Weak event pattern in MonoTouch

Question

I used to develop iOS applications using the Objective-C language and relied on the dealloc method to perform some cleanup / unregister tasks in my application. Now in MonoTouch (garbage collector) this is no longer an option.

Suppose I have a UIViewController that adds a View property of an instance of the MyView subclass ( UIView ) as a subordinate to it. MyView , in turn, registers to receive some events from another manager / global object so that it knows how to update it accordingly (for example: onlineProfilesManager.Refreshed += () => <update UI with the new state>; ).

As long as MyView displayed on the screen, everything is in order. However, I need to know when it is removed from the screen so that I can unregister MyView from the event handler.

In Obj-C, this can simply be done in the dealloc method, because when the screen changes, the UIViewController freed up → MyView is removed from it supervision, and then the MyView dealloc method is MyView .

In Monotouch, I no longer have this deterministic stream. I tried to put some print instructions in the destructors of UIViewController and MyView , but they are never called (the reason is that MyView is still registered for the event handler, since I do not know when / how to unregister it will never be released).

Does anyone know what a “pattern” is for handling such situations in MonoTouch? I think that I am missing a fundamental concept and problems with application development.

Thanks in advance.

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EDIT I am editing my question because it seems that the solution to my problem is a Weak event pattern , but I did not find an implementation for the MonoTouch platform.

Does anyone know how I can use a weak event pattern in MonoTouch?

Answer 1

The best way to handle events is to deregister from ViewWillDisappear and register them with ViewWillAppear. This means that you cannot use anonymous methods, although you do not have a reference to the method to unregister it.

If what you need is not right for you, you can do something similar to this http://sgmunn.com/blog/2012/05/non-gcd-event-handlers/

Greetings.

Answer 2

If you are looking for weak events, you can try your implementation of Messenger here .

It is inspired by what is available in TinyIoC , but I reimplemented it to use less reflection, etc.