一，效果图。
二，代码。
RootViewController.m
//点击任何处出现sheet
-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
UIActionSheet * sheet = [[UIActionSheet alloc] initWithTitle:@"确定要清空图片缓存？" delegate:self cancelButtonTitle:@"取消" destructiveButtonTitle:@"确定" otherButtonTitles:nil, nil];
[sheet showInView:self.view];
}
原文：http://www.cnblogs.com/yang-guang-girl/p/5500292.html