#164 – Overriding Metadata for an Inherited Dependency Property

When deriving a new child class, you’ll the parent’s dependency properties.  You might also want to change the behavior of one or more of the dependency properties.  You can do this to some extent by overriding the metadata for a dependency property.

Overriding the metadata in the child class doesn’t change the behavior of the dependency property in the parent class.

In the example below, we create a new class and override metadata for several properties, changing the default values.

    public class ThermometerSlider : Slider
    {
        static ThermometerSlider()
        {
            // Defaults for standard Slider: Min = 0, Max = 10, Value = 0
            // Defaults for ThermometerSlider: Min = -40, Max = 120, Value = 70

            // Change default Minimum to -40.0
            MinimumProperty.OverrideMetadata(typeof(ThermometerSlider), new FrameworkPropertyMetadata(-40.0));

            // Change default Maximum to 120
            MaximumProperty.OverrideMetadata(typeof(ThermometerSlider), new FrameworkPropertyMetadata(120.0));

            // Change default Value to 70
            ValueProperty.OverrideMetadata(typeof(ThermometerSlider), new FrameworkPropertyMetadata(70.0));
        }
    }

The metadata type must match the type in the original property (e.g. FrameworkPropertyMetadata, UIPropertyMetadata, or PropertyMetadata).