弹出到导航堆栈中的特定viewcontroller

Question

我遇到了一段代码,可以弹出到导航堆栈中的特定viewcontroller,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];
    }
}

目标是弹出到MyGroupViewController.但我不理解这行代码.

MyGroupViewController *groupViewController = (MyGroupViewController*)viewController;

什么事发生在这里.我不认为这里创建了一个新的MyGroupViewController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];
 }

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)
  }
}