FlutterArtist BackgroundWebDownloadAction Example

BackgroundWebDownloadAction

BackgroundWebDownloadAction is a built-in class in FlutterArtist that facilitates downloading binary data requiring browser-based authentication, specifically designed for Flutter Web applications.

BackgroundWebDownloadAction

abstract class BackgroundWebDownloadAction extends BackgroundAction {
  final String fileName;

  BackgroundWebDownloadAction({
    required this.fileName,
    required super.needToConfirm,
    required super.actionInfo,
  });

  Future<ApiResult<List<int>?>> performDownload();
	
  // Other codes..
}

Example Scenario: Demo17a

The main screen of the example displays a product list. Users click on a product to view its details, then click the Download button to download the product image.

You might wonder why such a complex BackgroundWebDownloadAction is needed just to download an image. The answer lies in security. If the image data is protected, you must send an authenticated download request. The combination of BackgroundWebDownloadAction and FlutterArtistDio enables you to handle this seamlessly.

Download FlutterArtist Demo
FlutterArtist Action (***)
FlutterArtist Dio

1. BackgroundWebDownloadAction

First, we create the UrlDownloadHelper class with a downloadUrl() method that accepts a URL and returns binary data.

url_download_helper.dart

class UrlDownloadHelper {
  Future<ApiResult<List<int>?>> downloadUrl(String url) async {
    ApiResult<List<int>?> result =
        await flutterArtistDio4Download.binaryGet(url);
    return result;
  }
}

In the code above, flutterArtistDio4Download is a FlutterArtistDio instance used for binary data transmission. In the FlutterArtist Demo, this object is pre-configured in "config/fa_dio.dart". For your own projects, follow the guide to create a similar object here:

FlutterArtist Dio

DownloadProduct17aImageAction

Now, we extend BackgroundWebDownloadAction to define the product image download action:

download_product17a_image_action.dart

///
/// Download a URL with Browser.
///
class DownloadProduct17aImageAction extends BackgroundWebDownloadAction {
  final String downloadUrl;

  final urlDownloadHelper = UrlDownloadHelper();

  DownloadProduct17aImageAction({
    required this.downloadUrl,
    required super.fileName,
    required super.needToConfirm,
    required super.actionInfo,
  });

  @override
  Future<ApiResult<List<int>?>> performDownload() async {
    return await urlDownloadHelper.downloadUrl(downloadUrl);
  }

  @override
  CustomConfirmation? createCustomConfirmation() {
    return null;
  }
}

Make sure the "Download" button only appears when there is a current product and the imageUrl is not null.

if (productData != null && productData.imageUrl != null)
  TextButton(
    onPressed: () {
      _downloadImage(
        productName: productData.name,
        imageUrl: productData.imageUrl!,
      );
    },
    child: Text("Download Image"),
  ),

When the user clicks the button, the _downloadImage() method is called. Here, we create a DownloadProduct17aImageAction instance and execute it via the backgroundExecutor.

void _downloadImage({
  required String productName,
  required String imageUrl,
}) {
  FlutterArtist.codeFlowLogger.addMethodCall(
    ownerClassInstance: this,
    currentStackTrace: StackTrace.current,
    parameters: null,
  );
  //
  final action = DownloadProduct17aImageAction(
    downloadUrl: imageUrl,
    fileName: "$productName.png",
    needToConfirm: true,
    actionInfo: 'Download Product Image',
  );
  FlutterArtist.backgroundExecutor.executeBackgroundAction(
    action: action,
  );
}

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FlutterArtist BackgroundWebDownloadAction Example

1. BackgroundWebDownloadAction

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