//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];

}