檢查UIViewController是否有一個特定的變量

Question

如何檢查ViewController是否有指定的變量？

@objc protocol InsetBlurModalSequeProtocol { 
    func getBackgroundImage() -> UIImage 
} 



@objc(InsetBlurModalSeque) class InsetBlurModalSeque: UIStoryboardSegue { 

    override func perform() { 
     var sourceViewController = self.sourceViewController as UIViewController 
     let destinationViewController = self.destinationViewController as UIViewController 

     // Make sure the background is ransparent 
     destinationViewController.view.backgroundColor = UIColor.clearColor() 

     var image:UIImage? 
     if sourceViewController is InsetBlurModalSequeProtocol { 
      // Use secial background plate 
      image = InsetBlurModalSequeProtocol(sourceViewController).getBackgroundImage() // Error 'InsetBlurModalSequeProtocol' is not constructible with '@lvalue UIViewController' 
     } 
     else { 
      // Take screenshot from source VC 
      UIGraphicsBeginImageContext(sourceViewController.view.bounds.size) 
      sourceViewController.view.drawViewHierarchyInRect(sourceViewController.view.frame, afterScreenUpdates:true) 
      image = UIGraphicsGetImageFromCurrentImageContext() 
      UIGraphicsEndImageContext() 
     } 

Answer 1

您不能檢查，如果一個對象具有一定的成員變量，只有當它可以轉換爲某種類型。一旦你知道它可以被轉換成某種類型，你肯定知道它是否有一個成員變量。

你可以做一個可選的鑄像這樣：

if let specialVc = vc as? SpecialViewController { 
    // use specialVc.specialVar 
} 
else { 
    // the view controller could not be cast so it does not have specialVar 
} 

你也可以，如果你喜歡的是在一個完整的類上使用的協議。