我有一个scrollView，其中包含动态数量的WeatherViewController，每个WeatherViewController显示用户已保存的不同城市的天气数据。用户可以从WeatherViewControllers筛选到CityListViewController。他们可以在其中从列表中添加和删除城市，而在解散CityListViewController后又应从scrollView中添加和删除WeatherViewControllers，这就是我遇到的问题。

目前，我正在尝试使用协议调用func reloadScrollView，该函数在关闭（viewDidDisappear）CityListViewController后在scrollViewController中调用viewDidLoad，但出现错误：

Fatal error: Unexpectedly found nil while unwrapping an Optional value: file

何时到达：

totalScrollView.addSubview(weatherScreen.view)

使用调试器，我发现totalScrollView为nil，这导致了问题。有没有一种方法可以使scrollView加载，因此在关闭另一个viewController时它不会为

OR

使用该协议调用此函数的更好时机吗？

侧面注意：最初打开该应用程序时，scrollView会正确加载，并且UIScrollView中的所有正确WeatherWeatherController以及列表中正确的城市。

class ScrollViewController: UIViewController,ScrollReloadProtocol {

func reloadScrollView() {

    print("SCROLL RELOADED!!!!!*******")
    self.viewDidLoad()
}

@IBOutlet var totalScrollView: UIScrollView!
var pages = [ViewController]()
var x = 0
var weatherScreensArray = [SavedCityEntity]()
var weatherScreenStringArray = [String]()
let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
var horizString = "H:|[page1(==view)]"

let defaults = UserDefaults.standard


override func viewDidLoad() {
    super.viewDidLoad()

    //userDefaults used to keep track of which screen is which to put different cities on different viewControllers
    defaults.set(0,forKey: "screenNumber")
    //load cities to get number of cities saved
    loadCities()

    var views : [String: UIView] = ["view": view]
    //create all weatherWeatherControllers
    while x <= weatherScreensArray.count {

        pages.append(createAndAddWeatherScreen(number: x))
        weatherScreenStringArray.append("page\(x+1)")
        views["\(weatherScreenStringArray[x])"] = pages[x].view
        let addToHoriz = "[\(weatherScreenStringArray[x])(==view)]"
        horizString.append(addToHoriz)

        x+=1
    }

    horizString.append("|")

    let verticalConstraints = NSLayoutConstraint.constraints(withVisualFormat: "V:|[page1(==view)]|",options: [],metrics: nil,views: views)
    let horizontalConstraints = NSLayoutConstraint.constraints(withVisualFormat: horizString,options: [.alignAllTop,.alignAllBottom],views: views)

    NSLayoutConstraint.activate(verticalConstraints + horizontalConstraints)
}

//Function to create and add weatherViewController
func createAndAddWeatherScreen(number: Int) -> ViewController {

        defaults.set(number,forKey: "screenNumber")

      let story = uistoryboard(name: "Main",bundle: nil)
        let weatherScreen = story.instantiateViewController(identifier: "View Controller") as! ViewController


        weatherScreen.view.translatesAutoresizingMaskintoConstraints = false

        totalScrollView.addSubview(weatherScreen.view)

        addChild(weatherScreen)
        weatherScreen.didmove(toParent: self)

    return weatherScreen
}

}