Swift游乐场预览中的SwiftUI大小看起来不正确

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
            .previewDevice(PreviewDevice(rawValue: "iPhone 12"))
            .previewDisplayName("iPhone 12")
    }
}

struct ContentView: View {
    var body: some View {
        GeometryReader { geometry in
            VStack {
                Text("Hello, SwiftUI!")
                    .frame(width: geometry.size.width / 2, height: geometry.size.height / 2)
            }
        }
    }
}

struct ContentView: View {
    @Environment(\.horizontalSizeClass) var sizeClass

    var body: some View {
        if sizeClass == .compact {
            // 紧凑布局
        } else {
            // 常规布局
        }
    }
}

struct ContentView: View {
    var body: some View {
        ZStack {
            Color.blue
            VStack {
                Text("Hello, SwiftUI!")
                    .foregroundColor(.white)
            }
        }
    }
}