Xcode警告Unbalanced calls to begin

通常iOS开发中会自定义Tab，跳转时通常会使如下代码直接跳转：

LZHTabBarController *tabVC = [[LZHTabBarController alloc]init];

[UIApplication sharedApplication].delegate.window.rootViewController = tabVC;

这个时候Xcode会警告Unbalancedcalls tobegin/endappearance transitionsfor<TabBarController:0x160806c00>.

原因就是控制器跳转时动画未结束就立马进行下一步，解决方法就是通过GCD延时让动画先结束再跳转，代码如下：

dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(0.1 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{

              LZHTabBarController *tabVC = [[LZHTabBarController alloc]init];

              [UIApplication sharedApplication].delegate.window.rootViewController = tabVC;

   });

建议延时最低0.1s，保证动画能够结束，太长会影响跳转视觉效果

同时也可在自定义的Tab中添加如下代码预防问题：

-(void)viewWillAppear:(BOOL)animated

{

    [self.selectedViewController beginAppearanceTransition: YES animated: animated];

}

-(void)viewDidAppear:(BOOL)animated

{

    [self.selectedViewController endAppearanceTransition];

}

-(void) viewWillDisappear:(BOOL)animated

{

    [self.selectedViewController beginAppearanceTransition: NO animated: animated];

}

-(void) viewDidDisappear:(BOOL)animated

{

    [self.selectedViewController endAppearanceTransition];

}