Скачать или смотреть How to Create a # Preview with Async Code in SwiftUI

Discover how to enhance your SwiftUI experience by creating a `# Preview` using async/await values. Learn step-by-step solutions to common issues with previews in SwiftUI.
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Creating a # Preview with Async Code in SwiftUI

SwiftUI has revolutionized how developers build user interfaces in Apple's ecosystem by providing a more declarative approach. However, when it comes to asynchronous operations, such as fetching data, developers often face challenges—especially when trying to create effective previews. In this post, we will explore how to create a # Preview that utilizes async/await in SwiftUI.

The Problem

Imagine you are working on a SwiftUI project where you need to use live data fetched asynchronously for your previews. The challenge arises when you attempt to access an async function directly within the # Preview. You might encounter the following error message:

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This issue happens because the preview environment does not inherently support async operations in the same way a normal asynchronous context does. This can be frustrating, especially since the aim is to closely replicate the app's behavior without creating dummy static data.

The Solution

To address this issue, we can take a structured approach by encapsulating the async operations within a separate View struct defined inside the # Preview. This allows you to leverage the power of @ State variables to manage the async data fetching seamlessly. Here’s how to implement this solution step by step:

Step 1: Define Your SwiftUI View

First, let's define our SwiftUI view that will utilize the async data:

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Step 2: Set Up the Asynchronous Preview

Next, we need to create a new # Preview that accommodates async code. We will encapsulate this logic in a struct that conforms to View.

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Step 3: Utilize Your Asynchronous Function

Ensure you have your asynchronous function defined within a class, as shown below:

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Important Considerations

Struct Ownership: The AsyncTestView struct can either be defined directly inside the # Preview or above it. Just bear in mind that placing it within the # Preview ensures unused code is not included in the final product.

Naming: If your project utilizes multiple # Preview macros, it might be wise to give them meaningful names. This practice enhances your code's readability and maintainability.

Conclusion

Incorporating async data fetching into your SwiftUI previews allows for a more accurate representation of your app's behavior. By utilizing the @ State variable alongside a custom view struct, you can successfully resolve the challenge of calling asynchronous functions in your previews. Happy coding!