Swift 4 , must be used from main thread only 警告

Question

当我在 Xcode 9 中使用 Swift4 时，我得到

UIApplication.delegate must be used from main thread only

.... must be used from main thread only

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

警告线是；

  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 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？

Answer 1

您正在后台队列中进行此调用。要修复，请尝试类似...

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……您将 App Delegate 用作全局变量（我们都知道这很糟糕！）

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……

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: 

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

等等

Swift 4 , must be used from main thread only 警告

Swift 4 ,must be used from main thread only warning

appdelegate

swift4

xcode9