多控制器管理 UITabBarController,跟UINavigationController类似,UITabBarController也可以轻松管理多个控制器,轻松完成控制器之间的切换,例如QQ,微信.

头文件定义：

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@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

 UITabBarController通过UITabBar *tabBar管理UITabBarItem, UITabBar默认高度49

　　ios6以前控制器的高度是：屏幕的高低-状态栏高度-tabBar高度 ,ios7以后控制器的高度是屏幕的高度

UITabBar切换原理:tab切换获取控制器上的view,把view添加到屏幕上,屏幕上之前的view移开 并不会销毁,可以重复来回切换, 只有控制器销毁或内存警告时view才有可能消失.

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- ( 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 ; }

 

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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;

 

1	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

 

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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;

 

被管理的控制器访问UITabBarController和tabBarItem,通过被管理的控制器去设置tabBarItem相应属性值

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@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

 

 控制器view也是懒加载机制,用到时才创建显示

view生命周期：

UITabBarController管理的控制器,往回切换控制器中的view并不会销毁,这点跟导航控制器有区别(导航控制器返回时之前的显示的view会销毁)

 

app主流UI框架结构