为什么属性 Observer 不适用于 SwiftUI 中的 Picker

Question

当我使用按钮（ontapGesture）更改选定的驱动器时，它会打印“值已更改”，但是当我使用选择器更改值时，didset 功能不起作用。

enum WheelDrive: String, CaseIterable, Identifiable {
    case frontdrive
    case reardrive
    case Fourwheeldrive
    case Neutral
    var id: String { self.rawValue }
}

@State var selecteddrive = WheelDrive.Fourwheeldrive {
    willSet(newValue){ print("value changed")}
}
Picker(selection: $selecteddrive, label: Text("WheelDrive")) {
    Text("前驱").tag(WheelDrive.frontdrive)
        .foregroundColor(.white)
    Text("后驱").tag(WheelDrive.reardrive)
        .foregroundColor(.white)
    Text("四驱").tag(WheelDrive.Fourwheeldrive)
        .foregroundColor(.white)
    Text("滑行").tag(WheelDrive.Neutral)
        .foregroundColor(.white)
}

Answer 1

使用自定义绑定

Picker(selection: Binding(get: {selecteddrive}, set: {selecteddrive = [=10=]}), label: Text("WheelDrive")) { //<-- Here
    Text("前驱").tag(WheelDrive.frontdrive)
        .foregroundColor(.white)
    Text("后驱").tag(WheelDrive.reardrive)
        .foregroundColor(.white)
    Text("四驱").tag(WheelDrive.Fourwheeldrive)
        .foregroundColor(.white)
    Text("滑行").tag(WheelDrive.Neutral)
        .foregroundColor(.white)
}

或者您可以使用 .onChange 获取价值。

Picker(selection: $selecteddrive, label: Text("WheelDrive")) {
    Text("前驱").tag(WheelDrive.frontdrive)
        .foregroundColor(.white)
    Text("后驱").tag(WheelDrive.reardrive)
        .foregroundColor(.white)
    Text("四驱").tag(WheelDrive.Fourwheeldrive)
        .foregroundColor(.white)
    Text("滑行").tag(WheelDrive.Neutral)
        .foregroundColor(.white)
}
.onChange(of: selecteddrive, perform: { (selecteddrive) in //<- Here
    print(selecteddrive)
})

为什么属性 Observer 不适用于 SwiftUI 中的 Picker

Why Property Observer does not work for Picker in SwiftUI

picker

ios

swift

swiftui

为什么 属性 Observer 不适用于 SwiftUI 中的 Picker

Why Property Observer does not work for Picker in SwiftUI

picker

ios

swift

swiftui

为什么属性 Observer 不适用于 SwiftUI 中的 Picker