膨化到特定的ViewController在導航堆棧

我有一個遇到的一段代碼彈出到特定的ViewController在導航堆棧如下膨化到特定的ViewController在導航堆棧

for (UIViewController* viewController in self.navigationController.viewControllers) { 
    if ([viewController isKindOfClass:[MyGroupViewController class]]) { 
     MyGroupViewController *groupViewController = (MyGroupViewController*)viewController; 
     [self.navigationController popToViewController:groupViewController animated:YES]; 
    } 
}

目的是彈出到MyGroupViewController。但我不理解這行代碼。

MyGroupViewController *groupViewController = (MyGroupViewController*)viewController;

這裏到底發生了什麼。我不認爲在這裏創建了MyGroupViewController的新實例。

來源

2012-06-14 Jean Paul Scott

//This for loop iterates through all the view controllers in navigation stack. 
for (UIViewController* viewController in self.navigationController.viewControllers) { 

    //This if condition checks whether the viewController's class is MyGroupViewController 
    // if true that means its the MyGroupViewController (which has been pushed at some point) 
    if ([viewController isKindOfClass:[MyGroupViewController class]]) { 

     // Here viewController is a reference of UIViewController base class of MyGroupViewController 
     // but viewController holds MyGroupViewController object so we can type cast it here 
     MyGroupViewController *groupViewController = (MyGroupViewController*)viewController; 
     [self.navigationController popToViewController:groupViewController animated:YES]; 
    } 
}

你也可以像這樣

if ([viewController isKindOfClass:[MyGroupViewController class]]) { 
      [self.navigationController popToViewController:viewController animated:YES]; 
}

斯威夫特代碼

//Itrate through all the view controllers in navigation stack 
for vc in self.navigationController!.viewControllers { 
    // Check if the view controller is of MyGroupViewController type 
    if let myGropupVC = vc as? MyGroupViewController { 
    self.navigationController?.popToViewController(myGropupVC, animated: true) 
    } 
}

來源

2012-06-14 05:25:29

「這裏viewController是MyGroupViewController的基類UWiewController的引用，但viewController保存MyGroupViewController對象，因此我們可以在此處鍵入轉換它」。這正是我正在尋找的。因此，使用了已經在導航堆棧中的同一個MyGroupViewController實例。對？ –

是的，它與之前推送的實例相同。 –

正在枚舉導航控制器堆棧的視圖控制器。由於這些視圖控制器可以是任何類型的（但總是從UIViewController繼承），所以使用了通用的UIViewController。但是，編譯器不會知道該視圖控制器是什麼類型，因此它將被轉換爲MyGroupViewController。當發生這種情況時，編譯器知道類的類型，並且可以發送只適用於該類的消息。

在這種情況下，它是一種不需要的，因爲它可以簡化爲這樣：

(UIViewController* viewController in self.navigationController.viewControllers) { 
    if ([viewController isKindOfClass:[MyGroupViewController class]]) { 
     [self.navigationController popToViewController:viewController animated:YES]; 
    } 
}

簡短的回答：它改變一個變量類型在括號中指定，以避免編譯器警告類型。

來源

2012-06-14 05:00:27

我沒有這個視圖 - 控制實例在我目前的類。 –

@jean Paul Scott你已經在快速枚舉中創建了UIViewController的一個實例，或者你可以說foreach循環 –

'MyGroupViewController * groupViewController =（MyGroupViewController *）viewController;'我想知道在這段代碼中會發生什麼。這個groupViewController是導航堆棧中的同一個實例嗎？ –

for (int m=0; m<[self.navigationController.viewControllers count]; m++) 
{ 

     if([[self.navigationController.viewControllers objectAtIndex:m] isKindOfClass:[MyGroupViewController class]]) 
      { 

       MyGroupViewController * groupViewController = [self.navigationController.viewControllers objectAtIndex:m]; 
       [self.navigationController popToViewController:groupViewController animated:YES]; 
      } 
}

來源

2012-06-14 05:09:22

我不認爲你回答我的問題。 –

該行將提供所需的視圖控制器的引用 –

- (void) RetunToSpecificViewController{ 

    for (UIViewController *controller in self.navigationController.viewControllers) { 
     if ([controller isKindOfClass:[AnOldViewController class]]) { 
     //Do not forget to import AnOldViewController.h 

      [self.navigationController popToViewController:controller 
               animated:YES]; 
      break; 
     } 
    }

斯威夫特

func RetunToSpecificViewController() 
{ 
    let viewControllers: [UIViewController] = self.navigationController!.viewControllers as [UIViewController] 
    self.navigationController!.popToViewController(viewControllers[viewControllers.count 
     - 5], animated: true) 
}

我們寫一個更好的教程，你可以檢查 https://appengineer.in/2014/03/13/pop-to-specific-view-controller-in-ios/

來源

2015-04-28 07:45:04

膨化到特定的ViewController在導航堆棧

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