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POHow to add callbacks to Framework Element's Visibility Dependency Property?
 

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  1. POHow to add callbacks to Framework Element's Visibility Dependency Property?
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    <p>I'm using a dependency property which handles the fade-in / fade-out of a Framework Element. </p> <p>The property is able to handle the fade-in / fade-out animation by registering callback methods for whenever the Visibility property of the animated element has changed.</p> <p>This was done by the previous coder as such:</p> <pre><code>UIElement.VisibilityProperty.AddOwner(typeof (FrameworkElement), new FrameworkPropertyMetadata(Visibility.Visible, VisibilityChanged, CoerceVisibility)); </code></pre> <p>The problem here is that FrameworkElement is already an owner of the VisibilityProperty, and as such triggers an exception which was catched (luckily) by ExpressionBlend.</p> <p>To counter this problem, I noticed that Dependency Properties have a "OverwriteMetadata" method, which allows someone to overwrite the metadata of a given type, in my case FrameworkElement.</p> <p>As such, I could use the following instead:</p> <pre><code>UIElement.VisibilityProperty.OverrideMetadata(typeof(FrameworkElement), new FrameworkPropertyMetadata(Visibility.Visible, VisibilityChanged, CoerceVisibility)); </code></pre> <p>My question is: </p> <p>How safe is it to overwrite FrameworkElement's Visibility's metadata ? If its unsafe, what other alternatives do I have ?</p> <p>EDIT: Well, scratch that... Apparently overwriting the metadata triggers another exception: "PropertyMetadata is already registered for type 'FrameworkElement'. </p> <p>How can I add the callback methods for the dependency property, if I'm unable to add an owner or overwrite the metadata ? </p> <p>Am I forced to create a class which derives from FrameworkElement, add it as an owner of the VisibilityProperty, and make all controls who use that property be of the same type as the derived class ?</p>
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    1. USHussein Khalil
    1. USHussein Khalil
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      1. POHow to add callbacks to Framework Element's Visibility Dependency Property?
      1. USErik Öjebo
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