Swift UI DatePicker 不会更新 @ObservedObject 值

Question

我正在使用一个类来存储 @Published 变量，但是当我尝试将自定义 DatePicker 上选择的值传递给类中的 @ObservedObject 时，我收到以下错误：

TimePicker(time: self.$time.**timeSelected**)

无法转换“绑定”类型的值（又名 'Binding'）到预期的参数类型'TimeModel'

如何使用选择器值更新@ObservedObject？

完整代码：

struct ContentView: View {
    
    @ObservedObject var time = TimeModel()

    var body: some View {

        ZStack{
            VStack{
                TimePicker(time: self.$time.timeSelected)
                
                Text("You chose \(time.timeSelected/60) minutes")
            }
        }
    }
}

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

class TimeModel: ObservableObject{
     @Published var timeSelected: TimeInterval = 1.0
}
    

struct TimePicker: UIViewRepresentable {
    
    @ObservedObject var time = TimeModel()
    
    func makeUIView(context: Context) -> UIDatePicker {
        let datePicker = UIDatePicker()
        datePicker.datePickerMode = .countDownTimer
        datePicker.addTarget(context.coordinator,
                             action: #selector(Coordinator.updateTime),
                             for: .valueChanged)
        return datePicker
    }
    
    func updateUIView(_ datePicker: UIDatePicker, context: Context) {
        datePicker.minuteInterval = 5
        datePicker.countDownDuration = time.timeSelected
    }
    
    func makeCoordinator() -> Coordinator {
        Coordinator(self)
    }
    
    class Coordinator: NSObject {
        let parent: TimePicker
        
        init(_ parent: TimePicker) {
            self.parent = parent
        }
        
        @objc func updateTime(datePicker: UIDatePicker) {
            parent.time.timeSelected = datePicker.countDownDuration
        }
    }
}

Answer 1

你需要引用同样的TimeModel实例。

解决方案是将TimeModel 传递给TimePicker：

struct TimePicker: UIViewRepresentable {
    @ObservedObject var time: TimeModel // <- declare only

    ...
}

struct ContentView: View {
    @ObservedObject var time = TimeModel()

    var body: some View {
        ZStack {
            VStack {
                TimePicker(time: time) // <- pass `TimeModel` here

                Text("You chose \(time.timeSelected / 60) minutes")
            }
        }
    }
}

---

注意TimeInterval 指定时间以秒为单位，而不是分钟。

这一行：

@Published var timeSelected: TimeInterval = 1.0

实际上将默认时间设置为 1 秒。