operations on list boxes

I have implemented an asp.net listbox in my project. The listbox includes two buttons, one for adding items and the other for removing them. I have used a JavaScript function to handle item removal from the listbox. However, when I add new items after removing some, the previously removed items reappear in the list.

<asp:ListBox ID="sLstbox" runat="server" Width="250px" Height="150px" TabIndex="10"></asp:ListBox>

<asp:LinkButton ID="sLbtnAdd" runat="server" ></asp:LinkButton>&nbsp; 
<a href="#" id="hAncRemove" runat="server" onclick="fncRemoveItems();">Remove</a>    

function fncRemoveItems()
{
    var i;
    var strIDs="";
    var items = document.getElementById("sLstbox");
    alert(items.options.length);
    for (i = items.options.length - 1; i >= 0; i--)
    {
        if (items.options[i].selected)
            items.remove(i);
    }
}

IN code

Protected Sub sLbtnAdd_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles sLbtnAdd.Click

    Dim li As New ListItem
    li.Value = "1"
    li.Text = "test"
    sLstbox.Items.Add(li)
End Sub

Answer №1

For this situation, it is recommended to utilize standard < select > boxes. asp:listboxes are designed for server-side manipulation and may require extra steps to customize according to your preferences.

By using regular select-boxes (whether runat server or not), the process should be much simpler.

Answer №2

To simplify your life and achieve the 'AJAX' effect, consider placing everything inside an UpdatePanel and handling it server side. Manipulating an asp:ListBox with JavaScript can be quite cumbersome.

Below is a functional example demonstrating the aspx code and the corresponding codebehind implementation for your specific scenario:

<asp:UpdatePanel ID="yourUpdatePanel" runat="server">
    <ContentTemplate>
        <asp:ListBox ID="sLstbox" runat="server" Width="250px" Height="150px" TabIndex="10"></asp:ListBox> 
        <asp:LinkButton ID="sLbtnAdd" runat="server" OnClick="sLbtnAdd_Click" ></asp:LinkButton>&nbsp;  
        <asp:LinkButton ID="sLbtnRemove" runat="server"  OnClick="sLbtnRemove_Click"></asp:LinkButton>&nbsp;        
    </ContentTemplate>
</asp:UpdatePanel>    

In the codebehind file:

Protected Sub sLbtnAdd_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles sLbtnAdd.Click            
    Dim li As New ListItem      
    li.Value = "1"      
    li.Text = "test"      
    sLstbox.Items.Add(li)      
End Sub 

Protected Sub sLbtnRemove_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles sLbtnAdd.Click            
    For i As Integer = sLstbox.Items.Count - 1 To 0 Step -1
        If sLstbox.Items(i).Selected Then
            sLstbox.Items.Remove(sLstbox.Items(i))
        End If
    Next
End Sub 

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