iOS push 问题 ： Unbalanced calls to begin/end appearance transitions for xxx

自定义了TabBarController 之后必须实现以下方法，就不会出现 Unbalanced calls to begin/end appearance transitions for xxx！

- (void)viewWillAppear:(BOOL)animated{
    [super viewWillAppear:animated];
    [self.selectedViewController beginAppearanceTransition: YES animated: animated];
}

- (void)viewDidAppear:(BOOL)animated{
    [super viewDidAppear:animated];
    [self.selectedViewController endAppearanceTransition];
}

- (void)viewWillDisappear:(BOOL)animated{
    [super viewWillDisappear:animated];
    [self.selectedViewController beginAppearanceTransition: NO animated: animated];
}

- (void)viewDidDisappear:(BOOL)animated{
    [super viewDidDisappear:animated];
    [self.selectedViewController endAppearanceTransition];
}