UITabBarController初学

RViewController1 *vc1 = [[RViewController1 alloc]init];        UINavigationController *navController = [[UINavigationController alloc]initWithRootViewController:vc1];    //只赋值 tabBarItem.title, 通过.title属性取值是取不到值    //navController.tabBarItem.title = @"Page 1";        //相当于对tabBarItem.title  和 navigationItem.title同时赋值    navController.title = @"Page 1";    navController.tabBarItem.image = [UIImage imageNamed:@"1.jpg"];        RViewController2 *vc2 = [[RViewController2 alloc]init];    vc2.title =@"Page 2";//    UITabBarItem *item2 = [[UITabBarItem alloc]initWithTitle:@"Page 2" image:[UIImage imageNamed:@"2.png" ] selectedImage:[UIImage imageNamed:@"2_PRessed.png"]];    vc2.tabBarItem.image = [UIImage imageNamed:@"2.png"];        RViewController3 *vc3 = [[RViewController3 alloc]init];    vc3.title =@"Page 3";    vc3.tabBarItem.image = [UIImage imageNamed:@"3.png"];        RViewController4 *vc4 = [[RViewController4 alloc]init];    vc4.title =@"Page 4";    vc4.tabBarItem.image = [UIImage imageNamed:@"4.png"];    vc4.tabBarItem.badgeValue = @"10";        RViewController5 *vc5 = [[RViewController5 alloc]init];        //创建 UITabItem的实例    UITabBarItem *item1 = [[UITabBarItem alloc]initWithTabBarSystemItem:UITabBarSystemItemHistory tag:0];    vc5.tabBarItem = item1;        NSArray *controllers = [NSArray arrayWithObjects:navController,vc2,vc3,vc4, nil];        UITabBarController *tabController = [[UITabBarController alloc]init];    tabController.viewControllers = controllers;        self.window.rootViewController = tabController;