UITabBarController是選項卡欄導航控制器，顯示效果是在頁面底部有多個選項卡，通過點擊不同選項卡可以在不同的ViewController之間進行切換。
這種對象的層次結構至少包含6個對象：
一個UITabBarController；
兩個UIViewController；
一個UITabBar；
兩個UITabBarItem；
UITabBarController
是選項卡欄視圖控制器，UITabBar是底部兩個UITabBarItem的容器，管理兩個UITabBarItem，每個UITabBarItem對
應一個UIViewController，然后每個UIViewController都有自己的視圖和視圖控制器。
UITabBarController中有一個viewControllers屬性，這是一個NSArray，包含選項卡控制器的視圖控制器
下面來用代碼創建一個UITabBarController：
下面是工程結構：
首先創建兩個帶xib文件的ViewController，分別為FirstViewController和SecondViewController
然后在AppDelegate.h中聲明@property (strong,nonatomic)
UITabBarController *tabBarController;，并添加協議UITabBarControllerDelegate
在.m中實現如下代碼：
- - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
- {
- self.window = [[[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]] autorelease];
-
-
-
- FirstViewController *firstViewController = [[FirstViewController alloc]init];
-
-
- firstViewController.title = @"First view";
-
- UITabBarItem *firstItem = [[UITabBarItem alloc]initWithTitle:@"First" image:nil tag:1];
- [firstItem setFinishedSelectedImage:[UIImage imageNamed:@"p1"] withFinishedUnselectedImage:[UIImage imageNamed:@"p1_f"]];
- firstViewController.tabBarItem = firstItem;
-
-
- SecondViewController *secondViewController = [[SecondViewController alloc]init];
-
-
- UITabBarItem *secondItem = [[UITabBarItem alloc]initWithTitle:@"Second" image:nil tag:2];
-
-
- [secondItem setFinishedSelectedImage:[UIImage imageNamed:@"p2_f"] withFinishedUnselectedImage:[UIImage imageNamed:@"p2"]];
-
- [secondItem setBadgeValue:@"2"];
-
- secondViewController.tabBarItem = secondItem;
- [secondItem release];
-
-
- self.tabBarController = [[[UITabBarController alloc]init] autorelease];
- self.tabBarController.delegate = self;
-
-
- self.tabBarController.viewControllers = [NSArray arrayWithObjects:firstViewController,secondViewController, nil];
-
- [firstViewController release];
- [secondViewController release];
-
-
-
-
-
- self.window.rootViewController = self.tabBarController;
-
- self.window.backgroundColor = [UIColor whiteColor];
- [self.window makeKeyAndVisible];
- return YES;
- }
