使离屏SwiftUI视图居中

import SwiftUI

struct CenteredOffscreenView: View {
    var body: some View {
        GeometryReader { geometry in
            ZStack {
                // 离屏视图
                Color.green
                    .frame(width: 100, height: 100)
                    .background(Color.blue)
                    .alignmentGuide(.center) { d in
                        -d[.leading] + geometry.size.width / 2
                    }
                    .alignmentGuide(.center) { d in
                        -d[.top] + geometry.size.height / 2
                    }
                
                // 主视图
                Text("Main View")
                    .foregroundColor(.white)
                    .font(.largeTitle)
            }
        }
    }
}

struct ContentView: View {
    var body: some View {
        CenteredOffscreenView()
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}