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

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7: Control Development in a Partial Postback Environment
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same $create statement it did on the initial page load Figure 77 shows the response received after clicking the Update button The highlighted portion shows the $create statement that was emitted by the ScriptComponent Descriptor
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Figure 77 Re-creating Comp 1 during a partial postback
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Whereas a client component is re-created in a partial postback when its containing server control is re-rendered and the control s Script Descriptors are processed, how a client component is automatically disposed differs depending on whether the component is truly a component, directly inheriting from SysComponent, or whether it is a control or behavior Because the disposal methods differ and because knowing how and when your client component is disposed allows you to correct disposing problems and tweak the disposal pattern, let s take a closer look at them First, we focus on how controls and behaviors are automatically disposed, and then we focus on how components are automatically disposed
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The Effe cts of a Partial Postback on Client Components
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Automatic Disposal of Behaviors and Controls Automatic disposal of a behavior or control occurs during a partial postback when the behavior s or control s associated DOM element is destroyed DOM elements are destroyed when they are contained within a section of the DOM tree that is being replaced by a partial postback response To illustrate this, we place an ASPNET AJAX server control that creates a client behavior inside an UpdatePanel and then cause the UpdatePanel to update Listing 75, Listing 76, and Listing 77 highlight the code for our Simple Behavior test page and control
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Listing 75 SimpleBehaviorjs
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SimpleBehavior = function(element) { SimpleBehaviorinitializeBase(this, [element]); }; SimpleBehaviorprototype = { dispose: function() { SysDebugtrace (Stringformat("Behavior: {0} disposed", thisget_id())); SimpleBehaviorcallBaseMethod(this, 'dispose'); } }; SimpleBehaviorregisterClass("SimpleBehavior", SysUIBehavior);
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Listing 76 SimpleBehaviorcs
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using SystemWebUI; using SystemCollectionsGeneric; [assembly: WebResource ("ControlsJavaScriptSimpleBehaviorjs", "text/javascript")] namespace Controls { public class SimpleBehavior : ScriptControl { protected override IEnumerable<ScriptDescriptor> GetScriptDescriptors() { yield return new ScriptBehaviorDescriptor("SimpleBehavior", thisClientID); }
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7: Control Development in a Partial Postback Environment
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Listing 76 continued
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protected override IEnumerable<ScriptReference> GetScriptReferences() { yield return new ScriptReference( "ControlsJavaScriptSimpleBehaviorjs", "Controls"); } } }
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Listing 77 SimpleBehavioraspx
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<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="SimpleBehavioraspxcs" Inherits="_7SimpleBehavior" %> <%@ Register Assembly="Controls" Namespace="Controls" TagPrefix="cc1" %> <html> <head runat="server"> <title>Simple Behavior</title> </head> <body> <form id="form1" runat="server"> <asp:ScriptManager ID="SM1" runat="server" /> <asp:UpdatePanel ID="UP1" runat="server" UpdateMode="Conditional"> <ContentTemplate> <cc1:SimpleBehavior ID="Beh1" runat="server" /> <asp:Button ID="tstButton" Text="Update" runat="server" /> </ContentTemplate> </asp:UpdatePanel> </form> </body> </html>
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Looking at Listing 78, which partially shows the HTML created when the Simple Behavior page is rst rendered, we can see that the UpdatePanel, represented by the div tag with id="UP1", contains the span tag that represents the Beh1 instance of the SimpleBehavior server control There is also
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The Effe cts of a Partial Postback on Client Components
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a SimpleBehavior behavior attached to that span tag by the highlighted $create statement
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Listing 78 Rendered HTML from SimpleBehavioraspx
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<html xmlns="http://wwww3org/1999/xhtml" > <head> <title> Simple Behavior </title> </head> <body> <form name="form1" method="post" action="SimpleBehavioraspx" id="form1"> <div id="UP1"> <span id="Beh1"></span> <input type="submit" name="tstButton" value="Update" id="tstButton" /> </div> <script type="text/javascript"> //<![CDATA[ SysApplicationinitialize(); SysApplicationadd_init(function() { $create(SimpleBehavior, null, null, null, $get("Beh1")); }); //]]> </script> </form> </body> </html>
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When we click the Update button, UpdatePanel UP1 s content, which includes the span tag created for the Beh1 SimpleBehavior, is going to be replaced with new content We can see this by using Web Development Helper to capture the HTTP traf c Figure 78 shows the captured response and highlights the portion that indicates that UP1 s content will be replaced
7: Control Development in a Partial Postback Environment
Figure 78 UpdatePanel UP1 s content being replaced
Right before UP1 s content is replaced with the new content, a method on the client PageRequestManager object called _destroyTree is executed _destroyTree s responsibility is to nd any behaviors or controls that are attached to any DOM element contained within UP1 s DOM tree and call dispose on it The method does this by recursively iterating through UP1 s DOM tree and determining whether there is a control or behaviors attached to the current DOM element It nds controls through the control expando property that will be attached to the DOM element if a control is attached, and it nds behaviors by using the static method SysUIBehaviorget Behaviors, which returns all behaviors attached to a given DOM element If it nds attached controls or attached behaviors, it calls dispose on each control or behavior and moves on This is how behaviors and controls are automatically disposed