UserForms- TcxListBox Question

I did not see a method for it, and this is kind of sloppy looking by the way the control draws, but it is one way of handling it.

Where List_XLS would be your userform, and lstXLS would be your TcxListBox, and chkAll would be your checkbox with the OnClick handler of function "checkedall":

function checkedall(sender) {
    /*
      make sure multiselect is enabled
    */
    UserForms.List_XLS.lstXLS.MultiSelect = true;
    
    /*
      if checked then set selected of each item in the listbox
    */
    if (UserForms.List_XLS.chkAll.Checked){
      for (var c = 0; c < UserForms.List_XLS.lstXLS.Items.Count;c++) {
        UserForms.List_XLS.lstXLS.Selected(c) = true;
      }
    }
    
    /*
      if checked then remove selected of each item in the listbox
    */
    if (!UserForms.List_XLS.chkAll.Checked) {
      for (var c = 0; c < UserForms.List_XLS.lstXLS.Items.Count;c++) {
        UserForms.List_XLS.lstXLS.Selected(c) = false;
      }
    }
}