如何在SwiftUI中显示警报视图或自定义覆盖

struct ContentView: View {
    @State private var showAlert = false
    
    var body: some View {
        Button("显示警报") {
            showAlert = true
        }
        .alert(isPresented: $showAlert) {
            Alert(
                title: Text("警报标题"),
                message: Text("这是一条警报消息"),
                primaryButton: .default(Text("确定")),
                secondaryButton: .cancel(Text("取消"))
            )
        }
    }
}

struct ContentView: View {
    @State private var showSheet = false
    
    var body: some View {
        Button("显示自定义覆盖") {
            showSheet = true
        }
        .sheet(isPresented: $showSheet) {
            Text("这是一个自定义覆盖视图")
                .font(.title)
                .padding()
        }
    }
}