WPF Trigger based on Object Type

Exist picture Exist · Oct 30, 2009 · Viewed 25.7k times · Source

Is there a way to do a comparison on object type for a trigger?

<DataTrigger Binding="{Binding SelectedItem}" Value="SelectedItem's Type">
</DataTrigger>

Background: I have a Toolbar and I want to Hide button's depending on what subclass is currently set to the selected item object.

Thanks

Answer

Greg Sansom picture Greg Sansom · Feb 11, 2011

This is based on @AndyG's answer but is a bit safer because it's strongly typed.

Implement an IValueConverter named DataTypeConverter, which accepts an object and returns its Type (as a System.Type):

public class DataTypeConverter:IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, 
      CultureInfo culture)
    {
        return value?.GetType() ?? Binding.DoNothing;
    }

    public object ConvertBack(object value, Type targetType, object parameter,
      CultureInfo culture)
    {
       throw new NotImplementedException();
    }
}

Change your DataTrigger to use the Converter, and set the value to the Type:

<DataTrigger Binding="{Binding SelectedItem,  
      Converter={StaticResource DataTypeConverter}}" 
      Value="{x:Type local:MyType}">
...
</DataTrigger>

Declare DataTypeConverter in the resources:

<UserControl.Resources>
    <v:DataTypeConverter x:Key="DataTypeConverter"></v:DataTypeConverter>
</UserControl.Resources>