在体外访问 SwiftUI 视图中的状态变量

Question

我有一个内容视图，我想动态跟踪高度。

我已经实现了这个解决方案，但是我遇到了这个异常：

Fatal error: Accessing State outside View.body: file

我该怎么做才能让 keyboardHeight 动态更新我的 UI

struct ContentView: View {

    @State var keyboardHeight: CGFloat = 0
    var cancellables: Set<AnyCancellable> = []

    init() {
        NotificationCenter.default.publisher(for: UIResponder.keyboardWillChangeFrameNotification)
        .merge(with: NotificationCenter.default.publisher(for: UIResponder.keyboardWillHideNotification))
        .compactMap({ notification in
          guard let keyboardFrameValue: NSValue = notification.userInfo?[UIResponder.keyboardFrameEndUserInfoKey] as? NSValue else { return nil }
          let keyboardFrame = keyboardFrameValue.cgRectValue
          if keyboardFrame.origin.y == UIScreen.main.bounds.height {
            return 0
          } else {
            return keyboardFrame.height - (UIApplication.shared.windows.first?.safeAreaInsets.bottom ?? 0)
          }
        })
        .assign(to: \.keyboardHeight, on: self)
        .store(in: &cancellables)
    }

    var body: some View {
        VStack{
            ZStack(alignment: Alignment.bottom) {
                List {
                    Text("Default text").foregroundColor(Color.red)
                }
                TextField("Placeholder", text: .constant(""))
                    .frame(minHeight: 30)
                    .cornerRadius(8.0)
                    .padding(10)
                    .background(Color.blue)
            }
            Spacer()
                .frame(height: keyboardHeight)
        }
    }
}

Answer 1

错误消息几乎准确地说明了问题所在。但是，尽管您不能访问主体函数（或从主体调用的函数）外部的状态变量，但您可以访问可观察对象。因此，只需将 @State 更改为 @ObservedObject 并定义一个微小的 class，就足以使其工作。

请注意，此解决方案旨在保持您的工作流程理念完整无缺。虽然，还有其他方法可以完成同样的事情。

import SwiftUI
import Combine

class Model: ObservableObject {
    @Published var keyboardHeight: CGFloat = 0
}

struct ContentView: View {
    @ObservedObject var model = Model()

    var cancellables: Set<AnyCancellable> = []

    init() {
        NotificationCenter.default.publisher(for: UIResponder.keyboardWillChangeFrameNotification)
            .merge(with: NotificationCenter.default.publisher(for: UIResponder.keyboardWillHideNotification))
            .compactMap({ notification in
                guard let keyboardFrameValue: NSValue = notification.userInfo?[UIResponder.keyboardFrameEndUserInfoKey] as? NSValue else { return nil }

                let keyboardFrame = keyboardFrameValue.cgRectValue

                if keyboardFrame.origin.y == UIScreen.main.bounds.height {
                    return 0
                } else {
                    return keyboardFrame.height - (UIApplication.shared.windows.first?.safeAreaInsets.bottom ?? 0)
                }
            })
            .assign(to: \.keyboardHeight, on: model)
            .store(in: &cancellables)
    }

    var body: some View {
        VStack{
            ZStack(alignment: Alignment.bottom) {
                List {
                    Text("Default text").foregroundColor(Color.red)
                }
                TextField("Placeholder", text: .constant(""))
                    .frame(minHeight: 30)
                    .cornerRadius(8.0)
                    .padding(10)
                    .background(Color.blue)
            }
            Spacer()
                .frame(height: model.keyboardHeight)
        }
    }
}

在体外访问 SwiftUI 视图中的状态变量

Accessing state variable in SwiftUI View outside the body

swiftui

combine