用继承自UINavigationController与UITabbarController 创建类，将前者设置为RootViewController,出现了一个问题，navigetionController的title不显示，在controller里面怎么设置都不显示，原因是这个样子的：
title这个属性实际上是属于UIViewController而不属于UINavigationController。所以，这个属性是从UIViewController上面继承过来的。而不是UINavigationController上面的名字。由于UINavigationController属于容器，所以最少需要一个RootController。然后在RootController的viewDidLoad设置title而不是在UINavigationController的subclass中设置。而且viewDidLoad设置的title是统一显示的，导航视图控制的UIViewController的title都是一样的，我的解决方法是：将逻辑更换，UITabbarController设置为RootViewController，
1 -(void)addTage:(Class)controller addName:(NSString *)name addImage:(NSString *)image addSelectImage:(NSString *)selectImage 2 3 { 4 5 6 7 UIViewController *vc = [[controller alloc] init]; 8 9 UINavigationController *cityNav = [[UINavigationControlleralloc]initWithRootViewController:vc]; 10 11 cityNav.tabBarItem.image = [UIImage imageNamed:image]; 12 13 cityNav.tabBarItem.selectedImage = [UIImage imageNamed:selectImage]; 14 15 cityNav.navigationBar.backgroundColor = [UIColor blueColor]; 16 17 cityNav.tabBarItem.title = name; 18 19 cityNav.navigationBar.barStyle = UIBarStyleDefault; 20 21 cityNav.navigationBar.barTintColor = [UIColor cyanColor]; 22 23 [self.navArray addObject:cityNav]; 24 25 26 27 } 28 29 30 31 self.tabBarController.viewControllers = self.navArray; 32 33 34 self.window.rootViewController = self.tabBarController;
self.navigationItem.title
= @"my title"; sets navigation bar title.
self.tabBarItem.title
= @"my title"; sets tab bar title.
self.title
= @"my title"; sets both of these.