Ch05
{
public class PagerEventBubbling : System.Web.UI.Page
{
protected System.Web.UI.WebControls.Label DirectionLabel;
protected ControlsBookLib.Ch05.Pager pager1;
protected ControlsBookLib.Ch05.Pager pager2;
private void Page_Load(object sender, System.EventArgs e)
{
DirectionLabel.Text = "<none>";
}
#region Web Form Designer generated code
override protected void OnInit(EventArgs e)
{
//
// CODEGEN: This call is required by the ASP.NET Web Form Designer.
//
InitializeComponent();
base.OnInit(e);
}
/// <summary>
/// Required method for Designer support - do not modify
/// the contents of this method with the code editor.
/// </summary>
private void InitializeComponent()
{
this.pager1.PageCommand +=
new ControlsBookLib.Ch05.PageCommandEventHandler(this.Pagers_PageCommand);
this.pager2.PageCommand +=
new ControlsBookLib.Ch05.PageCommandEventHandler(this.Pagers_PageCommand);
this.Load += new System.EventHandler(this.Page_Load);
}
#endregion
private void Pagers_PageCommand(object o,
ControlsBookLib.Ch05.PageCommandEventArgs pce)
{
DirectionLabel.Text =
Enum.GetName(typeof(ControlsBookLib.Ch05.PageDirection),
pce.Direction);
}
}
}
The Pager controls are wired to the same event handler in the code-behind class named Pagers_PageCommand in the InitializeComponent method of the Web Form:
private void InitializeComponent()
{
this.pager1.PageCommand += new
ControlsBookLib.Ch05.PageCommandEventHandler(this.Pagers_PageCommand);
this.pager2.PageCommand += new
ControlsBookLib.Ch05.PageCommandEventHandler(this.Pagers_PageCommand);
this.Load += new System.EventHandler(this.Page_Load);
}
Pagers_PageCommand has an all-important second parameter of type
PageCommandEventArgs. We use it along with the System.Enum class's static GetName
method to produce a textual representation of the PageDirection enumeration value
for display in the DirectionLabel Text property:
private void Pagers_PageCommand(object o, C
ontrolsBookLib.Ch05.PageCommandEventArgs pce)
{
DirectionLabel.Text =
Enum.GetName(typeof(ControlsBookLib.Ch05.PageDirection),
pce.Direction);
}
Click the Left button of the top Pager control to verify that it is working. The result should look something like Figure 5-19.
Figure 5-19. The Page Event Bubbling Web Form after clicking the Left hyperlink button
Try the Right button with the bottom Pager that is in a hyperlink form and you should get output similar to Figure 5-20.
Figure 5-20. The Page Event Bubbling Web Form after clicking the Right hyperlink button
A snippet from the rendered HTML shows that the pager1 and pager2 Pager controls from the Pager Event Bubbling Web Form have their child controls identified in a nested fashion due to the INamingContainer interface with ASP.NET generating the UniqueID property:
<INPUT type="submit" name="pager1:buttonLeft" id="pager1:buttonLeft"
value="< Left"/>
<INPUT type="submit" name="pager1:buttonRight" id="pager1:buttonRight"
value="Right >"
<A href="javascript:__doPostBack('pager2:buttonLeft','')">< Left
</A> <A href="javascript:__doPostBack('pager2:buttonRight','')">
Right ></A></td></tr></table><br>
In the final section of this chapter, we review the control life cycle, which provides orderly processing to the busy life of server controls.