警告框

UIAlertController *alertController = [UIAlertController alertControllerWithTitle:@"开始录制!" message:nil preferredStyle:UIAlertControllerStyleAlert];
        UIAlertAction *enterAction = [UIAlertAction actionWithTitle:@"确定" style:UIAlertActionStyleCancel handler:nil];
        [alertController addAction:enterAction];
        [self showDetailViewController:alertController sender:self];