Objective-C delegate multiplexing
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MultiDelegate Iterate delegates using a copy Mar 24, 2016
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MultiDelegate is a delegate multiplexing class for Objective-C. In other words, it will dispatch delegate methods to multiple objects, instead of being restricted to a single delegate object. You can also use it as a generic method dispatch mechanism. For more information see the blog post.

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Suppose you have a UITableView and you want to implement the data source using two separate classes: one is the actual data source implementing the tableView:numberOfRowsInSection: method and the other one is the cell factory implementing the tableView:cellForRowAtIndexPath: method to construct the cells.

First create an AIMultiDelegate instance. You need to keep a strong reference to this instance because most objects don't retain their delegates:

_multiDelegate = [[AIMultiDelegate alloc] init];

Then add all the actual delegates to the _multiDelegate object:

[_multiDelegate addDelegate:self];
[_multiDelegate addDelegate:_dataSource];

Finally set the table's data source as the delegate multiplexer:

self.tableView.dataSource = (id)_multiDelegate;

See the example project for the full source.


Keep this in mind

  • Every method invocation will be forwarded to each object in the list in the order they were added.
  • If a method returns a value the return value will be from the last object that responded to the method. For example if object A implements method getInt by returning 1, object B implements getInt by returning 2 and object C doesn't implement getInt, calling getInt on an AIMultiDelegate containing A, B and C (in that order) will return 2.
  • AIMultiDelegate doesn't keep strong references to the objects added to it.
  • Some objects only call respondsToSelector: when you first set the delegate to improve performance, so make sure you add all your delegates to the AIMultiDelegate before you set it as the delegate.


If you are using CocoaPods, add this to your Podfile:

pod 'MultiDelegate'

Otherwise add AIMultiDelegate.h/.m to your project.