popup到导航堆栈中的特定视图控制器

我碰到一段代码，popup到导航堆栈中的特定视图控制器，如下所示

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

目标是popup到MyGroupViewController。 但我不理解这行代码。

 MyGroupViewController *groupViewController = (MyGroupViewController*)viewController; 

这里到底发生了什么。 我不认为在这里创build一个MyGroupViewController的新实例。

Answer 1

 //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]; } } 

你也可以这样做

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

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SWIFT代码

 //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) } } 

Answer 2

正在枚举导航控制器堆栈的视图控制器。 由于这些视图控制器可以是任何types的（但总是从UIViewControllerinheritance），通用的UIViewController被使用。 但是，编译器将不知道该视图控制器是什么types，所以它正在被铸造到一个MyGroupViewController。 当发生这种情况时，编译器知道什么类的类，你可以发送消息，只适用于该类。

在这种情况下，这是不必要的，因为它可以简化为：

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

简短的回答：它将variablestypes更改为括号中指定的types，以避免编译器警告。

Answer 3

 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]; } } 

Answer 4

 - (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; } } 

在Swift上

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

我们已经写了一个更好的教程，你可以检查https://appengineer.in/2014/03/13/pop-to-specific-view-controller-in-ios/