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[Solved] $find... not working after ajax postback

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ComboBox

This is a migrated thread and some comments may be shown as answers.

Ken Lester asked on 02 Oct 2009, 03:25 AM

I have 2 ComboBox(cboA,cboB) and 1 Textbox in a Page.

When the cboA _SelectedIndexChanged (Server Side, AJax Postback), it will base on some condition to enable or disable cboB.

If cboB enabled and when cboB_OnClientSelectedIndexChanged(Client Side), it will call JS Script to Show or Hide the textbox.

Here is the JS script:

                             
                    function ShowHideTextbox() {         
                        var cboB = $find("<%= cboB.ClientID %>");         
                        var txtbox = $find("<%= textbox1.ClientID %>");         
                     
                        var SelectedText = cboB.get_text();         
                     
                        if (SelectedText == 'Other') {         
                            txtbox.set_visible(true);         
                        }         
                        else {         
                            txtbox.set_visible(false);         
                        }         
                    }         

Every time I will get the following error when the above script reach on this line var SelectedText = cboB.get_text();

"Microsoft JScript runtime error: 'null' is null or not an object".

3 Answers, 1 is accepted

answered on 02 Oct 2009, 06:19 PM

Hope some1 can help, here's i include the test code:

note: just try to select the item from 1st combobox and 2nd combobox randomly, after few times the textbox will no longer be able to show.

Markup:

                    <html xmlns="http://www.w3.org/1999/xhtml" >         
            <head runat="server">         
                <title></title>         
                          
            </head>         
            <script type="text/javascript">         
                function ChangeTextbox() {         
                    var cbo = $find("<%= RadComboBox2.ClientID %>");         
                    var txt = $find("<%= RadTextBox1.ClientID %>");         
                     
                    var SelectedText = cbo.get_text();         
                     
                    if (SelectedText == 'Other') {         
                        txt.set_visible(true);         
                    }         
                    else {         
                        txt.set_visible(false);         
                    }         
                }         
                </script>         
            <body>         
                     
                <form id="form1" runat="server">         
                <telerik:RadScriptManager ID="RadScriptManager1" runat="server">         
                </telerik:RadScriptManager>         
                  <telerik:RadAjaxManager ID="RadAjaxManager1" runat="server">         
                      <AjaxSettings>         
                          <telerik:AjaxSetting AjaxControlID="RadComboBox1">         
                              <UpdatedControls>         
                                  <telerik:AjaxUpdatedControl ControlID="RadComboBox2"          
                                      LoadingPanelID="RadAjaxLoadingPanel1" />         
                              </UpdatedControls>         
                          </telerik:AjaxSetting>         
                      </AjaxSettings>         
                    </telerik:RadAjaxManager>         
                <div>         
                         
                    <telerik:RadComboBox ID="RadComboBox1" Runat="server" AutoPostBack="True">         
                        <Items>         
                            <telerik:RadComboBoxItem runat="server" Text="RadComboBoxItem1"          
                                Value="RadComboBoxItem1" />         
                            <telerik:RadComboBoxItem runat="server" Text="RadComboBoxItem2"          
                                Value="RadComboBoxItem2" />         
                        </Items>         
                    </telerik:RadComboBox>         
                    <telerik:RadComboBox ID="RadComboBox2" Runat="server" OnClientSelectedIndexChanged=" ChangeTextbox">         
                        <Items>         
                            <telerik:RadComboBoxItem runat="server" Text="RadComboBoxItem1"          
                                Value="RadComboBoxItem1" />         
                            <telerik:RadComboBoxItem runat="server" Text="RadComboBoxItem2"          
                                Value="RadComboBoxItem2" />         
                            <telerik:RadComboBoxItem runat="server" Text="Other" Value="Other" />         
                        </Items>         
                    </telerik:RadComboBox>         
                    <telerik:RadTextBox ID="RadTextBox1" Runat="server">         
                    </telerik:RadTextBox>         
                           
                         
                </div>         
                  <telerik:RadAjaxLoadingPanel ID="RadAjaxLoadingPanel1" Runat="server"          
                      Skin="Default">         
                  </telerik:RadAjaxLoadingPanel>         
                </form>         
            </body>         
            </html>         

Code behind:

                      Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load         
                     
                End Sub         
                     
                Protected Sub RadComboBox1_SelectedIndexChanged(ByVal o As Object, ByVal e As Telerik.Web.UI.RadComboBoxSelectedIndexChangedEventArgs) Handles RadComboBox1.SelectedIndexChanged         
                    Select Case RadComboBox1.SelectedIndex         
                        Case 0         
                            RadComboBox2.Enabled = True         
                        Case 1         
                            RadComboBox2.Enabled = False         
                    End Select         
                End Sub         