多控制器管理 UITabBarController

@interface UITabBarController : UIViewController <UITabBarDelegate, NSCoding>

@property(nonatomic,copy) NSArray *viewControllers;
// If the number of view controllers is greater than the number displayable by a tab bar, a "More" navigation controller will automatically be shown.
// The "More" navigation controller will not be returned by -viewControllers, but it may be returned by -selectedViewController.
- (void)setViewControllers:(NSArray *)viewControllers animated:(BOOL)animated;

@property(nonatomic,assign) UIViewController *selectedViewController; // This may return the "More" navigation controller if it exists.
@property(nonatomic) NSUInteger selectedIndex;

@property(nonatomic,readonly) UINavigationController *moreNavigationController; // Returns the "More" navigation controller, creating it if it does not already exist.
@property(nonatomic,copy) NSArray *customizableViewControllers; // If non-nil, then the "More" view will include an "Edit" button that displays customization UI for the specified controllers. By default, all view controllers are customizable.

@property(nonatomic,readonly) UITabBar *tabBar NS_AVAILABLE_IOS(3_0); // Provided for -[UIActionSheet showFromTabBar:]. Attempting to modify the contents of the tab bar directly will throw an exception.

@property(nonatomic,assign) id<UITabBarControllerDelegate> delegate;

@end

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    NSLog(@"%s",__func__);
    // Override point for customization after application launch.
    self.window = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds];
    
    UITabBarController *tabBarVc = [[UITabBarController alloc] init];
    
    UIViewController *vc1 = [[UIViewController alloc] init];
    vc1.view.backgroundColor = [UIColor redColor];
    UITabBarItem *barItem1 = vc1.tabBarItem;
    barItem1.title = @"消息";
    [tabBarVc addChildViewController:vc1];
    
    
    UIViewController *vc2 = [[UIViewController alloc] init];
    vc2.view.backgroundColor = [UIColor greenColor];
    UITabBarItem *barItem2 = vc2.tabBarItem;
    barItem2.title = @"好友";
    [tabBarVc addChildViewController:vc2];
    
    
    UIViewController *vc3 = [[UIViewController alloc] init];
    vc3.view.backgroundColor = [UIColor blueColor];
    UITabBarItem *barItem3 = vc3.tabBarItem;
    barItem3.title = @"动态";
    [tabBarVc addChildViewController:vc3];
    
    
    self.window.rootViewController = tabBarVc;
    
    [self.window makeKeyAndVisible];
    
    return YES;
}

UITabBarController添加控制器的方式有2种
添加单个子控制器
- (void)addChildViewController:(UIViewController *)childController;

设置子控制器数组
@property(nonatomic,copy) NSArray *viewControllers;

如果UITabBarController有N个子控制器，那么UITabBar内部就会有N个UITabBarButton作为子控件

UITabBarButton里面显示什么内容，由对应子控制器的tabBarItem属性决定

UITabBarItem有以下属性影响着UITabBarButton的内容
标题文字
@property(nonatomic,copy) NSString *title;

图标
@property(nonatomic,retain) UIImage *image;

选中时的图标
@property(nonatomic,retain) UIImage *selectedImage;

提醒数字
@property(nonatomic,copy) NSString *badgeValue;

@interface UIViewController (UITabBarControllerItem)

@property(nonatomic,retain) UITabBarItem *tabBarItem; // Automatically created lazily with the view controller‘s title if it‘s not set explicitly.

@property(nonatomic,readonly,retain) UITabBarController *tabBarController; // If the view controller has a tab bar controller as its ancestor, return it. Returns nil otherwise.

@end