#1,154 – Providing Default Values for Standard Dependency Properties in Custom Controls

September 9, 2014 1 Comment

When you define a custom control, you may define some custom dependency properties. For each property that you define, you specify metadata for your new dependency property, including default values.

You may also want to specify default values for dependency properties used by your class, but defined elsewhere.  In the code fragment below, we’re defining a custom shape that inherits from the Shape class.  We don’t want the user to have to provide values for the Stroke and Fill properties, so we use the OverrideMetadata method to provide default values.  Note that the user can still provide their own values for these properties.

    public class PieSlice : Shape
    {
        static PieSlice()
        {
            Brush myGreenBrush = new SolidColorBrush(Color.FromArgb(255, 6, 176, 37));
            myGreenBrush.Freeze();

            StrokeProperty.OverrideMetadata(
                typeof(PieSlice),
                new FrameworkPropertyMetadata(myGreenBrush));
            FillProperty.OverrideMetadata(
                typeof(PieSlice),
                new FrameworkPropertyMetadata(myGreenBrush));
        }

        // Remainder of custom control here..
    }

Filed under Graphics Tagged with , , ,

#163 – Constructing FrameworkPropertyMetadata

December 22, 2010 Leave a comment

When you look at the metadata for a dependency property that is storing its metadata as an instance of FrameworkPropertyMetadata, you’ll see a series of boolean properties.

As a convenience, when constructing an instance of FrameworkPropertyMetadata, you don’t have to pass all of these boolean values into the constructor individually.  Instead, the constructor accepts a flags parameter that is a logical OR of a series of enumeration values.  The individual enumeration values come from the FrameworkPropertyMetadataOptions enum.

        // Register ZHeightProperty dependency property
        private static FrameworkPropertyMetadata meta = new FrameworkPropertyMetadata(1,   // default = 1
            FrameworkPropertyMetadataOptions.AffectsArrange | FrameworkPropertyMetadataOptions.AffectsMeasure |
            FrameworkPropertyMetadataOptions.AffectsParentArrange | FrameworkPropertyMetadataOptions.AffectsParentMeasure |
            FrameworkPropertyMetadataOptions.BindsTwoWayByDefault);

        public static readonly DependencyProperty ZHeightProperty =
            DependencyProperty.Register("ZHeightProperty", typeof(int), typeof(ThreeDButton), meta);

Filed under Dependency Properties Tagged with , , ,

#161 – Read a Dependency Property’s Metadata

December 20, 2010 Leave a comment

You can read a dependency property’s metadata by using the DependencyProperty.GetMetadata method.

For example, assume that we have a Dog class with a BirthYear dependency property and that the class has exposed BirthYearProperty as a public member.  We can retrieve the property’s metadata as follows:

            Dog fido = new Dog("Fido");
            PropertyMetadata meta = Dog.BirthYearProperty.GetMetadata(fido);

Filed under Dependency Properties Tagged with , ,

#89 – Using Visual Studio to Follow the Inheritance Chain for WPF Types

October 9, 2010 Leave a comment

The inheritance chain for WPF classes is pretty deep.  The Button class, for example, inherits from ButtonBase, and then from ContentControl, Control, FrameworkElement, etc.

You can look classes up in the MSDN documentation to find out which classes a particular class inherits from and which properties and methods it inherits.  Or you can use the Go To Definition feature in Visual Studio 2010 to follow the chain.

Assume you have some code that mentions the Button class.  You can right-click on the word “Button” and select Go To Definition.

You’ll see the metadata for Button and that it inherits from ButtonBase.

To follow the chain, right-click on ButtonBase and select Go To Definition again.

Again, a metadata window comes up, this time showing you the metadata for the ButtonBase class–and the fact that ButtonBase inherits from ContentControl.

The containing DLL is also listed at the top of the window.

Filed under Visual Studio Tagged with , ,