如何在自定义 SwiftUI 视图中设置文本字段和按钮

Question

我正在尝试将我的 openweathermap 应用程序中的文本字段和按钮配置为在其自己的视图中，而不是在主要内容视图中。在 TextFieldView 中，按钮的操作设置为调用 API 响应。然后，来自响应的天气数据被填充到基于 sheet 的 DetailView 上，它由 TextFieldView 中的按钮触发。我将 sheet 中的 ForEach 方法配置为 return 添加到 WeatherModel 数组的最后一个城市（从技术上讲，这将是最近输入文本字段的城市），然后填充 sheet - 基于 DetailView，带有该城市的天气数据。以前，当我在 ContentView 中设置包含文本字段、按钮和 sheet 控件的 HStack 时，Sheet 会正确显示刚刚输入文本字段的城市的天气。将这些项目移动到单独的 TextFieldView 后，ForEach 方法似乎已停止工作。相反，在文本字段中输入城市名称后 returned 的天气信息显示错误。例如，如果我在文本字段中输入“London”，sheet 中的 DetailView 将完全空白。如果我随后输入“Rome”作为下一个条目，sheet 中的 DetailView 会显示上一个“London”条目的天气信息。在文本字段中输入“巴黎”会显示“罗马”的天气信息，依此类推...

总而言之，在我将整个文本字段和按钮功能移动到单独的视图后，sheet 中的 ForEach 方法停止正常工作。知道我描述的问题为什么会发生吗？

这是我的代码：

内容视图

struct ContentView: View {
    // Whenever something in the viewmodel changes, the content view will know to update the UI related elements
    @StateObject var viewModel = WeatherViewModel()
        
    var body: some View {
        NavigationView {
            VStack(alignment: .leading) {
                List {
                    ForEach(viewModel.cityNameList.reversed()) { city in
                        NavigationLink(destination: DetailView(detail: city), label: {
                            Text(city.name).font(.system(size: 18))
                            Spacer()
                            Text("\(city.main.temp, specifier: "%.0f")&deg;")
                                .font(.system(size: 18))
                        })
                    }
                    .onDelete { indexSet in
                        let reversed = Array(viewModel.cityNameList.reversed())
                        let items = Set(indexSet.map { reversed[[=10=]].id })
                        viewModel.cityNameList.removeAll { items.contains([=10=].id) }
                    }
                }
                .refreshable {
                    viewModel.updatedAll()
                }
                
                TextFieldView(viewModel: viewModel)
                
            }.navigationBarTitle("Weather", displayMode: .inline)
        }
    }
}
struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}

TextFieldView

struct TextFieldView: View {
    
    @State private var cityName = ""
    @State private var showingDetail = false
    @FocusState var isInputActive: Bool
    
    var viewModel: WeatherViewModel
    
    var body: some View {
        HStack {
            TextField("Enter City Name", text: $cityName)
                .focused($isInputActive)
            Spacer()
            .toolbar {
                ToolbarItemGroup(placement: .keyboard) {
                    Button("Done") {
                        isInputActive = false
                    }
                }
            }
            if isInputActive == false {
                Button(action: {
                    viewModel.fetchWeather(for: cityName)
                    cityName = ""
                    self.showingDetail.toggle()
                }) {
                    Image(systemName: "plus")
                        .font(.largeTitle)
                        .frame(width: 75, height: 75)
                        .foregroundColor(Color.white)
                        .background(Color(.systemBlue))
                        .clipShape(Circle())
                }
                .sheet(isPresented: $showingDetail) {
                    ForEach(0..<viewModel.cityNameList.count, id: \.self) { city in
                        if (city == viewModel.cityNameList.count-1) {
                            DetailView(detail: viewModel.cityNameList[city])
                        }
                    }
                }
            }
        }
        .frame(minWidth: 100, idealWidth: 150, maxWidth: 500, minHeight: 30, idealHeight: 40, maxHeight: 50, alignment: .leading)
            .padding(.leading, 16)
            .padding(.trailing, 16)
    }
}

struct TextFieldView_Previews: PreviewProvider {
    static var previews: some View {
        TextFieldView(viewModel: WeatherViewModel())
    }
}

详细视图

struct DetailView: View {
    
    @State private var cityName = ""
    @State var selection: Int? = nil
    
    var detail: WeatherModel
        
    var body: some View {
        VStack(spacing: 20) {
            Text(detail.name)
                .font(.system(size: 32))
            Text("\(detail.main.temp, specifier: "%.0f")&deg;")
                .font(.system(size: 44))
            Text(detail.firstWeatherInfo())
                .font(.system(size: 24))
        }
    }
}

struct DetailView_Previews: PreviewProvider {
    static var previews: some View {
        DetailView(detail: WeatherModel.init())
    }
}

视图模型

class WeatherViewModel: ObservableObject {
    
    @Published var cityNameList = [WeatherModel]()

    func fetchWeather(for cityName: String) {
        guard let url = URL(string: "https://api.openweathermap.org/data/2.5/weather?q=\(cityName.escaped())&units=imperial&appid=<YourAPIKey>") else { return }

        let task = URLSession.shared.dataTask(with: url) { data, _, error in
            guard let data = data, error == nil else { return }
            do {
                let model = try JSONDecoder().decode(WeatherModel.self, from: data)
                DispatchQueue.main.async {
                    self.addToList(model)
                }
            }
            catch {
                print(error)
            }
        }
        task.resume()
    }
        
    func updatedAll() {
        // keep a copy of all the cities names
        let listOfNames = cityNameList.map{[=13=].name}
        // fetch the up-to-date weather info
        for city in listOfNames {
            fetchWeather(for: city)
        }
    }
    
    func addToList( _ city: WeatherModel) {
        // if already have this city, just update
        if let ndx = cityNameList.firstIndex(where: {[=13=].name == city.name}) {
            cityNameList[ndx].main = city.main
            cityNameList[ndx].weather = city.weather
        } else {
            // add a new city
            cityNameList.append(city)
        }
    }
}

型号

struct WeatherModel: Identifiable, Codable {
    let id = UUID()
    var name: String = ""
    var main: CurrentWeather = CurrentWeather()
    var weather: [WeatherInfo] = []
    
    func firstWeatherInfo() -> String {
        return weather.count > 0 ? weather[0].description : ""
    }
}

struct CurrentWeather: Codable {
    var temp: Double = 0.0
    var humidity = 0
}

struct WeatherInfo: Codable {
    var description: String = ""
}

Answer 1

您需要在 TextFieldView 中使用 ObservedObject 才能使用您的您在 ContentView 中创建的原始（单一真实来源）@StateObject var viewModel 并观察对其的任何更改。

所以使用这个：

struct TextFieldView: View {
    @ObservedObject var viewModel: WeatherViewModel
    ...
}

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