Multicast delegation using NSProxy
Objective-C Ruby
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LBDelegateMatrioska.xcodeproj
LBDelegateMatrioska
LBDelegateMatrioskaTests
.gitignore
LICENSE
Podfile
README.md

README.md

LBDelegateMatrioska

This class is a subclass of NSProxy subclass that allows you to have multiple delegate helper objects (instead of the usual 1 to 1 relationship between the delegator and delegate).

Usage

You can init an LBDelegateMatrioska object with as many delegate objects you want

LBDelegateMatrioska *matrioska = [[LBDelegateMatrioska alloc] initWithDelegates:@[mapClusterDelegate, self]];

and the add this object as delegate

mapView.delegate = matrioska

In this way every time the MKMapView calls a delegate this call is forwarded to all the delegates respecting the array sorting (if you like the matrioska metaphor the mapClusterDelegate is the outer layer and is the first one called and then self)

The proxy object keep a weak reference to all the delegate objects, therefore is your responsibility to keep the objects alive with a strong reference. Anyway, by using an NSPointerArray I'm sure that if a delegate gets deallocated the reference inside the array is nil-ed and therefor doesn't crash the app.

There are just 2 basic rule and one limitation you have to keep in mind:

  • The proxy will respond YES to the respondToSelector: message if and only if at least one of the provided delegate objects respond YES to the same method.
  • The previous rule apply the same for conformsToProtocol:
  • If the delegate method is non-void returning method only the first delegate (that is able to respond to that method) is called and its return value is returned.

Why? / Use Case

I start develop this class because I was tasked to implement annotation clustering in MKMapView.

I found different libraries around the web but I wasn't really satisfied with the implementations: a lot of them subclass or swizzle method in MKMapView in order to hookup on the -mapView:regionWillChangeAnimated:/ -mapView:regionDidChangeAnimated: methods call.

So, the point is that I don't want to mess with delegator but I want to hook inside one of his delegate method call, and I want to still be able to receive all the delegate call (back to the map example: I still want that the ViewController that own MKMapView to be able to receive all the delegate call).

I found really interesting the ability to inject sort-of-plugin inside the delegate that split the responsibility of handling the delegate work. Again with my map example: I can easily "plug-in" the cluster behavior in any MKMapView (and eventually other behaviors to enhance the map view)

Unit Test

The class comes with a unit test coverage (using Kiwi). In order to have Kiwi and run the test you may want to run pod install and open the workspace (instead of the project file).

License

LBDelegateMatrioska is available under the MIT license. See the LICENSE file for more info.