UINavigationController 是IOS中规定多视图控制器,本身也是试图控制器,也自带一个试图,根视图上方携带有navigtionBar(导航条)
initWithRootViewController
初始化时指定一个导航控制器的根视图控制器
导航控制器管理多个视图控制器的方式:原理:以栈的形式管理,当push时视图控制器进栈, 当POP时视图控制器出栈,视图控制器对象空间回收,屏幕上永远显示的是栈顶元素的根视图
//视图将要出现
- (void)viewWillAppear:(BOOL)animated {    [superviewWillAppear:animated];   NSLog(@"%s %d",__FUNCTION__, __LINE__); }
//视图已经出现 - (void)viewDidAppear:(BOOL)animated {    [superviewDidAppear:animated];   NSLog(@"%s %d",__FUNCTION__, __LINE__); }
视图将要消失 -(void)viewWillDisappear:(BOOL)animated {    [superviewWillDisappear:animated];   NSLog(@"%s %d",__FUNCTION__, __LINE__); }
//视图已经消失 -(void)viewDidDisappear:(BOOL)animated {    [superviewDidDisappear:animated];   NSLog(@"%s %d",__FUNCTION__, __LINE__); }
视图的显示与消失   视图从a进入到b时,a-viewwillDisappear--->b-viewDidDisappear--->B-viewDidAppear   当从b返回到a时 b-viewWillDisappear--->a-viewWillAppear--->B-viewDidDisappear--->a-viewDisAppear

UINavigationController多视图控制器