Скачать или смотреть How to Properly Handle Completion Handlers in Swift

Learn how to efficiently call completion handlers from a second function in Swift. Enhance your asynchronous API calls with this simple guide.
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This video is based on the question https://stackoverflow.com/q/65486744/ asked by the user 'Santiago Alvarez' ( https://stackoverflow.com/u/4766621/ ) and on the answer https://stackoverflow.com/a/65487155/ provided by the user 'New Dev' ( https://stackoverflow.com/u/968155/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding Completion Handlers in Swift

In the world of asynchronous programming, completion handlers are essential for notifying when an operation finishes. If you are working with APIs or performing tasks in the background, you'll often encounter situations where you need to handle results once an operation completes. In this post, we will tackle a common problem in Swift programming—calling a completion handler from a second function.

The Problem: Not Being Able to Call Completion Handler

Let's begin with the scenario at hand. You have a function called doGet that handles API calls and has a completion handler to return the results. However, you want to create an additional function, getData, that also allows the completion handler to be used without calling doGet directly.

Here is the initial code you might have:

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This setup won’t work, as you cannot directly call a completion handler in getData without modifying how it’s structured.

The Solution: Modifying getData to Handle Completion

To solve the problem, we need to make getData accept a completion handler. This allows the function to asynchronously return results once doGet has completed its execution. Here’s the modified code:

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Explanation of Changes

Completion Handler Parameter: We've added a completion handler parameter to getData. This is necessary since getData will now also perform an asynchronous operation.

Calling doGet: Inside getData, we call doGet while providing it another closure to handle its completion. This closure receives the results from doGet.

Completion Forwarding: Finally, we invoke the completion handler of getData, passing along the parameters returned from doGet.

Putting it All Together

Now, your usage of getData in another class will work seamlessly:

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Key Takeaways

Remember that any function performing asynchronous tasks that needs to return a result must include a completion handler.

Passing along completion handlers from one function to another allows for better organization of code and clearer handling of results.

Conclusion

Getting comfortable with completion handlers in Swift can greatly enhance your app's performance and responsiveness. By creating intermediary functions like getData that manage completion handlers correctly, you can write cleaner, more maintainable code. Don’t hesitate to manipulate function signatures as needed to fit your architecture and design.

With this guide, you should now be equipped to handle completion handlers effectively in your Swift programs. Happy coding!