presentViewController
メソッドを非同期で呼び出すメカニズムはありますか?
UIImagePickerController *imagePicker = [[UIImagePickerController alloc]init];
imagePicker.delegate = self;
imagePicker.sourceType = UIImagePickerControllerSourceTypeCamera;
imagePicker.mediaTypes = @[(NSString *) kUTTypeImage];
imagePicker.allowsEditing = NO;
[self.viewController presentViewController:imagePicker animated:YES completion:nil];