启动SwiftUI计时器

import SwiftUI

struct ContentView: View {
    @State private var time = 0
    @State private var timer: Timer? = nil
    
    var body: some View {
        VStack {
            Text("Time: \(time)")
                .font(.largeTitle)
            
            Button(action: {
                if self.timer == nil {
                    self.timer = Timer.scheduledTimer(withTimeInterval: 1, repeats: true) { _ in
                        self.time += 1
                    }
                } else {
                    self.timer?.invalidate()
                    self.timer = nil
                }
            }) {
                Text(self.timer == nil ? "Start" : "Stop")
                    .font(.title)
                    .padding()
                    .background(Color.blue)
                    .foregroundColor(.white)
                    .cornerRadius(10)
            }
        }
    }
}

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