Dropzone

A Flutter Web plugin to handle drag-and-drop (files) into Flutter. If you're interested in drag-and-drop inside a Flutter app, check out other packages like dnd.

It exposes a single platform view, DropzoneView:

DropzoneView(
  operation: DragOperation.copy,
  cursor: CursorType.grab,
  onCreated: (ctrl) => controller = ctrl,
  onLoaded: () => print('Zone loaded'),
  onError: (ev) => print('Error: $ev'),
  onHover: () => print('Zone hovered'),
  onDrop: (ev) => print('Drop: $ev'),
  onLeave: () => print('Zone left'),
);

The view itself has no display, it's just the dropzone area. Use a Stack to put it into the background of other widgets that provide your UI:

Stack(
  children: [
    DropzoneView(...),
    Center(child: Text('Drop files here')),
  ],
)

Using it in cross-platform apps

It's a federated plugin, meaning that it will compile in cross platform apps that contain both Android/iOS and Web code. It will not function on the latter, the view will simply return an error text instead of a drop zone. Use if (kIsWeb) from import 'package:flutter/foundation.dart' to only use it in Flutter Web. Still, the same app will still compile to Android and iOS, without the usual dart:html errors (this is what federated plugins are for).

Using the controller

There is a convenience function, pickFiles() on the controller returned by the view. It simply opens the usual File Open dialog in the browser and lets the user pick some files. It has nothing to do with the drag-and-drop operation (although it is the other possible way to select files) but by putting it into the web side of a federated plugin we can make sure it doesn't hurt the compilation on other platforms.

Because the files returned are HTML File API references with serious limitations, they can't be converted to regular Dart File objects. They are returned as dynamic objects and the controller has functions to extract information from these objects:

  • Future<String> getFilename(dynamic htmlFile);
  • Future<int> getFileSize(dynamic htmlFile);
  • Future<String> getFileMIME(dynamic htmlFile);
  • Future<Uint8List> getFileData(dynamic htmlFile);

You can't have a permanent link to the file. If you need to retain the full image data, use getFileData() to get the actual contents and store it yourself into localStorage, IndexedDB, uploading to your server, whatever. You can get a temporary URL using:

  • Future<String> createFileUrl(dynamic htmlFile);
  • Future<bool> releaseFileUrl(String fileUrl);

but this will only be valid for the session. It's a regular URL, so you can use it to display the image the same way like loading from a regular web URL. Release it when you're done with the image.

Libraries

flutter_dropzone