Simple WPF IValueConverter and DataTrigger not working together

Question

I've been having trouble using a value converter with a data trigger. In some of my code it seems like the DataTrigger's Path is being applied to the root element, rather than the element which the style applies to.

I created a simple test case, and I don't understand its behavior. I'm expecting the Button to turn red or blue depending on which value is being fed to the DataTrigger's converter, but the Button isn't being affected at all!

<UserControl
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:SimpleWpfApplication"
    x:Class="SimpleWpfApplication.SimpleUserControl"
    ToolTip="UserControl ToolTip">
    <UserControl.Resources>
        <local:SimpleConverter x:Key="SimpleConverter" />
    </UserControl.Resources>
    <Button ToolTip="Button ToolTip">
        <Button.Style>
            <Style TargetType="{x:Type Button}">
                <Style.Triggers>
                    <DataTrigger
                        Binding="{Binding Path=ToolTip, Converter={StaticResource SimpleConverter}}"
                        Value="Button ToolTip">
                        <Setter Property="Background" Value="Red" />
                    </DataTrigger>
                    <DataTrigger
                        Binding="{Binding Path=ToolTip, Converter={StaticResource SimpleConverter}}"
                        Value="UserControl ToolTip">
                        <Setter Property="Background" Value="Blue" />
                    </DataTrigger>
                </Style.Triggers>
            </Style>
        </Button.Style>
    </Button>
</UserControl>

And a simple converter:

class SimpleConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return value;
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        throw new InvalidOperationException("SimpleConverter is a OneWay converter.");
    }
}

Why isn't Convert being called? Why doesn't the Button turn red or blue?

Answer 1

Found the answer in another StackOverflow question: What’s wrong with my datatrigger binding?

The answer is to add RelativeSource={RelativeSource Self} to the binding:

<DataTrigger Binding="{Binding Path=ToolTip,
                       RelativeSource={RelativeSource Self},
                       Converter={StaticResource SimpleConverter}}" />