Ios SwiftUI TextField 在焦点上清除 Double 类型的值，在取消 Select 时恢复

Scenario:
In SwiftUI, my TextField has a Double value. On tapping/focusing the TextField the current Double value is cleared, to allow the user to easily enter a new value without having to select and delete the current value. If the user does not enter a new value, the old value is restored on deselect.

发行

利用.focused()和.onChange(of:)似乎不可能做到这一点.下面的代码正确清除了该值(在控制台中可见).但是，更改不会反映在用户界面中.通过在TextField上使用.id()来强制更新UI会取消 Select TextField，从而使此解决方法毫无用处.

为什么用户界面没有从更改更新为TextField值属性？

struct ContentView: View {
    
    @FocusState var focus: Bool
    @State var test: Double? = 100
    @State var id: UUID = UUID()
    
    var body: some View {
        VStack {
            TextField("Placeholder", value: $test, format: .number)
                .id(id)
                .focused($focus)
                .onChange(of: focus, perform: { editing in
                    var oldValue: Double? = test
                    if editing {
                        self.$test.wrappedValue = nil
                        self.$id.wrappedValue = UUID()
                    } else {
                        if test == nil {
                            self.$test.wrappedValue = oldValue
                            self.$id.wrappedValue = UUID()
                        }
                    }
                })
        }
        .padding()
    }
}

有没有办法用SwiftUI的TextField来做到这一点？