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Swift delegate design pattern – The.Swift.Dev.



The delegate design pattern is a relatively easy way to communicate between two objects through a common interface, protocol in Swift.


Implementation delegation in Swift

You'll need a delegate protocol, a delegator who actually delegates out de opgaver og en delegeret objekt som implementerer den delegerede protokol og gør det egentlige arbejde, som blev anmodet af "bossen". Let's translate this into human.

The client reports a bug. The project manager creates an issue and tells one of the developers to fix the problem asap.

See? That's delegation. At some point an event happened, so the delegator (manager) utilized an external resource (a developer) using a common interface (issue describing the problem for both parties) to do something (fix the 🐛).

To demonstrate how Delegation works in real life I made a pretty simple example. I'm going to use a similar approach (because Xcode playgrounds are still freezing every 1

-5 minutes) like I did for the command pattern, but the purpose of this one is going to be almost completely different, because we're talking about delegation. 😅

This is how you can create your own delegate pattern in Swift. You can imagine that Apple is doing the same thing under the hood, with UICollectionViewDataSource UICollectionViewDelegate etc. You only have to implement the delegate, they will provide the protocol and the delegator. 🤔


Weak properties, delegates and classes

Memory management is a very important thing, so it's worth mentioning that all the class delegates should be weak properies, or you'll create a really bad reatin cycle. 😱

Here is the altered Swift code snippet, but now using a class as the delegate. Du skal bare forandre din protokol et lille stykke og ejendommen inden for delegatoren. Bruk alltid svaga delegatvariable hvis du skal tilordne en klasse som en delegat. ⚠️

As you can see delegation is pretty easy, but it can be dangerous. It helps decoupling by providing a common interface that can be used by anyone who implements the delegate (sometimes data source) protocol. There are really amazing articles about delegates, if you would like to know more about this pattern, you should check them out.


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