Скачать или смотреть Understanding Why Your Protocol Type Never Gets a Value in Swift

Explore the issue of protocol types not receiving values in Swift. Learn how to fix initialization problems in your code with helpful examples!
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This video is based on the question https://stackoverflow.com/q/68001919/ asked by the user 'DrainOpener' ( https://stackoverflow.com/u/14440572/ ) and on the answer https://stackoverflow.com/a/68001960/ provided by the user 'Shehata Gamal' ( https://stackoverflow.com/u/5820010/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding Why Your Protocol Type Never Gets a Value in Swift

If you're working with Swift and protocols, you might have run into a frustrating issue: your protocol type never seems to get a value. This situation can leave you puzzled, especially when you think everything should be working. In this guide, we will break down the problem, identify the causes, and guide you through the solution step by step.

The Problem

Imagine you're trying to use a protocol in Swift to communicate between your view controllers and a struct. You have a protocol MyProtocol, and you want to utilize it within MyStruct. However, when you run your code, you notice that the delegate method myProtocolFunction never gets called, leaving you wondering why your setup isn’t working as expected.

Here's a brief look at the code that likely led to your confusion:

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From this code, it's evident that the issue lies in the initialization and timing of when you are trying to call the protocol function.

The Solution

Step 1: Moving Initialization of MyStruct

To solve the problem, you need to ensure that the myProtocol property is set before you make the function call. One way to achieve this is by passing the protocol instance when you initialize MyStruct.

Here's how you can adjust your ViewController class:

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Step 2: Modifying MyStruct’s Initialization

Now you need to modify the init method of MyStruct so that it accepts a MyProtocol instance right during its initialization. This means that you should set the protocol instance immediately when creating MyStruct:

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How This Works

Pass the Protocol Instance: By making myStruct aware of its protocol owner (the ViewController), you ensure that the myProtocol variable is initialized correctly before any function calls are made.

Immediate Call: In the restructured init, makeSomething() is called right after assigning myProtocol. This guarantees that the delegate method will not receive a nil reference.

Conclusion

By restructuring the initialization of your MyStruct and passing the MyProtocol instance right away, you can resolve the frustrating issues related to protocol values not being set correctly. This guide should give you a clearer understanding of how to effectively use protocols in Swift structures and how to ensure that delegation works as intended.

By following these steps, you can avoid the pitfalls associated with protocol delegation and improve the reliability of your Swift applications. Happy coding!