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Asked: 2025-02-07 03:41:20 +0800 CST

SwiftUI：将 @FocusState.Binding 与视图初始化程序结合使用

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我有一个带有 的视图@FocusState，我想将其传递到子视图中。对于子视图，我使用@FocusState.Binding。如果我不使用自定义初始化程序，这可以正常工作……但我无法弄清楚它如何与自定义视图初始化程序一起工作的语法，出于其他原因我需要它。

这是有效的代码：

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程序的行，然后取消注释TestListButtonsAndListFocusView使用自定义初始化程序的行，则语法错误，并且会出现错误：

错误：无法将“FocusState<ButtonState?>.Binding”类型的值分配给“ButtonState?”类型

我不确定如何以@FocusState.Binding这种方式初始化。我知道如果我使用var bindedFocusButtonState: FocusState<ContactTabStyle?>.Binding，然后在初始化程序中使用它，它会起作用。但我真的很想弄清楚如何将 new@FocusState.Binding与自定义初始化程序一起使用，因为它避免了必须访问wrappedValue并且更容易观察onChange

swift

1 个回答

  1. Best Answer

    您应该分配给以下划线为前缀的属性_bindedFocusButtonState。

    self._bindedFocusButtonState = focusButtonState

    这是实际包含 的属性FocusState.Binding。bindedFocusButtonState另一方面，实际上是返回 的计算属性_bindedFocusButtonState.wrappedValue。

    尤其是这一行

    @FocusState.Binding var bindedFocusButtonState: ButtonState?

    声明三个属性：

    private var _bindedFocusButtonState: FocusState<ButtonState?>.Binding

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

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