ListBox PROBLEM in User control

Discussion in 'ASP .Net Building Controls' started by Pierre, Mar 4, 2005.

  1. Pierre

    Pierre Guest


    I'm trying to develop a simple Web User Control that contains two list
    boxes, Add and Remove buttons. This User Control transfers the selected
    items from left list box to right list box and vice-versa, depending on the
    button clicked. The SelectionMode of both list boxes is "Multiple" and
    AutoPostBack is set to false.

    Here is the simple process:
    string strItemsToKeep = "";
    // Collect all items selected from lbLeftList list box.
    foreach( ListItem item in lbLeftList.Items )
    if( item.Selected )
    lbRightList.Items.Add( item.Text );
    strItemsToKeep = strItemsToKeep + item.Text + ";";
    Then after the loop, I process the string and load it back to the left list
    box. This works great within a simple aspx page.

    But, here's my problem:
    In a User Control ascx page, in the Code Behind, for each item retrieved
    from lbLeftList, I can see the data in each item.Text but the item.Selected
    is always false.

    After searching on the Web, I tried the following:
    System.Web.UI.UserControl UserControl;
    UserControl =
    //which is the name of the User Control in the parent page.

    System.Web.UI.WebControls.ListBox lb;
    lb = (System.Web.UI.WebControls.ListBox)UserControl.FindControl("lbLeftList");

    I thought that I could finally retrieve the correct information but, once
    again, I have the same problem: the lb.Items[0].Selected (which is the one I
    selected) is also set to false.

    I really do not understand what is going on. If somebody can help me it
    will greatly be appreciated.

    Thank you very much.
    Pierre, Mar 4, 2005
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  2. Pierre

    recoil Guest

    Several things.
    your user control should be implementing INamingContainer. Append it to
    your class definition as such
    public class MyUserControl : WebControl, INamingContainer

    Then make sure that the control is created around the OnInit event. If
    need be You can override OnInit and create all of your control's in
    Then Set the ID's of the control.
    then call base.OnInit();

    If you follow those 3 steps almosdt ALL of your problems should
    Then just remember that you should not try accessing the varaibles
    until AFTER the LoadViewState has been called which means that you can
    either Overload LoadViewState and call base.LoadViewstate and then
    perform your actions there or you can override OnLoad and stick your
    logic code there.
    recoil, Mar 5, 2005
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