在SwiftUI中，无论你是针对iOS还是macOS，要获得屏幕的大小，你必须用GeometryReader Package 主视图。这样，你就可以轻松地访问它的大小。

struct ContentView: View {
    var body: some View {
        GeometryReader { geo in
            NavigationStack {
                HStack {
                    NavigationLink(destination: One(screenSize: geo.size)) {
                        Text("One")
                    }

                    NavigationLink(destination: Two(screenSize: geo.size)) {
                        Text("Two")
                    }
                }
            }
            .frame(width: geo.size.width, height: geo.size.height)
        }
    }
}

struct One: View {
    let screenSize: CGSize
    
    var body: some View {
        Text("I'm view One")
            .frame(width: screenSize.width, height: screenSize.height)
            .background(Color.green)
    }
}

struct Two: View {
    let screenSize: CGSize
    
    var body: some View {
        Text("I'm view Two")
            .frame(width: screenSize.width / 2, height: screenSize.height / 2)
            .background(Color.red)
    }
}

除了GeometricReader之外，您还可以使用UISscreen;

GeometryReader { geo in
   //Your code here
}
.frame(width: geo.size.width, height: geo.size.height)

Or 

.frame(width: UIScreen.main.bounds.width, height: 
 UIScreen.main.bounds.height)