Скачать или смотреть How to Use completionHandler Results for a Navigation Link Destination in SwiftUI

Learn how to effectively use the result of a `completionHandler` to set the destination of a NavigationLink in SwiftUI with step-by-step instructions.
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How to Use completionHandler Results for a Navigation Link Destination in SwiftUI

Navigating between views is a common task in SwiftUI applications. However, when working with asynchronous operations, like making API calls, it can become a bit complicated. A frequent challenge developers face is how to pass the retrieved data from an asynchronous function, such as one that uses a completionHandler, into the destination view of a NavigationLink. In this guide, we'll explore a solution for this problem, primarily for iOS apps, utilizing Swift’s async/await syntax.

Understanding the Problem

The goal is to execute an asynchronous function (in this case, an API call) when a user taps a NavigationLink, and subsequently navigate to a new view using the data received from that function. The fundamental issue lies in how to manage the asynchronous nature of API calls while still ensuring a smooth user experience.

Example Code Breakdown:

You have a function, postProgramme, that calls a REST API and uses a completionHandler to return the result:

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And the NavigationLink setup that you are using appears as follows:

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The challenge is how to link the results of postProgramme to the destination view.

Solution: Utilizing Async/Await

Starting with iOS 15, Swift introduced the async/await capabilities which simplify working with asynchronous operations. Below, we detail the steps to refactor your code.

Step 1: Refactor Your API Function

First, we convert your postProgramme function to use async/await. This allows the function to return a Programme directly instead of using a completionHandler.

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Step 2: Update Your View to Handle State

Define a @ State variable in your parent view for the Programme object that you will pass to the ProgrammeDetailView.

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Step 3: Use Task to Call Async Function

Within the createNewProgramme function, you will use a Task to call your async function. This allows you to await the result and update the state variable once the call completes.

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Step 4: Pass Data to the Destination View

When setting up the NavigationLink, pass the programme state variable as a binding to ProgrammeDetailView.

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Step 5: Handle Binding in the Destination View

In ProgrammeDetailView, you'll define a @ Binding variable to receive the Programme object. You'll also need to consider how to present the view while waiting for the data to load.

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Conclusion

Implementing asynchronous operations in SwiftUI can initially seem daunting, especially when it involves navigation. However, with the introduction of async/await, the process has been significantly streamlined. By following the steps outlined in this post, you'll be able to smoothly pass data from a completionHandler to a NavigationLink destination, leading to a better user experience in your SwiftUI applications. Happy coding!