SwiftUI - @Published 属性未从协调器更新视图答案

【问题标题】：SwiftUI - @Published property is not updating view from coordinatorSwiftUI - @Published 属性未从协调器更新视图
【发布时间】：2020-10-21 11:16:10
【问题描述】：

我在UISearchBar 周围使用了一个包装器，当将@Published 属性传递到此SearchBar 包装器与TextField 时，我看到了不同的行为。

两者都按预期更新@ObservedObject var query = Query() 类@Published var input 属性，但只有TextField 更新SearchSheet 视图。我希望在 input 已在 SearchBar 中更改时更新视图，类似于从 TextField 更新的方式。

编辑：我已更新我的问题以包含 ContentView，其中看起来此问题特定于从 NavigationBarItem 中的 Button 调用工作表时。

struct ContentView: View {
    @State var showingSearch = false
    
    var body: some View {
        NavigationView {
            VStack {
                Text("Hello World")
            }
            .navigationBarItems(trailing:
                Button(action: {
                    self.showingSearch.toggle()
                }) {
                    Image(systemName: "magnifyingglass")
                }
                .sheet(isPresented: $showingSearch) {
                    SearchSheet(isPresented: self.$showingSearch)
                }
            )
        }
    }
}

class Query: ObservableObject {
    @Published var input = "" {
        didSet {
            // Called as expected in both cases but only TextField updates the SearchSheet view.
        }
    }
}

struct SearchSheet: View {
    @ObservedObject var query = Query()

    var body: some View {
        VStack {
            // Does not update the SearchSheet view. I would like it understand why and how to update it.
            SearchBar(text: $query.input, placeholder: "Search")
            // Does update the SearchSheet view.
            TextField("Search", text: $query.input)

            Text("\(query.input)")
        }
    }
}

import SwiftUI

struct SearchBar: UIViewRepresentable {

    @Binding var text: String
    var placeholder: String

    class Coordinator: NSObject, UISearchBarDelegate {

        @Binding var text: String

        init(text: Binding<String>) {
            _text = text
        }

        func searchBar(_ searchBar: UISearchBar, textDidChange searchText: String) {
            text = searchText
        }
    }

    func makeCoordinator() -> SearchBar.Coordinator {
        return Coordinator(text: $text)
    }

    func makeUIView(context: UIViewRepresentableContext<SearchBar>) -> UISearchBar {
        let searchBar = UISearchBar(frame: .zero)
        searchBar.delegate = context.coordinator
        searchBar.placeholder = placeholder
        searchBar.searchBarStyle = .minimal
        searchBar.autocapitalizationType = .none
        return searchBar
    }

    func updateUIView(_ uiView: UISearchBar, context: UIViewRepresentableContext<SearchBar>) {
        uiView.text = text
    }
}

struct SearchBar_Previews: PreviewProvider {
    @State private static var text = ""
    
    static var previews: some View {
        SearchBar(text: $text, placeholder: "Search")
    }
}

【问题讨论】：

在 Xcode 11.4 / iOS 13.4 上可以正常工作
谢谢@Asperi，你说得对，在一个新项目中这似乎确实按预期工作。我已更新以包含导致此失败的 ContentView。

标签： ios swift swiftui

【解决方案1】：

将工作表的显示从navigationBarItems 移出可解决此问题。当时我认为这是一个错误。

.navigationBarItems(trailing:
    Button(action: {
        self.showingSearch.toggle()
    }) {
        Image(systemName: "magnifyingglass")
    }
)
.sheet(isPresented: $showingSearch) {
    SearchSheet(isPresented: self.$showingSearch)
}

【讨论】：