SwiftUI ContentView_Previews不运行函数

Question

我试图用直接用ContentView_Previews编写的方法为我的Xcode预览生成一些模拟数据，但我没有成功，我也不明白为什么。

struct ContentView_Previews: PreviewProvider {
    static let healthManager = generateMockData()
    
    static var previews: some View {
        MainView().environmentObject(healthManager)
    }
    
    static func generateMockData() -> HealthManager {
        let defaultHealthManager = HealthManager()
        defaultHealthManager.gavePermissions = true
        
        for i in 1...10 {
            let defaultWorkout = HKWorkout(activityType: .traditionalStrengthTraining,
                                           start: .now - Double(i * 50),
                                           end: .now,
                                           duration: Double(i * 100),
                                           totalEnergyBurned: HKQuantity(unit: .largeCalorie(), doubleValue: Double(i * 100)),
                                           totalDistance: nil,
                                           device: nil,
                                           metadata: nil)
            
            defaultHealthManager.previousWorkouts.append(defaultWorkout)
        }
        
        
        return defaultHealthManager
    }
}

基本上，它显示的是defaultHealthManager对象除了默认值之外没有设置的值。如果我在运行时在实际视图中为我的属性调用ContentView_Previews. generateMockData()，它可以正常工作。

Answer 1

有时，我似乎需要创建一个我所说的中间视图来使事情正常工作。像这样有用吗？

struct MainViewIntermediary: View {
    @State var healthManager: HealthManager

    init() {
        let defaultHealthManager = HealthManager()
        defaultHealthManager.gavePermissions = true
        
        for i in 1...10 {
            let defaultWorkout = HKWorkout(activityType: .traditionalStrengthTraining,
                                           start: .now - Double(i * 50),
                                           end: .now,
                                           duration: Double(i * 100),
                                           totalEnergyBurned: HKQuantity(unit: .largeCalorie(), doubleValue: Double(i * 100)),
                                           totalDistance: nil,
                                           device: nil,
                                           metadata: nil)
            
            defaultHealthManager.previousWorkouts.append(defaultWorkout)
            _healthManager = State(initialValue: defaultHealthManager)
        }
    }

   var body: some View {
        MainView().environmentObject(healthManager)
    }
}

然后预览提供程序变成：

struct ContentView_Previews: PreviewProvider {
    
    static var previews: some View {
        MainViewIntermediary()
    }
}