WPF - Updating DependencyProperty Metadata

What is the technica开发者_Go百科l reason for not being able to update a DependencyProperty's metadata after it has already been set?

If you try to do something similar to below it will generate an exception saying:

Cannot change property metadata after it has been associated with a property.

MyProperty.DefaultMetata.PropertyChangedCallback = 
    new PropertyChangedCallback(MyMethod);

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Immutable objects have many benefits, one of which is thread-safety.

Also, metadata exists on a per-type basis; setting PropertyChangedCallback directly would effectively erase all other callbacks in the inheritance hierarchy.

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Does this question from Stackoverflow help any. WPF Property Callback

If that doesn't help. What do you mean by set, set in vs2k8 dev or set in the dll.