четверг, 11 августа 2011 г.

Execute Caliburn coroutine in action pipeline without UI trigger

Seems rather easy, isn't it?

Just put it into Presenter's Execute method and the did is done. Well, should it be like that I wouldn't wake up in the night and write this stuff!
Let's see what's there in Execute:

So, it just packs every single coroutine it has in SequentialResult and execute 'em. No filters pipeline used, no routedMessage. None of your neat filters applied to these coroutines.

You might ask what is the difference with executing coroutines as a result of some UI action, be it a routed event or a command. The answer is in the Caliburn.PresentationFramework.Actions namespace.
To be prrecise it is an Action Execute overloaded method that in simple case of SynchronousAction does the following:

namely calls preprocessor filters, delegates a call to method that might be returning coroutine, handles errors with rescue filters, calls postprocessor filters. That is a filter pipeline I am talking about.
Well, seems that Caliburn has everything I need. And all I have to do is just use it.

As header states there is no UI trigger, i.e. I want to execute a coroutine when nobody clicked a button, but rather on some external trigger. As an example, consider model update with call to any data storage during Presenter initialization stage.

Enter DegenerateMessage. This intellectual piece of code is a data container that is being handed to participants on courutine call pipeline in order to hint what was the original method name called.

Another intellectual piece of code is DegenerateMessageTrigger. It is so damn smart that it knows that in order to trigger an action it has to pass a message to message handler!

And yet another piece is a DegenerateMessageHandler. It really shouldn't be called that way as it performs really complicated things. Namely, it creates an ActionHost and when Process is called converts DegenerateMessage to an ActionMessage and put it into the standard Caliburn action pipeline.

If it seems like dancing on your head, then know that you are not alone. But wait, there is another part I forgot to mention. It is a simple interface IResultExecutor aimed to hide all that smart code under two methods accepting Expressions with lambdas calling methods that return coroutines.

Oh, and there is yet another thing. With Caliburn Micro you can accomplish the same with only one line of code.


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