asp.net - Value set using JavaScript is not persisted on Postback - Stack Overflow

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I have two list controls in my asp page and am populating the second list control using javascript. Problem is the script executes and i can see the value moved from first list box (ConfiguredOrgListBox) to second list box(SelectedOrgListBox) but when i try to save using submit button i find my second list as empty and first list box as it was earlier. Below is the script and mark up.

    //call this method to register the script    
    private void CreateMoveOrganizationScript(StringBuilder sb) {
        sb.Append( @"<script language=javascript type=text/javascript>;
                    function moveOrganisation() {");            
        sb.Append( @"var source = document.getElementById('"+ ConfiguredOrgListBox.ClientID  +@"');
                    var target = document.getElementById('"+SelectedOrgListBox.ClientID+ @"');
                    if ((source != null) && (target != null)) {
                    var newOption = new Option();
                    newOption.text = source.options[source.options.selectedIndex].text;
                    newOption.value = source.options[source.options.selectedIndex].value;

                    target.options[target.length] = newOption;
                    source.remove(source.options.selectedIndex)  ;
                    }            
                } </script>");            
    }

Markup

      <asp:Label ID="ConfiguredOrgLabel" runat="server" Text="Available Organizations"></asp:Label><br />
      <asp:ListBox ID="ConfiguredOrgListBox" runat="server" Width="98%" Height="100px"></asp:ListBox>
       <input id="MoveOrgRight" type="button" value=">>" onclick="moveOrganisation()" />
      <asp:Label ID="SelectedOrgLabel" runat="server" Text="Selected VNA Organizations"></asp:Label><br />
      <asp:ListBox ID="SelectedOrgListBox" runat="server" Width="98%" Height="100px"></asp:ListBox>

Please let me know what I am doing wrong

Regards, JeeZ

I have two list controls in my asp page and am populating the second list control using javascript. Problem is the script executes and i can see the value moved from first list box (ConfiguredOrgListBox) to second list box(SelectedOrgListBox) but when i try to save using submit button i find my second list as empty and first list box as it was earlier. Below is the script and mark up.

    //call this method to register the script    
    private void CreateMoveOrganizationScript(StringBuilder sb) {
        sb.Append( @"<script language=javascript type=text/javascript>;
                    function moveOrganisation() {");            
        sb.Append( @"var source = document.getElementById('"+ ConfiguredOrgListBox.ClientID  +@"');
                    var target = document.getElementById('"+SelectedOrgListBox.ClientID+ @"');
                    if ((source != null) && (target != null)) {
                    var newOption = new Option();
                    newOption.text = source.options[source.options.selectedIndex].text;
                    newOption.value = source.options[source.options.selectedIndex].value;

                    target.options[target.length] = newOption;
                    source.remove(source.options.selectedIndex)  ;
                    }            
                } </script>");            
    }

Markup

      <asp:Label ID="ConfiguredOrgLabel" runat="server" Text="Available Organizations"></asp:Label><br />
      <asp:ListBox ID="ConfiguredOrgListBox" runat="server" Width="98%" Height="100px"></asp:ListBox>
       <input id="MoveOrgRight" type="button" value=">>" onclick="moveOrganisation()" />
      <asp:Label ID="SelectedOrgLabel" runat="server" Text="Selected VNA Organizations"></asp:Label><br />
      <asp:ListBox ID="SelectedOrgListBox" runat="server" Width="98%" Height="100px"></asp:ListBox>

Please let me know what I am doing wrong

Regards, JeeZ

• javascript
• asp
• postback

Share Improve this question Follow edited Nov 3, 2010 at 21:59 palswim 12.2k88 gold badges5656 silver badges7979 bronze badges asked Nov 3, 2010 at 16:47 JeevanJeevan 8,7721414 gold badges5151 silver badges6969 bronze badges

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2 Answers 2

Sorted by: Reset to default 4

According to this, it's because the list box doesn't post back to tell the back-end that it's changed. They use a hidden field which holds info on what changes were made with JavaScript and then on postback it updates the back-end.

You need to process these changes during postback. When postback happens ASP.NET engine loads control's data from view state and it doesn't know that client modified values using javascript, so you should manually extract those values from Request.

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