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Accepted
Duck
Asked: 2024-01-09 01:35:46 +0800 CST

访问未安装在视图上的 StateObject 对象

  • 772

关于这个问题还有其他答案，但没有一个答案可以解决这个问题，因为在我的例子中，我使用的是NSViewRepresentable可可视图，这不完全是一个 SwiftUI 视图。

我有这个代码：

struct MyObject: Hashable, Identifiable {
  let id: UUID = UUID()
  var name, brand: String
  init(name: String = "", brand: String = "") {
    self.name = varName
    self.brand = brand
  }
}

final class Model:ObservableObject {
  @Published var objects = (0..<3).compactMap {_ in
    return MyObject()
  }
}

struct ContentView: View {
  
  private let columns = [GridItem(.flexible()), GridItem(.flexible())]
  @StateObject private var model = Model()
    
  var body: some View {
    VStack{
      LazyVGrid(
        columns: columns,
        alignment: .center,
        spacing: 10,
        pinnedViews: []
      ) {
        ForEach($model.objects, id:\.id) {$object in
          MyTextField($initObject)
        }
      }
      
    }
    .padding(20)
  }
}

struct MyTextField: View {
  @Binding private var initObject:InitObject
  
  init(_ initObject:Binding<InitObject>) {
    _initObject = initObject
  }
  
  var body: some View {
    AppKitTextField(property: $initObject.name,
                    placeholder: "name",
                    fontName:"Avenir-Medium",
                    fontSize:18) { text in
    }
    
    MyAppKitTextField(property: $initObject.type,
                    placeholder: "type",
                    fontName:"Avenir-Medium",
                    fontSize:18)
      
    }
  }

问题是MyAppKitTextField a AppKit NSTextField NSViewRepresentable，如下所示：

public struct AppKitTextField: NSViewRepresentable {
  public typealias NSViewType = NSTextField
  @Binding var property: String

  public init(property: Binding<String>) {
    self._property = property
  }
    
  public class Coordinator: NSObject, NSTextFieldDelegate {
    @Binding private var text: String
    
    init(text: Binding<String>) {
      self._text = text
    }
  }

    public func makeNSView(context: NSViewRepresentableContext<AppKitTextField>) -> NSTextField {
        let textField = NSTextField()
        textField.delegate = context.coordinator
        textField.stringValue = property
        return textField
      }
      
      public func makeCoordinator() -> AppKitTextField.Coordinator {
        return Coordinator(text: $property)
      }
      
      public func updateNSView(_ nsView: NSTextField, context: Context) {
        nsView.stringValue = property
      }
    }
}

我的问题是线路

@Binding var property: String

当我尝试使用此视图时，我看到此错误：

Accessing StateObject's object without being installed on a View. This will create a new instance each time.
cocoa

1 个回答

  1. Best Answer

    我的第一个猜测是@Binding属性包装器不应该在Coordinator类中使用，因为它不是设计用于使用的View地方。@Binding相反，您可以使用闭Binding<String>包或仅使用闭包，因为您只需要设置即可。

    我的第二个猜测是这个错误：

    public func makeCoordinator() -> AppKitTextField.Coordinator {
    return Coordinator(text: $property)
}

    它应该是：

    public func makeCoordinator() -> AppKitTextField.Coordinator {
    return Coordinator() // make is only called once so there is no point in giving it an old version of the binding.
}

public func updateNSView(_ nsView: NSTextField, context: Context) {

    context.coordinator.textDidChange = nil // just to prevent endless updates depending on how your coordinator is designed

    nsView.stringValue = property

    // must also use the new version of the binding
    context.coordinator.textDidChange = { text
        self.property = text
    }
}

    仅供参考 Binding 只是一对 get/set 闭包，无需将 Binding 提供给协调器，因为它不需要 get，这就是textDidChange您应该从委托或操作处理程序中调用的仅 set 闭包的原因。

    • 2

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