如何在SwiftUI中使弹出窗口的大小与其内容相适应

struct CustomAlertView: View {
    @Binding var isPresented: Bool
    
    var body: some View {
        GeometryReader { geometry in
            VStack {
                Text("弹出窗口的内容")
                    .font(.title)
                    .padding()
                
                Button("关闭") {
                    isPresented = false
                }
                .padding()
            }
            .frame(width: geometry.size.width * 0.8, height: geometry.size.height * 0.5)
            .background(Color.white)
            .cornerRadius(10)
        }
    }
}

struct ContentView: View {
    @State private var showAlert = false
    
    var body: some View {
        Button("显示弹出窗口") {
            showAlert = true
        }
        .alert(isPresented: $showAlert) {
            Alert(title: Text("弹出窗口"), content: {
                CustomAlertView(isPresented: $showAlert)
            })
        }
    }
}