ASP.NET V2 and Client Callbacks


Callback.ASPX page to invoke the client callback

<%@ Page MasterPageFile="~/Site.master" Language="C#" CompileWith="Callback.aspx.cs" ClassName="Callback_aspx" Title="Client Callback Manager" %>
<%@ Implements Interface="System.Web.UI.ICallbackEventHandler" %>

<asp:Content ID="TitleContent" ContentPlaceHolderID="Title" Runat="server">
Client Callback Manager</asp:Content>

<asp:Content ID="DescriptionContent" ContentPlaceHolderID="Description" Runat="server">
This page demonstrates how to use ASP.NET's Client Callback Manager to perform lightweight callbacks to a Web server</asp:Content>

<asp:Content ID="MainContent" ContentPlaceHolderID="Main" Runat="server">
            <td style="width: 100px; height: 10px">
            <td style="width: 100px; height: 10px">
                <asp:TextBox ID="Name" Runat="server"></asp:TextBox>
            <td style="width: 100px; height: 10px">
            <td style="width: 100px">
            <td style="width: 100px">
                <asp:TextBox ID="Address" Runat="server"></asp:TextBox>
            <td style="width: 100px">
            <td style="width: 100px">
            <td style="width: 100px">
                <asp:TextBox ID="City" Runat="server"></asp:TextBox>
            <td style="width: 100px">
            <td style="width: 100px">
            <td style="width: 100px">
                <asp:DropDownList ID="State" Runat="server">
                    <asp:ListItem Text="AL" />
                    <asp:ListItem Text="AK" />
                    <asp:ListItem Text="VIC" />
                    <asp:ListItem Text="NS" />
                    <asp:ListItem Text="SA" />
                    <asp:ListItem Text="CO" />
                    <asp:ListItem Text="CT" />
                    <asp:ListItem Text="DC" />
                    <asp:ListItem Text="DE" />
                    <asp:ListItem Text="FL" />
                    <asp:ListItem Text="GA" />
                    <asp:ListItem Text="HI" />
                    <asp:ListItem Text="IA" />
                    <asp:ListItem Text="ID" />
                    <asp:ListItem Text="IL" />
                    <asp:ListItem Text="IN" />
                    <asp:ListItem Text="KS" />
                    <asp:ListItem Text="KY" />
                    <asp:ListItem Text="LA" />
                    <asp:ListItem Text="MA" />
                    <asp:ListItem Text="MD" />
                    <asp:ListItem Text="ME" />
                    <asp:ListItem Text="MI" />
                    <asp:ListItem Text="MN" />
                    <asp:ListItem Text="MO" />
                    <asp:ListItem Text="MS" />
                    <asp:ListItem Text="MT" />
                    <asp:ListItem Text="NC" />
                    <asp:ListItem Text="ND" />
                    <asp:ListItem Text="NE" />
                    <asp:ListItem Text="NH" />
                    <asp:ListItem Text="NJ" />
                    <asp:ListItem Text="NM" />
                    <asp:ListItem Text="NV" />
                    <asp:ListItem Text="NY" />
                    <asp:ListItem Text="OH" />
                    <asp:ListItem Text="OK" />
                    <asp:ListItem Text="OR" />
                    <asp:ListItem Text="PA" />
                    <asp:ListItem Text="RI" />
                    <asp:ListItem Text="SC" />
                    <asp:ListItem Text="SD" />
                    <asp:ListItem Text="TN" />
                    <asp:ListItem Text="TX" />
                    <asp:ListItem Text="UT" />
                    <asp:ListItem Text="VA" />
                    <asp:ListItem Text="VT" />
                    <asp:ListItem Text="WA" />
                    <asp:ListItem Text="WI" />
                    <asp:ListItem Text="WV" />
                    <asp:ListItem Text="WY" />
            <td style="width: 100px">
            <td style="width: 100px">
                Post Code</td>
            <td style="width: 100px">
                <asp:TextBox ID="Zip" Runat="server"></asp:TextBox>
            <td style="width: 100px">
                <asp:Button ID="AutofillButton" Runat="server" Text="Autofill" />

Callback.ASPX.CS file

public partial class Callback_aspx
 static readonly string _script =
  "<script language=\"javascript\">\n"                    +
  "function __onCallbackCompleted (result, context)\n"    +
  "{{\n"                                                  +
  "    var len = result.length;\n"                        +
  "    var city = result.substring (0, len - 3);\n"       +
  "    var state = result.substring (len - 2, len)\n"     +
  "    document.getElementById ('{0}').value = city;\n"   +
  "    var select = document.getElementById ('{1}');\n"   +
  "    for (var i=0; i<select.options.length; i++) {{\n"  +
  "        if (select.options[i].text == state) {{\n"     +
  "            select.options[i].selected = true;\n"      +
  "            break;\n"                                  +
  "        }}\n"                                          +
  "    }}\n"                                              +
  "}}\n"                                                  +

    void Page_Load (object sender, EventArgs e)
        // Get a callback event reference
        string cbref = GetCallbackEventReference (this,
            String.Format ("document.getElementById ('{0}').value", Zip.ClientID),
            "__onCallbackCompleted", "null", "null");

        // Wire the callback event reference to the Autofill button with
        // an onclick attribute, and add "return false" to event reference
        // to prevent a postback from occurring
        AutofillButton.Attributes.Add ("onclick", cbref + "; return false;");

  // Register a block of client-side script containing __onCallbackCompleted
  RegisterClientScriptBlock ("MyScript", String.Format (_script, City.ClientID,

    // Server-side callback event handler
    string ICallbackEventHandler.RaiseCallbackEvent(string arg)
  string state = arg.ToUpper();
  if (state.StartsWith("3187"))
   return "Brighton;VIC";
  else if (state.StartsWith("SA"))
   return "South Australia;SA";
  else if (state.StartsWith("NS"))
   return "New South Wales;NSW";
            return "Unknown;TK";

Comments (5)

  1. Dave Glover says:
  2. Sugandh says:

    Hi, dave

    I am trying to make a flicker free website using script callback in ASP.NET 1.1.

    I have a javascript function which is called when a button is clicked.

    request goes to the server and I render my user control and write it to the response stream.

    I have a span tag in which i am putting the render code of the data returned by my request.

    One problem that i am facing is, alignment.

    I have few text to which style should have been applied, but it is not doing, but it is doing when i post back data or the other text in the page.

    This is something that i am not able to figure out, any help or hint from you would be great for me.

    Thanks in advance.



  3. Sugandh says:

    hey sorry to bug you,

    solved the problem.



  4. Dave Glover says:

    Cool, PS have you looked at SmartNavigation? Cheers Dave

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