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SwiftUI:使用@FocusState。与视图初始化器绑定

swiftui swift

Z S · 技术社区 · 昨天

我有一个观点 @FocusState 我想传递到子视图中。对于子视图,我使用 @FocusState.Binding 。如果我不使用自定义初始化器,这可以很好地工作。。。但我无法弄清楚它如何与自定义视图初始化器一起工作的语法,出于其他原因,我需要它。

以下是有效的代码:

struct TestListButtonsAndListFocusView: View {
    
    @FocusState var buttonFocusState: ButtonState?
    @ObservedObject var viewModel: ViewModel = ViewModel()
    
    var body: some View {
        TestListView(viewModel: viewModel, bindedFocusButtonState: $buttonFocusState) // for custom init, replace with following line
        //TestListView(viewModel: viewModel, focusButtonState: $buttonFocusState) // 1. Uncomment this for custom initializer
    }
}

struct TestListView: View {
    @State private var items1: [TimedItem] = [
        TimedItem(number: 1, timestamp: "2024-11-20 10:00"),
        TimedItem(number: 2, timestamp: "2024-11-20 11:00"),
        TimedItem(number: 3, timestamp: "2024-11-20 12:00")
    ]
    
    @ObservedObject var viewModel: ViewModel
    @FocusState.Binding var bindedFocusButtonState: ButtonState?
    
    @State var selectedItem: TimedItem.ID?
    
    var body: some View {
        List(items1, selection: $selectedItem) { item in
            ContentListItemView(item: item)
        }
        .onChange(of: bindedFocusButtonState) {
            if let bindedFocusButtonState {
                print("TestListView - bindedListFocusState has changed to \(bindedFocusButtonState)")
                if bindedFocusButtonState == .one && selectedItem == nil {
                    selectedItem = items1.first?.id
                }
            } else {
                print("ListOneView - bindedListFocusState has changed to nil")
            }
        }
    }
    
    // 2. Uncomment this
    /*init(viewModel: ViewModel, focusButtonState: FocusState<ButtonState?>.Binding) {
        // how to pass in @FocusState.Binding?
        self.viewModel = viewModel
        self.bindedFocusButtonState = focusButtonState
        // Error: Cannot assign value of type 'FocusState<ButtonState?>.Binding' to type 'ButtonState?'
    }*/
}

public class ViewModel: NSObject, ObservableObject {
    
    @Published public var selectedButton: ButtonState? = ButtonState.one
}

public enum ButtonState: Int, CaseIterable, Hashable, Identifiable {
    
    public var id: Self {
        return self
    }
    case one, two, three
}

    
#Preview {
    TestListButtonsAndListFocusView()
}

但是,如果我取消注释自定义初始化器的行,然后取消注释 TestListButtonsAndListFocusView 要使用自定义初始化器,语法错误,我得到错误:

错误:无法分配“FocusState<”类型的值;按钮状态>。绑定' 键入“ButtonState?”

我不确定如何初始化 @焦点状态。结合 这种方式。我知道如果我使用它,它就会起作用 var bindedFocusButtonState: FocusState<ContactTabStyle?>.Binding 相反,然后在初始化器中也使用它。但我真的很想弄清楚如何使用新的 @焦点状态。结合 使用自定义初始化器,因为它避免了访问 wrappedValue 并且更容易观察 onChange

1 回复 | 直到昨天

Sweeper 昨天

您应该为下划线前缀属性赋值 _bindedFocusButtonState .

self._bindedFocusButtonState = focusButtonState

这是实际包含 FocusState.Binding . bindedFocusButtonState 另一方面,它实际上是一个返回的计算属性 _bindedFocusButtonState.wrappedValue .

特别是,线

@FocusState.Binding var bindedFocusButtonState: ButtonState?

声明三属性:

private var _bindedFocusButtonState: FocusState<ButtonState?>.Binding

var bindedFocusButtonState: ButtonState? {
    get { _bindedFocusButtonState.wrappedValue }
    set { _bindedFocusButtonState.wrappedValue = newValue }
}

var $bindedFocusButtonState: FocusState<ButtonState?>.Binding {
    get { _bindedFocusButtonState.projectedValue }
}