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Learn how to effectively use magnification gestures in SwiftUI to maintain the scale of your images while pinch zooming.
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This video is based on the question https://stackoverflow.com/q/73743757/ asked by the user 'Duck' ( https://stackoverflow.com/u/316469/ ) and on the answer https://stackoverflow.com/a/73744101/ provided by the user 'vacawama' ( https://stackoverflow.com/u/1630618/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Enhancing Your SwiftUI Image: Pinch Zoom Without Losing Scale

If you’re working with images in SwiftUI and want to implement pinch-to-zoom functionality, you might encounter a common issue: after scaling up an image with a pinch gesture, the scale resets to 1 when you try to zoom again. This can be frustrating and disrupts the user experience. In this guide, we'll explore why this happens and how to fix it so that your image maintains its scale even after lifting your fingers.

Understanding the Problem

When you apply a pinch gesture to an image in SwiftUI, it’s common to want the image to "remember" its current scale instead of reverting to a default scale of 1. The original code you may be using can cause the following undesirable behavior:

The image is scaled correctly when you pinch.

Upon lifting your fingers, the image sticks to a larger scale.

However, the next pinch gesture resets the scale back to 1, which is not the intended functionality.

So, how can we solve this problem?

The Solution: Managing Scale State

To maintain the scale properly, we need to track the image's scale in two separate ways:

Permanent Scale (imageScale): This will store the cumulative scale of the image that persists between gestures.

Current Magnification Value (magnifyBy): This will represent the scale for the ongoing gesture.

Implementation Steps

Here’s how you can modify your code to achieve the desired behavior:

Declare Two State Variables: Start by declaring state variables to hold the scale values.

Apply Scale Effect: Use a combined effect of permanent scale and the current magnification value on the image.

Gesture Handling: Manage the scaling logic within the gesture's lifecycle to update the scale correctly when you start and end the gesture.

Modified Code Example

Here’s an example of how to implement these steps in your SwiftUI view:

[[See Video to Reveal this Text or Code Snippet]]

Explanation of the Code

Image Setup: The image is set as resizable and padded to create a suitable display area.

Scale Effect: The scaleEffect modifier now combines imageScale and magnifyBy. This allows the image to visually scale properly during and after pinch gestures.

Gesture Logic:

On Change: As you pinch, magnifyBy updates to the current gesture's magnitude.

On End: When the gesture ends, imageScale is updated by multiplying it with the final value of the pinch, and magnifyBy resets to 1 for the next gesture.

Conclusion

By managing the scale state properly with two variables, you can ensure that your images maintain their zoom level across pinch gestures in SwiftUI. No more resetting to a scale of 1 and frustrating your users!

Incorporate this technique into your SwiftUI projects, and enjoy a smoother, more intuitive image zooming experience!