How to support pinch to zoom in a UIScrollView

Swift version: 5.6

Paul Hudson @twostraws May 28th 2019

Making a scroll view zoom when you pinch is a multi-step approach, and you need to do all the steps in order for things to work correctly.

First, make sure your scroll view has a maximum zoom scale larger than the default of 1.0. You can change this in Interface Builder if you want, or use the maximumZoomScale property in code.

Second, make your view controller the delegate of your scroll view. Again, you can do this in Interface Builder by Ctrl-dragging from the scroll view to your view controller.

Third, make your view controller conform to the UIScrollViewDelegate protocol, then add the viewForZooming(in:) method, like this:

func viewForZooming(in scrollView: UIScrollView) -> UIView? {
    return someView
}

That's it for code, but make sure you create your layouts consistently – whether you use Auto Layout or not, you need to be careful to follow Apple's instructions.