不能在 swift 中使用 for...in 或 forEach 循环来快速打印视图

Question

所以这就是问题所在。当我在文件中给出值时，我的代码运行良好。但是，我制作了一个单独的模型文件，我想从中迭代 WeatherDay 对象数组以打印它们以使它们动态化。但是，从逻辑上讲，这听起来很容易，但我遇到了这些烦人的错误，这些错误不会让我编译。任何人帮助！代码如下：

struct ContentView: View {
    
    @State private var isNight = false
    
    var body: some View {
        ZStack {
            var selectedWeather = getWeatherValues()
            // binding basically enforces that the value for the object stays the same
            BackgroundView(isNight: $isNight)
            
            VStack {
                let days = selectedWeather.getWeatherDayListData()
                CityTextView(cityName: selectedWeather.getCity())
                
//                first object
                mainWeatherView(isNight: $isNight, todayWeather:
                                    selectedWeather.getWeatherDayListData()[0])

                HStack(spacing: 20) {
                    weatherDayView(weatherDays: selectedWeather.getWeatherDayListData())

                }
                
                
            }
            Spacer() //basically used to move the text to the top of the frame
            Button {
                isNight.toggle()
            } label: {
                WeatherButton(title: "Change Day Time",
                              textColor: .blue,
                              backgroundColor: .white)
                
            }
            Spacer()
        }
    }
}

struct weatherDayView: View {
    //this is where i get all the errors like
    //closure expression is unused
    //expected { in struct
    //expressions are not allowed at the top level.
    
    @State var weatherDays: [WeatherDay]
    
    var body: some View {
        ForEach(weatherDays, id: \.self) { singleDay in
            
            VStack {
                Text(singleDay.dayOfWeek)
                    .font(.system(size: 18, weight: .medium, design: .default))
                    .foregroundColor(.white)
                Image(systemName: singleDay.ImageName)
                    .renderingMode(.original)
                    .resizable()
                    .aspectRatio(contentMode: .fit)
                    .frame(width: 40, height: 40)
                Text("\(singleDay.temperature)°")
                    .font(.system(size: 28, weight: .medium))
                    .foregroundColor(.white)
            }
        }
    }
}

Answer 1

这里有很多错误，从您的ForEach 开始。 ForEach 不是 for...in，尽管它们有类似的目的：循环访问随机访问集合。 ``for...inis used outside of a view, andForEach` 在视图中使用，并为每个元素创建一个视图。

接下来，你不能像函数一样声明结构。参数进入结构声明内部。之后，这是一个处理视图层次结构的案例，以确保所有内容都具有正确的Type。我已经修复了你的代码，所以你有一个例子，尽管你绝对可以大大收紧你的代码。我强烈建议通过Apple's SwiftUI Tutorials 和Stanford's CS193P course，因为这些是基本的 SwiftUI 问题。

另外，发布Minimal, Reproducible Example 时要小心。您应该制作一个新的应用程序并确保它可以编译。在本例中，您省略了 WeatherButton() 视图，因此它并不重要，但有时确实如此。

还有一个简短的说明，通常您不需要在 StackOverflow 中发布您的import，而当您import SwiftUI 时，您会得到由SwiftUI 导入的Foundation，因此您不需要同时导入两者。

struct ContentView: View {
    @State private var isNight = false
    
    var body: some View {
        ZStack {
            // binding basically enforces that the value for the object stays the same
            BackgroundView(isNight: $isNight)
            VStack {
                let selectedWeather = getWeatherValues()
                
                CityTextView(cityName: selectedWeather.getCity())
                mainWeatherView(isNight: $isNight, temperature: 76)
                
                HStack(spacing: 20) {
                    weatherDayView(weatherDays: selectedWeather.getWeatherDayListData())
                }
                
                
                
            }
            Spacer() //basically used to move the text to the top of the frame
            Button {
                isNight.toggle()
            } label: {
                WeatherButton(title: "Change Day Time",
                              textColor: .blue,
                              backgroundColor: .white)
                
            }
            Spacer()
        }
        
    }
}


struct weatherDayView: View {
//this is where i get all the errors like
//closure expression is unused
//expected { in struct
//expressions are not allowed at the top level.
        
    @State var weatherDays: [WeatherDay]
    
        var body: some View {
            ForEach(weatherDays, id: \.self) { singleDay in

            VStack {
                Text(singleDay.dayOfWeek)
                    .font(.system(size: 18, weight: .medium, design: .default))
                    .foregroundColor(.white)
                Image(systemName: singleDay.ImageName)
                    .renderingMode(.original)
                    .resizable()
                    .aspectRatio(contentMode: .fit)
                    .frame(width: 40, height: 40)
                Text("\(singleDay.temperature)°")
                    .font(.system(size: 28, weight: .medium))
                    .foregroundColor(.white)
            }
        }
    }
}

编辑：

添加WeatherDay符合Hashable。

struct WeatherDay: Hashable {
    var dayOfWeek: String
    var ImageName: String
    var temperature: Int
    
    init(dayOfWeek: String, ImageName: String, temperature: Int)
    {
        self.dayOfWeek = dayOfWeek
        self.ImageName = ImageName
        self.temperature = temperature
        
    }
}