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POASP.NET Framework 4 client callback demo code complains about ListBox1
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  1. POASP.NET Framework 4 client callback demo code complains about ListBox1
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    copied!<p>From this set of ASP.NET demo code:</p> <p><a href="http://msdn.microsoft.com/en-us/library/ms178209.aspx" rel="nofollow">http://msdn.microsoft.com/en-us/library/ms178209.aspx</a></p> <p>in VS2010 in an ASP.NET project, I get error message: </p> <p>"The name 'ListBox1' does not exist in the current context" from the C# source file where the ListBox1 is referenced (lines 35-37). If I add a declaration for the ListBox1 within the class, the error goes away but when I press F5 to run it, I get a message that the ListBox1 has already been defined. What have I missed?</p> <p>ClientCallback.aspx.cs:</p> <pre><code>using System; using System.Data; using System.Configuration; using System.Collections; using System.Web; using System.Web.Security; using System.Web.UI; using System.Web.UI.WebControls; using System.Web.UI.WebControls.WebParts; using System.Web.UI.HtmlControls; public partial class ClientCallback : System.Web.UI.Page, System.Web.UI.ICallbackEventHandler { // protected ListBox ListBox1; protected System.Collections.Specialized.ListDictionary catalog; protected String returnValue; protected void Page_Load(object sender, EventArgs e) { String cbReference = Page.ClientScript.GetCallbackEventReference(this, "arg", "ReceiveServerData", "context"); String callbackScript; callbackScript = "function CallServer(arg, context)" + "{ " + cbReference + ";}"; Page.ClientScript.RegisterClientScriptBlock(this.GetType(), "CallServer", callbackScript, true); catalog = new System.Collections.Specialized.ListDictionary(); catalog.Add("monitor", 12); catalog.Add("laptop", 10); catalog.Add("keyboard", 23); catalog.Add("mouse", 17); ListBox1.DataSource = catalog; ListBox1.DataTextField = "key"; ListBox1.DataBind(); } public void RaiseCallbackEvent(String eventArgument) { if (catalog[eventArgument] == null) { returnValue = "-1"; } else { returnValue = catalog[eventArgument].ToString(); } } public String GetCallbackResult() { return returnValue; } } </code></pre> <p>and ClientCallback.aspx:</p> <pre><code>&lt;%@ Page Language="C#" AutoEventWireup="true" CodeFile="ClientCallback.aspx.cs" Inherits="ClientCallback" %&gt; &lt;!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd"&gt; &lt;html &gt; &lt;head id="Head1" runat="server"&gt; &lt;title&gt;Client Callback Example&lt;/title&gt; &lt;script type="text/ecmascript"&gt; function LookUpStock() { var lb = document.getElementById("&lt;%=ListBox1.ClientID%&gt;"); try { var product = lb.options[lb.selectedIndex].text; CallServer(product, ""); } catch (err) { alert("Please select a product."); } } function ReceiveServerData(rValue) { document.getElementById("&lt;%=ResultsSpan.ClientID%&gt;").innerHTML = rValue; } &lt;/script&gt; &lt;/head&gt; &lt;body&gt; &lt;form id="form1" runat="server"&gt; &lt;div&gt; &lt;asp:ListBox ID="ListBox1" Runat="server"&gt;&lt;/asp:ListBox&gt; &lt;br /&gt; &lt;br /&gt; &lt;input type="button" value="Look Up Stock" onclick="LookUpStock()" /&gt; &lt;br /&gt; &lt;br /&gt; Items in stock: &lt;span id="ResultsSpan" runat="server"&gt;&lt;/span&gt; &lt;br /&gt; &lt;/div&gt; &lt;/form&gt; &lt;/body&gt; &lt;/html&gt; </code></pre>
 

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