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How to provide relative sizes using GeometryReader

Paul Hudson    @twostraws   

Updated for Xcode 12.0

Although it’s usually best to let SwiftUI perform automatic layout using stacks, it’s also possible to give our views sizes relative to their containers using GeometryReader. For example, if you wanted two views to take up half the available width on the screen, this wouldn’t be possible using hard-coded values because we don’t know ahead of time what the screen width will be.

To solve this, GeometryReader provides us with an input value telling us the width and height we have available, and we can then use that with whatever calculations we need. So, to get two views taking up equal width, we could divide the available space in half, like this:

struct ContentView: View {
    var body: some View {
        GeometryReader { geometry in
            HStack(spacing: 0) {
                Text("Left")
                    .frame(width: geometry.size.width / 2, height: 50)
                    .background(Color.yellow)
                Text("Right")
                    .frame(width: geometry.size.width / 2, height: 50)
                    .background(Color.orange)
            }
        }
    }
}

Note: GeometryReader doesn’t take into account any offsets or spacing further down in the view hierarchy, which is why there is no spacing on the HStack – if we allowed spacing in there, the views would be a little too large for the available space.

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