概念：deprecated 弃用。表示已不被建议使用，可能随时取消它；建议采用新的来替代。
"modalViewController" 属性 is deprecated : first deprecated in iOS 6.0
而采用
presentedViewController
"dismissModalViewControllerAnimated" is deprecated : first deprecated in iOS 6.0
而采用
dismissViewControllerAnimated:(BOOL) completion:^(void)completion
如：[self dismissViewControllerAnimated:YES completion:nil];
"presentModalViewController: animated:" is deprecated : first deprecated in iOS 6.0
而采用
presentViewController:(UIViewController *) animated:(BOOL) completion:^(void)completion
如：[self.viewController presentViewController:controller animated:YES completion:nil];
"automaticallyForwardAppearanceAndRotationMethodsToChildViewControllers" is deprecated : first deprecated in iOS 6.0
而采用
shouldAutomaticallyForwardRotationMethods 和 shouldAutomaticallyForwardAppearanceMethods
"shouldAutorotateToInterfaceOrientation:" is deprecated : first deprecated in iOS 6.0
而采用
重载 supportedInterfaceOrientations 和 preferredInterfaceOrientationForPresentation 方法
"viewDidUnload"和"viewWillUnload" 在iOS 6.0从不调用。