Question

I have to use functionality that is in another application domain. The result should be displayed in user control.

I have something like that:

var instance = domain.CreateInstanceFromAndUnwrap(...);
instance.Foo(myWpfUserControl as ICallback);

Foo(ICallback itf) {
   itf.SetData("...");
}

WpfUserControl.SetData(string data)
{
   if (!Dispatcher.CheckAccess())
     Dispatcher.Invoke(...)
   ...
}  

I had to put [Serializable] attribute onto WpfUserControll class and implement serialization contructor as well as ISerializable interface but now i receive exception:

The calling thread must be STA because many UI components require this 

that is raised from UserControl() constructor

What shall I do to avoid this ?
Thank you in advance !

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Solution

as @Al noticed, my user control have to be serialized when it comes to cross-application-domain calls. Now i pass proxy, that implements ICallback interface. Proxy was marked with Serializable attribute.

Proxy implementation should have absolutely no knowledge about user control as there should be an attempt to deserialize user control instance once again. When I tried to abstract proxy from user control via interface it didn’t help. When i tried to pass interface to proxy (that was implemented by user control) – same exception occured.

Finally I decoupled proxy and user control with queue/semaphor. Queue was monitored by a worker thread that deligated calls to user control

p.s. this queue should be inherited from “MarshalByObjectRef”.

Answer 1

If the exception is coming from the constructor, it means that you’re not creating this control instance from the UI thread. This can be fine but you have to make sure the Thread is an STA thread by calling .SetApartmentState(ApartmentState.STA) on the thread object before the thread is started.

This also means you have to have access to the thread object before its started so you cant do this on a threadpool thread.

The best way to avoid the problem though is probably to create the control on the main UI thread and then assign the Text value using the Dispatcher (or a Task on the UiScheduler). That way you’ll also avoid problems if the main thread needs to set, get or bind to the control, as that would cause a cross thread exception if the control was created on another thread

i’d advice against seriealizing the control this way if possible. doing that will generate a new object that is not attatched to any panels or some such, and the original control would not be updated. sadly you cant inheirit from MarshalByRefObject that would eliminate serialization since it would only pass a reference to the other domain.

If you can, call Foo separately and then pass the result to SetData in the original Appdomain