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 -viewWillDisappear：方法不是修改navigationController的视图控制器堆栈的最佳位置，因为它在切换选项卡和在其上按下视图时都会触发。 
 
 我玩了一下这个，发现最好的地方是 - [UITabBarControllerDelegate tabBarController：didSelectViewController：]方法。 所以，首先你需要指定一个对象作为标签栏的委托（我使用了app委托）。 将UITabBarController的delegate属性绑定到在代码或Interface Builder中实现UITabBarControllerDelegate协议的对象。 
 
 然后，实现-tabBarController：didSelectViewController：方法。 现在的诀窍是如何判断何时切换到“地址簿”选项卡。 我使用UINavigationController类型的属性（选项卡的根视图控制器）跟踪相关选项卡的视图控制器。 使用Interface Builder将tab1NavController属性绑定到实际实例后，可以使用它与viewController参数进行比较，以查看刚刚选择的选项卡。 
 
@interface Pop2RootTabSwitchAppDelegate : NSObject 
    <UIApplicationDelegate, UITabBarControllerDelegate> {
  UINavigationController *tab1NavController;
}
@property (nonatomic, retain) IBOutlet UINavigationController *tab1NavController;
@end

@implementation Pop2RootTabSwitchAppDelegate

- (void)tabBarController:(UITabBarController *)tabBarController 
  didSelectViewController:(UIViewController *)viewController {
   NSLog(@"[%@ tabBarController:%@  didSelectViewController:%@]", [self class], 
       tabBarController, viewController);
   if (viewController == tab1NavController) {
       NSLog(@"viewController == tab1NavController");
       [tab1NavController popToRootViewControllerAnimated:NO];
   }
}

The -viewWillDisappear: method is not the best place for modifying the view controller stack for your navigationController because it is triggered both when you switch tabs and when a view is pushed on top of it.
 
I played around with this a bit and found that the best place for this is in the -[UITabBarControllerDelegate tabBarController:didSelectViewController:] method. So, first you need to designate an object to be the delegate for your tab bar (I used the app delegate). Bind the delegate property of your UITabBarController to an object implementing the UITabBarControllerDelegate protocol in code or in Interface Builder.
 
Then, implement the -tabBarController:didSelectViewController: method. The trick now is how to tell when your "address book" tab is being switched to. I kept track of the view controller for the tab in question using a property of type UINavigationController (the root view controller for the tab). After binding the tab1NavController property to the actual instance using Interface Builder, it can be used to compare to the viewController parameter to see what tab was just selected.
 
@interface Pop2RootTabSwitchAppDelegate : NSObject 
    <UIApplicationDelegate, UITabBarControllerDelegate> {
  UINavigationController *tab1NavController;
}
@property (nonatomic, retain) IBOutlet UINavigationController *tab1NavController;
@end

@implementation Pop2RootTabSwitchAppDelegate

- (void)tabBarController:(UITabBarController *)tabBarController 
  didSelectViewController:(UIViewController *)viewController {
   NSLog(@"[%@ tabBarController:%@  didSelectViewController:%@]", [self class], 
       tabBarController, viewController);
   if (viewController == tab1NavController) {
       NSLog(@"viewController == tab1NavController");
       [tab1NavController popToRootViewControllerAnimated:NO];
   }
}