1.自定义的UITabBarController的释放问题
发生场景：退出登录时候，页面由tabViewController切到登录页，执行代码
@property (strong,nonatomic) GBTabViewController *tabViewController;

LoginViewController *LoginViewVC = [[LoginViewController alloc] init];
   LoginViewVC.title = @"登录";
KKNavigationController *nav = [[KKNavigationController alloc] initWithRootViewController:LoginViewVC];
self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
self.window.backgroundColor = [UIColor whiteColor];
self.window.rootViewController = nav;
[self.window makeKeyAndVisible];

此时之前的rootViewController即tabViewController并不会释放，需要
self.tabViewController = nil才会释放12e1
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