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];