選擇系統相簿圖片之後顯示其檔名字

//選擇圖片的時候呼叫
- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info
{
    UIImage *img = [info objectForKey:UIImagePickerControllerEditedImage];
    if (img != nil)
    {
        //獲取圖片的名字
        __block NSString *imageFileName;
        NSURL *imageURL = [info valueForKey:UIImagePickerControllerReferenceURL];
        ALAssetsLibraryAssetForURLResultBlock resultblock = ^(ALAsset *myasset)
        {
            ALAssetRepresentation *representation = [myasset defaultRepresentation];
            imageFileName = [representation filename];
            NSLog(@"imageFileName : %@",imageFileName);
            //檔名字
            v_cert.lbl_file.text = imageFileName;
        };
        
        ALAssetsLibrary *assetslibrary = [[ALAssetsLibrary alloc] init];
        [assetslibrary assetForURL:imageURL
                       resultBlock:resultblock
                      failureBlock:nil];
    }
    //設定上傳的圖片
    v_cert.img_file.image = img;
    [picker dismissViewControllerAnimated:YES completion:nil];
}