Ios 弹出到导航堆栈中的特定viewcontroller

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;

---

这里到底发生了什么事。我认为这里没有创建MyGroupViewController的新实例。

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类型（但始终从UIViewController继承），因此使用通用UIViewController。但是，编译器不知道该视图控制器是什么类型，因此它被强制转换为MyGroupViewController。发生这种情况时，编译器知道类的类型，您可以向它发送仅适用于该类的消息

在这种情况下，这是不必要的，因为可以简化为：

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

简短回答：它将变量类型更改为括号中指定的类型，以避免编译器警告。

for（int m=0；m
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];   
  }   
} 

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)
  }
}

论斯威夫特

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
我当前的类中没有viewcontroller实例。@jean-Paul Scott您已经在快速枚举中创建了UIViewController实例，或者您可以说foreach循环
MyGroupViewController*groupViewController=（MyGroupViewController*）viewController；
我想知道这段代码中发生了什么。这个groupViewController是导航堆栈中的同一个实例吗？我想你没有回答我的问题。这一行将引用所需的view controller“此处viewController是MyGroupViewController的UIViewController基类的引用，但viewController持有MyGroupViewController对象，因此我们可以在此处键入cast”。这正是我所要查找的。因此使用了与导航堆栈中已存在的MyGroupViewController相同的实例。对吗？
- (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;
        }
    }

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