Layout and geometry: Wrap up

Paul Hudson    @twostraws    February 21st 2024

I hope this smaller technique project proved a welcome break after our long app projects, but I hope even more that you’re really starting to have a good mental model of how SwiftUI’s layout system works. That three step layout system might sound simple, but it takes time to fully understand the ramifications it has.

As for GeometryReader, it’s one of those things you can get by perfectly fine without even thinking about, and that’s fine. But sometimes – just sometimes – you need a little extra power that you can't get from container relative frames or other SwiftUI options, and that's where GeometryReader can come to the rescue.

Review what you learned

Anyone can sit through a tutorial, but it takes actual work to remember what was taught. It’s my job to make sure you take as much from these tutorials as possible, so I’ve prepared a short review to help you check your learning.

Click here to review what you learned in this project.

Challenge

One of the best ways to learn is to write your own code as often as possible, so here are three challenges for you to complete to experiment with your knowledge of GeometryReader.

First, put your ContentView back to the spinning color rows example we had:

struct ContentView: View {
    let colors: [Color] = [.red, .green, .blue, .orange, .pink, .purple, .yellow]

    var body: some View {
        GeometryReader { fullView in
            ScrollView(.vertical) {
                ForEach(0..<50) { index in
                    GeometryReader { proxy in
                        Text("Row #\(index)")
                            .font(.title)
                            .frame(maxWidth: .infinity)
                            .background(colors[index % 7])
                            .rotation3DEffect(.degrees(proxy.frame(in: .global).minY - fullView.size.height / 2) / 5, axis: (x: 0, y: 1, z: 0))
                    }
                    .frame(height: 40)
                }
            }
        }
    }
}

With that done:

1. Make views near the top of the scroll view fade out to 0 opacity – I would suggest starting at about 200 points from the top.
2. Make views adjust their scale depending on their vertical position, with views near the bottom being large and views near the top being small. I would suggest going no smaller than 50% of the regular size.
3. For a real challenge make the views change color as you scroll. For the best effect, you should create colors using the Color(hue:saturation:brightness:) initializer, feeding in varying values for the hue.

Each of those will require a little trial and error from you to find values that work well. Regardless, you should use max() to handle the scaling so that views don’t go smaller than half their size, and use min() with the hue so that hue values don’t go beyond 1.0.