Скачать или смотреть Understanding How to Apply the Height of a GeometryReader Frame in SwiftUI

Discover how to effectively use the `GeometryReader` in SwiftUI to manage view sizes by applying `PreferenceKey` strategies. Learn the right way and avoid infinite cycles in size calculations!
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Understanding How to Apply the Height of a GeometryReader Frame in SwiftUI

When working with SwiftUI, you might have encountered the need to manage the size of your views dynamically based on their content. One common approach to achieving this is using GeometryReader. However, a question often arises—how do you effectively apply the height of a GeometryReader frame? This post will clarify the process and offer a structured solution to your problem.

The Problem

Using GeometryReader is intuitive for retrieving the available width of a container. Nonetheless, you may find yourself in situations where GeometryReader does not seem to accurately take into account the sizes of its child views. This can lead to confusion and bugs in your layout, particularly when you want to dynamically adjust a parent view to fit its content.

Question Breakdown

You might ask:

How do I obtain the size of a view and utilize it?

What is the best SwiftUI approach to avoid infinite loops in size calculations?

Your initial approach might look something like this:

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However, this method can create an infinite cycle since each size adjustment modifies the @ State property, which may continuously trigger updates.

The Solution: Using PreferenceKey

Instead of relying on @ State for recalculating view sizes, a more SwiftUI-idiomatic solution involves using PreferenceKey. Let's break this down into actionable steps:

1. Creating the PreferenceKey

First, you need to create a custom PreferenceKey that will help in storing and managing the size values.

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2. Using the PreferenceKey

Next, implement PreferenceKey in your desired view using GeometryReader to extract the size information:

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3. Retrieving the Size Value

Once you configure the PreferenceKey, you can retrieve the size value by using the .onPreferenceChange modifier:

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4. The Complete Code Example

Here’s how the complete implementation could look:

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5. Adding Convenience with Extensions

To make this more convenient, consider creating an extension for easy access to the size of various views:

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You can now call getSizeOfView like this:

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Conclusion

By following this structured approach with PreferenceKey, you can avoid infinite loops and effectively manage the heights of your GeometryReader frames in SwiftUI. This method ensures your views get dynamically sized based on their contents, maintaining an efficient and responsive layout.

Feel free to implement these strategies in your own SwiftUI projects and streamline your layout management process!