清除缓存，有黑色背景（仿环球时报)

点击页面任何处，出现如下情况，效果图如下：

代码：

-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    UIAlertView * alterView = [[UIAlertView alloc]initWithTitle:@"提示" message:@"以清除缓存" delegate:self cancelButtonTitle:nil otherButtonTitles:@"确认", nil];
    [alterView show];

}