#575 – PropertyMetadata vs. FrameworkPropertyMetadata

June 7, 2012 1 Comment

When you implement a custom dependency property and you register the property by calling DependencyProperty.Register, you specify some metadata for the property by passing it an instance of PropertyMetadata.  This can be an instance of the PropertyMetadata class or an instance of one of its subclasses.  The differences are shown below.

PropertyMetadata – Basic metadata relating to dependency properties

  • CoerceValueCallback – coerce the value when being set
  • DefaultValue – a default value for the property
  • PropertyChangedCallback – respond to new effective value for the property

UIPropertyMetadata – derives from PropertyMetadata and adds:

  • IsAnimationProhibited – disable animations for this property?

FrameworkPropertyMetadata – derives from UIPropertyMetadata and adds:

  • AffectsArrange, AffectsMeasure, AffectsParentArrange, AffectsParentMeasure, AffectsRender – Should layout calculations be re-run after property value changes?
  • BindsTwoWayByDefault, DefaultUpdateSourceTrigger, IsDataBindingAllowed, IsNotDataBindable – Dictates how property participates in data binding
  • Inherits, OverridesInheritanceBehavior – Does inheritance work for this property?
  • Journal – Store this value when journaling?
  • SubPropertiesDoNotAffectRender – Check properties of this object when layout changes?

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#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);

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#162 – UIPropertyMetadata and FrameworkPropertyMetadata

December 21, 2010 Leave a comment

Some dependency properties in WPF have metadata deriving from UIPropertyMetadata or FrameworkPropertyMetadata, rather than from PropertyMetadata.

For example, the ComboBox.IsEnabledProperty, which is defined in UIElement has metadata of type UIPropertyMetadata.

            UIPropertyMetadata meta = (UIPropertyMetadata)ComboBox.IsEnabledProperty.GetMetadata(cboTest);

UIPropertyMetadata derives from PropertyMetadata and adds the IsAnimationProhibited property.

The Button.IsEnabledProperty has metadata of type FrameworkPropertyMetadata.

            FrameworkPropertyMetadata meta = (FrameworkPropertyMetadata)Button.IsEnabledProperty.GetMetadata(btnTest);

FrameworkPropertyMetadata derives from UIPropertyMetadata and adds properties related to layout.

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