Swift 4，必须仅从主线程使用警告 [英] Swift 4 ,must be used from main thread only warning

问题描述

当我在 Xcode 9 中使用 Swift4 给我

When I using Swift4in Xcode 9 gives me

UIApplication.delegate 只能在主线程中使用

UIApplication.delegate must be used from main thread only

.... 只能在主线程中使用

.... must be used from main thread only

从后台线程组调用的UI API

UI API called from background thread Group

紫色警告.

我的代码；

var appDelegate = UIApplication.shared.delegate as! AppDelegate
public var context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
let prefs:UserDefaults = UserDefaults.standard
var deviceUUID = UIDevice.current.identifierForVendor!.uuidString

警告行是;

  public var context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext

另一个这样的警告；

 let parameters = [
                        "tel": "\(self.phone.text!)"
                        ] as [String : String]

给予

UITextField.text 只能在主线程中使用

UITextField.text must be used from main thread only

又是同样的错误..

我该如何解决?有什么想法吗?

How can I fix it ? Any idea ?

推荐答案

您正在后台队列上进行此调用.要修复，请尝试类似……

You're making this call on a background queue. To fix, try something like…

public var context: NSManagedObjectContext

DispatchQueue.main.async {

    var appDelegate = UIApplication.shared.delegate as! AppDelegate
    context = appDelegate.persistentContainer.viewContext        
}

尽管这是一种非常糟糕的方法……但您将 App Delegate 用作全局变量(我们都知道这很糟糕！)

Although this is a pretty bad way to do this… you're using your App Delegate as a global variable (which we all know is bad!)

您应该考虑将托管对象上下文从视图控制器传递到视图控制器......

You should look at passing the managed object context from view controller to view controller…

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: 

    (window?.rootViewController as? MyViewController)?.moc = persistentContainer.viewContext
}

等等

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