Скачать или смотреть How to Get UIView Size in a Xamarin Forms Custom Renderer

Learn how to retrieve the `UIView` size in your Xamarin Forms custom renderer, ensuring precise positioning for your subviews.
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Understanding UIView Size in Xamarin Forms Custom Renderers

If you have been working with Xamarin Forms and custom renderers, you might find yourself needing to determine the size of a UIView for proper subview positioning. This can be particularly important when you want to leverage absolute positioning to achieve a specific layout. In this guide, we'll dive into how to get the size of a UIView within the context of a Xamarin Forms custom renderer.

The Problem

In a typical scenario, you might use the OnElementChanged method to check for changes to your custom view. However, if you try to get the size of your UIView within this method, you may find that the width and height are both returning zero. This is because the view's frame has not yet been calculated at this point in the lifecycle.

The Scenario

Consider this code snippet from your custom renderer:

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You may notice that checking uiView.Frame gives you zero for both width and height. So how do you capture the correct size of the UIView?

The Solution

To retrieve the UIView size accurately, you need to access it at a point in the lifecycle after the OnElementChanged method, where the view's frame has already been set. Let's explore a couple of effective methods to achieve this.

1. Utilizing the Draw Method

The Draw() method is an excellent place to determine the size of your view. By the time this method is called, UIKit has already determined the frame size of your UIView. Here’s how you can implement it:

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Notes:

This method allows you to access the correct frame size.

Ensure you call base.Draw(rect) to maintain the rendering of the view.

2. Using the LayoutSubviews Method

Another effective approach is to use the LayoutSubviews method. This method is invoked whenever the view's layout changes, and like the Draw method, it will give you the accurate frame size.

Here's a sample implementation:

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Output Example:

After implementing either of the above methods, you might see output like this when you run your application:

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This shows that you have successfully accessed the width of the view.

Conclusion

Understanding how to get the size of a UIView in a Xamarin Forms custom renderer is crucial for effective layout design, especially when working with absolute positioning. By leveraging the Draw or LayoutSubviews methods, you can reliably access the dimensions of your view after it has been properly laid out by UIKit.

Now you have the knowledge to ensure your subviews are positioned perfectly in your custom rendering solutions. Happy coding!