When I move through a list box, why do my checked items become unchecked?

Question

The code below moves the selected item in the listbox downwards to the next item in the listbox, but it unchecks the selected item if it was checked. How can I prevent this?

private void buttonMoveDown_Click(object sender, EventArgs e)
{
   int iIndex = checkedListBox1.SelectedIndex;
   if (iIndex == -1)
   {
      return;
   }
   moveListboxItem(checkedListBox1,  iIndex, iIndex + 1);
}

Thanks

The code for moveListboxItem is as follows:

 private void moveListboxItem(CheckedListBox ctl, int fromIndex,int toIndex)
        {
            if(fromIndex == toIndex)
            {
                return;
            }
            if(fromIndex < 0 )
            {
                fromIndex = ctl.SelectedIndex;
            }
            if(toIndex < 0 || toIndex > ctl.Items.Count - 1)
            {
                return;
            }

            object data = ctl.Items[fromIndex];
            ctl.Items.RemoveAt(fromIndex);
            ctl.Items.Insert(toIndex, data);
            ctl.SelectedIndex = toIndex;
}

Answer 1

You'll need to post the code for moveListBoxItem in order for us to be able to help out.

My suspicion is that moveListBoxItem looks something like this.

void moveListBoxItem(CheckedListBox list, int oldIndex, int newIndex ) {
  object old = list.Items[oldIndex];
  list.Items.RemoveAt(oldIndex);
  list.Items.Insert(newIndex, old);
}

If that's the case, the reason it's not working is because once you remove the object, the CheckedListBox no longer tracks the checked state of the particular index. You'll need to re-add this later.

void moveListBoxItem(CheckedListBox list, int oldIndex, int newIndex ) {
  var state = list.GetItemCheckedState(oldIndex);
  object old = list.Items[oldIndex];
  list.Items.RemoveAt(oldIndex);
  list.Items.Insert(newIndex, old);
  list.SetItemCheckedState(newIndex, state);
}

EDIT: Update for the actual moveListBoxItem code. You need to propagate the CheckState to the new index as well. Removing it from the collection essentially clears the stored state.

private void moveListboxItem(CheckedListBox ctl, int fromIndex,int toIndex)
        {
            if(fromIndex == toIndex)
            {
                return;
            }
            if(fromIndex < 0 )
            {
                fromIndex = ctl.SelectedIndex;
            }
            if(toIndex < 0 || toIndex > ctl.Items.Count - 1)
            {
                return;
            }

            object data = ctl.Items[fromIndex];
            CheckState state = ctl.GetItemCheckState(fromIndex);
            ctl.Items.RemoveAt(fromIndex);
            ctl.Items.Insert(toIndex, data);
            ctl.SetItemCheckState(toIndex, state);
            ctl.SelectedIndex = toIndex;
}