7: Control Development in a Partial Postback Environment ErrorHandler Component in .NET framework

Encoder GS1 - 13 in .NET framework 7: Control Development in a Partial Postback Environment ErrorHandler Component
7: Control Development in a Partial Postback Environment ErrorHandler Component
Paint GS1 - 13 In .NET
Using Barcode generator for ASP.NET Control to generate, create EAN-13 image in ASP.NET applications.
A good example of when we ll want to do this is when we have a component represented by a server control that we intend to be global to the application An example of this is the ErrorHandler component we created in 3, Components We intend that this component will be created once when the page initializes, will live throughout the page s life, and be disposed of when the page unloads However, if the ErrorHandler component is created by a related server control, which internally uses a ScriptComponentDescriptor, and that control is placed within an UpdatePanel, every time that UpdatePanel updates, our ErrorHandler component will be disposed of and re-created The re-creation of the ErrorHandler component won t cause errors itself, but if it s disposed of and then JavaScript code throws an error before it s re-created, the ErrorHandler component won t be around to handle that error Also, disposing of and re-creating it is a waste of processing and resources To start, let s assume that we have the ErrorHandler component s code available to us in a JavaScript le (Its full source is available in Appendix D, Client Error Handling Code ) We create an instance of the component using a related server control, which uses a ScriptComponentDescriptor Listing 722 shows the server control s code
Barcode Generator In .NET
Using Barcode generator for ASP.NET Control to generate, create bar code image in ASP.NET applications.
Listing 722 The ErrorHandler Server Control
Creating EAN-13 Supplement 5 In VS .NET
Using Barcode printer for VS .NET Control to generate, create EAN / UCC - 13 image in .NET framework applications.
using SystemCollectionsGeneric; using SystemWebUI; using System; namespace ErrorHandlerLibrary { public class ErrorHandler : ScriptControl { protected override IEnumerable<ScriptReference> GetScriptReferences() { yield return new ScriptReference("ErrorHandlerLibraryErrorHandlerjs", typeof(ErrorHandler)AssemblyFullName); } protected override IEnumerable<ScriptDescriptor> GetScriptDescriptors() {
Data Matrix Maker In VS .NET
Using Barcode generator for ASP.NET Control to generate, create ECC200 image in ASP.NET applications.
The Effe cts of a Partial Postback on Client Components
UPC Symbol Maker In .NET Framework
Using Barcode drawer for ASP.NET Control to generate, create UPC-A Supplement 2 image in ASP.NET applications.
ScriptComponentDescriptor scd = new ScriptComponentDescriptor("ErrorHandler"); scdID = "ErrorHandler"; yield return scd; } } }
Barcode Creator In VS .NET
Using Barcode printer for ASP.NET Control to generate, create bar code image in ASP.NET applications.
NOTE
UCC.EAN - 128 Maker In Visual Studio .NET
Using Barcode drawer for ASP.NET Control to generate, create EAN / UCC - 13 image in ASP.NET applications.
Abbreviated Version
Barcode Generator In .NET Framework
Using Barcode maker for ASP.NET Control to generate, create barcode image in ASP.NET applications.
Appendix D has the full version of the ErrorHandler s server control For brevity, we re just displaying the pertinent parts of it
Make Bar Code In Visual Studio .NET
Using Barcode maker for ASP.NET Control to generate, create barcode image in ASP.NET applications.
Next, we place our ErrorHandler server control inside an UpdatePanel, as shown in Listing 723
Industrial 2 Of 5 Creation In VS .NET
Using Barcode maker for ASP.NET Control to generate, create 2/5 Industrial image in ASP.NET applications.
Listing 723 The ErrorHandler Test Page
USS Code 39 Printer In Visual Basic .NET
Using Barcode generation for .NET Control to generate, create Code 39 Full ASCII image in Visual Studio .NET applications.
<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="ErrorHandleraspxcs" Inherits="_7ErrorHandler" %> <%@ Register Assembly="Controls" Namespace="Controls" TagPrefix="cc1" %> <html> <head runat="server"> <title>Error Handler Test Page</title> </head> <body> <form id="form1" runat="server"> <asp:ScriptManager ID="SM1" runat="server" /> <asp:UpdatePanel ID="UP1" runat="server" UpdateMode="Conditional"> <ContentTemplate> <cc1:ErrorHandler ID="ErrorHandler" runat="server" /> <asp:Button ID="tstButton" Text="Update" runat="server" /> </ContentTemplate> </asp:UpdatePanel> </form> </body> </html>
Encode Data Matrix ECC200 In VB.NET
Using Barcode drawer for VS .NET Control to generate, create DataMatrix image in .NET applications.
7: Control Development in a Partial Postback Environment
Encode Data Matrix 2d Barcode In Java
Using Barcode printer for Java Control to generate, create Data Matrix ECC200 image in Java applications.
As you might have guessed, every time we click the Update button, the ErrorHandler component is disposed of and re-created Figure 720 shows the initialization and disposal debug messages in the Visual Studio output window
Barcode Creator In VB.NET
Using Barcode drawer for Visual Studio .NET Control to generate, create bar code image in .NET framework applications.
Figure 720 ErrorHandler s initialization and disposal messages
Code 128 Code Set C Generator In Java
Using Barcode encoder for Java Control to generate, create Code 128B image in Java applications.
We can prevent this unwanted disposal and re-creation by not using a ScriptComponentDescriptor and emitting our own JavaScript component $create statement Listing 724 shows how we can alter our ErrorHandler server control to control the disposal of the component
Encode UCC - 12 In VS .NET
Using Barcode generator for VS .NET Control to generate, create UCC - 12 image in Visual Studio .NET applications.
Listing 724 Updating ErrorHandler to Manually Create the ErrorHandler Component
Barcode Reader In Java
Using Barcode recognizer for Java Control to read, scan read, scan image in Java applications.
protected override IEnumerable<ScriptDescriptor> GetScriptDescriptors() { return null; } protected override void OnPreRender(EventArgs e) { baseOnPreRender(e); string createErrorHandler = @" SysApplicationadd_init( function() { var errHandler = $find('ErrorHandler'); if (errHandler === null) { $create(ErrorHandler, {id:'ErrorHandler'}, null, null, null); } } );"; ScriptManagerRegisterStartupScript( this,
Generating GS1 128 In Java
Using Barcode creation for Java Control to generate, create UCC - 12 image in Java applications.
Loading of JavaScript Statements and File s
Bar Code Drawer In Java
Using Barcode generator for Java Control to generate, create bar code image in Java applications.
typeof(ErrorHandler), "ErrorHandlerCreate", createErrorHandler, true); }
Code 128 Code Set A Creation In Visual Basic .NET
Using Barcode maker for .NET framework Control to generate, create Code 128 Code Set C image in .NET framework applications.
The rst thing we do in the server control is not use a ScriptComponent
Descriptor to create the ErrorHandler component Instead, we use the OnPreRender method to register a startup script that will create the ErrorHandler if it does not already exist
Now, our component will be disposed of only when the page unloads, and it will be created only if it doesn t already exist We can cause partial postbacks as many times as we want and our component will not be disposed of and re-created
Loading of JavaScript Statements and Files
The way the UpdatePanel processes your scripts as they are returned from a partial page rendering can be a bit confusing at rst In many cases, some of the techniques you have used in the past for registering scripts no longer function correctly during a partial postback, and worse yet, some script registration techniques will work during the page s initial request and during a postback but will not work during a partial postback The goal of this section is to understand why this is happening and how to adjust your coding approach to have a consistent client script registration experience during all these cases
ScriptManager Registration Methods The ClientScriptManager s static RegisterXXX methods that we access through the page s ClientScript property have been the preferred way of registering scripts since the release of ASPNET 20 However, with the new partial postback capabilities provided by ASPNET AJAX, the ClientScriptManager and its RegisterXXX methods no longer work across all page-rendering situations Speci cally, the ClientScriptManager s RegisterXXX methods do not work properly during a partial postback This is the case because the UpdatePanel, ScriptManager, and a private object of type PageRequestManager take over responsibility for generating