How can I prevent a ToggleButton from being Toggled without setting IsEnabled=False

Question

I have a list of ToggleButtons being used as the ItemTemplate in a ListBox similar to this answer using the MultiSelect mode of the Listbox. However I need to make sure at least one item is always selected.

I can get the proper behavior from the ListBox by just adding an item back into the ListBox's SelectedItems collection on the ListBox.SelectionChanged event but my ToggleButton still moves out of its toggled state so I think I need to stop it earlier in the process.

I would like to do it without setting IsEnabled="False" on the last button Selected because I'd prefer to stay with the Enabled visual style without having to redo my button templates. Any ideas?

Answer 1

You can override the OnToggle method to prevent toggling the state, by not calling the base implementation :

public class LockableToggleButton : ToggleButton
{
    protected override void OnToggle()
    {
        if (!LockToggle)
        {
            base.OnToggle();
        }
    }

    public bool LockToggle
    {
        get { return (bool)GetValue(LockToggleProperty); }
        set { SetValue(LockToggleProperty, value); }
    }

    // Using a DependencyProperty as the backing store for LockToggle.  This enables animation, styling, binding, etc...
    public static readonly DependencyProperty LockToggleProperty =
        DependencyProperty.Register("LockToggle", typeof(bool), typeof(LockableToggleButton), new UIPropertyMetadata(false));
}

Answer 2

This is hackey, but if you don't want custom code you could always use the property "IsHitTestVisible", when you don't want them to uncheck it, simply set IsHitTestVisible equal to false. However, they may be able to tab to the control and toggle it using the space bar.