markupextension

Using MarkupExtension in a converter

This approach will give you the opportunity to use your converter in a one-liner in Xaml. It will also make it possible to work with properties in your converter.

Example of a converter that is using MarkupExtension :

public class BoolToVisibilityConverter : MarkupExtension, IValueConverter
    {
        public override object ProvideValue(IServiceProvider serviceProvider)
        {
            return this; 
        }

        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            //Checks both if the value is null or if the converter somehow gets used ahead of time
            if (value == null || value == DependencyProperty.UnsetValue)
            {
                return false;
            }
            
            //Could not parse incoming value
            if (!bool.TryParse(value.ToString(), out var parsedResult)) return false;
            
            if (parsedResult)
            {
                return !Inverted ? Visibility.Visible : Visibility.Collapsed;
            }
            else
            {
                return !Inverted ? Visibility.Collapsed : Visibility.Visible;
            }
        }

        public bool Inverted { get; set; }

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

Code explanation:

This is a fairly normal converter to use when you are creating a Xaml based app. The converter takes a boolean value as input and returns a Visibility value based on the boolean value. This converter is used in MainWindow.xaml in order for it to determine when it should show its <TextBlock>'s.

Now, how can I reference this converter without having to add it as a <Window.Resource>(MainWindow, line 15-17) with a x:Key.

The magic here is that the converter is inheriting from MarkupExtension. This class requires you to provide a value, which is the value that should be returned to the element that requires the markup extension. In this case, MainWindow.xaml line 34.

This also gives me the opportunity to set properties when using the converter. In this case I have set the Inverted property to make the converter invert the output.