使用模态跳转，Xcode有时候会出现
Presenting view controllers on detached view controllers is discouraged <SetViewController: 0x7fedb94f0f60>.
这样的警告代码，如果你认为你的层次之间没有问题(其实就是层次问题。present出来的模态窗口，禁止再使用present 来弹出其它的子窗口)
解决方法：
把
WithUsViewController *with=[[WithUsViewController alloc]init]; [self presentViewController:with animated:YES completion:nil];
改为：
AppDelegate *delegate = (AppDelegate *)[UIApplication sharedApplication].delegate;
WithUsViewController *with=[[WithUsViewController alloc]init];
[delegate.window.rootViewController presentViewController:with animated:YES completion:^{
}];
即可
关于Presenting view controllers on detached view ...
原文：http://my.oschina.net/rainwz/blog/497697