Responding to GetProperty

I've created a custom implementation of GetProperty for my binding but now I'm getting errors when I go to use the channels. Why is the validation for these channels failing?

This is an implementation problem that I've talked about in the past. There is a requirement that the values queried from design time objects, such as bindings and binding elements, match the values queried from runtime objects, such as a channels. If the two don't agree on a property value, then you can experience problems ranging from an error creating the channel to mysterious failures sending and receiving messages.

This problem most commonly happens when you override an existing property value on the binding but forget to override the property in the same way on the channels. Use this picture illustrating GetProperty to follow the chain of property values.

However, this problem can also happen even when you're not overriding an existing value. If you write a GetProperty implementation but forget to delegate to the inner channel or binding element, then the chain of GetProperty calls terminates right there. Any further channels or binding elements do not get to contribute to GetProperty evaluations. This can easily cause a discrepancy between the design time and runtime values of a property despite the fact that you didn't explicitly modify that property. In most cases, this is a severe enough problem to fail very quickly. If you've written a GetProperty method and are suddenly seeing property value mismatches for properties that you didn't touch though, then make sure that your GetProperty method is delegating any unhandled properties to the right place.

Next time: Preventing Anonymous Access

Comments

• Anonymous
  March 22, 2007
  Last time, we left off the channel construction process at the end of the design stage. During the design