BasicViewController : UIViewController SecondViewController : UIViewController ThirdViewController : UIViewController
然后我们在BasicViewController .m文件中push一个viewController：
SecondViewController *svc = [SecondViewController new];
[self.navigationController pushViewController:svc animated:true];
在SecondViewController.m文件中pop出viewController：
[self.navigationController popViewControllerAnimated:true]
问题就来了，
push和pop是同一个viewController，那为什么用self.navigationController 就可以知道了
其中在AppDelegate.m：
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
// Override point for customization after application launch.
BasicViewController *basicViewController = [BasicViewController new];//实例化内存后，_parentViewController-->nil
UINavigationController *navigationController = [[UINavigationController alloc] initWithRootViewController:basicViewController];
// self.window.rootViewController = basicViewController.parentViewController;
self.window.rootViewController = navigationController;
[self.window makeKeyAndVisible];
return YES;
}
等价于
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
// Override point for customization after application launch.
BasicViewController *basicViewController = [BasicViewController new];//实例化内存后，_parentViewController-->nil
UINavigationController *navigationController = [[UINavigationController alloc] initWithRootViewController:basicViewController];
self.window.rootViewController = basicViewController.parentViewController; //不可以注释上一句，因为上一句是为_parentViewController实例化
// self.window.rootViewController = navigationController;
[self.window makeKeyAndVisible];
return YES;
}
分配内存如图
