//该方法返回NO则childViewController不会自动viewWillAppear和viewWillDisappear对应的方法
- (BOOL)shouldAutomaticallyForwardAppearanceMethods{
return NO;
}
//viewWillAppear调用设置为YES，viewWillDisappear调用设置为NO
[self.customChildViewController beginAppearanceTransition:YES animated:animated];
//对应的DidAppear调用需要成对出现
[self.customChildViewController endAppearanceTransition];
当 shouldAutomaticallyForwardAppearanceMethods 返回NO 的时候 我们就可以手动调用 （viewWillAppear DidAppear）方法
