Question

Here is my code:

public string Units
    {
        get { return (string)GetValue(UnitsProperty); }
        set { SetValue(UnitsToolTipVisibility, Visibility.Visible);
                SetValue(UnitsProperty, value); }
    }
    public static readonly DependencyProperty UnitsProperty = DependencyProperty.Register("Units", typeof(string), typeof(UserInputOutput));
    public static readonly DependencyProperty UnitsToolTipVisibility = DependencyProperty.Register("UnitsToolTipVisibility", typeof(Visibility), typeof(UserInputOutput), new UIPropertyMetadata(Visibility.Visible));

My goal:
When the Units variable is Set I want the tooltip for this instance of the UserControl to become visible.

I think I’m going about this the wrong way. I have many, many instances of a UserControl. When an instance has the Units string set the tooltip for that instance should be visible.

Answer 1

It would be easier to just use a trigger in your XAML. You can get rid of the UnitsToolTipVisibilityProperty completely then.

<ToolTip>
   <ToolTip.Resources>
      <Style TargetType="ToolTip">
         <Style.Triggers>
              <!-- hide tooltip when no unit set -->
              <DataTrigger Binding="{Binding Units}" Value="{x:Null}">
                  <Setter Property="Visibility" Value="Collapsed" />
              </DataTrigger>
          </Style.Triggers>
       </Style>
    </ToolTip.Resources?
</ToolTip>