Tuesday, May 13, 2014

#575 – PropertyMetadata vs. FrameworkPropertyMetadata

     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?