I have a ImageManager class that extends ChangeNotifier.

class ImageManager extends ChangeNotifier {
  final List<LocalImage> _images = [];

  List<LocalImage> get images => _images;

  bool get isEmpty => _images.isEmpty;

  void addImage(LocalImage image) {
    _images.add(image);
    notifyListeners();
  }   

  void clear() {
    _images.clear();
    notifyListeners();
  }

  Uint8List? getImageData(String referenceId) {
    for (var image in _images) {
      if (image.referenceId == referenceId) {
        return image.imageData;
      }
    }
    notifyListeners();
    return null;
  }
}

As you can see I have a list of LocalImage.

Here is how I am using it:

  _someFunc() async {
    final ImagePicker _picker = ImagePicker();
    XFile? xFile = await _picker.pickImage(source: ImageSource.gallery);

    Uint8List bytes = await xFile!.readAsBytes();
    var referenceId = DateTime.now().millisecondsSinceEpoch.toString();

    /**
     * Create a new instance of LocalImage
     */
    LocalImage newInstance = LocalImage(randomId, bytes);
    ImageManager().addImage(newInstance);

    widget.item.referenceId = randomId;
  }

I am storing the reference id in a separate object. So I am using the referenceId to fetch the Uint8List bytes to build an image:

  Widget _buildImage() {
    return kIsWeb
        ? Consumer<ImageManager>(
            builder: (context, model, _) {
              if (!model.isEmpty) {
                print('image manager is not empty');
                return Image.memory(
                  model.getImageData(widget.item.referenceId)!,
                  ...////
                );
              } else {
                print('image manager is empty: ${model.images.length}');
                return _buildPicker();
              }
            },
          )
        : _buildImageMob();
  }

But I am always getting image manager is empty. So why is the list still empty even after I add the LocalImage object to the list?

CodePudding user response：

When you call ImageManager().addImage, you are making a new instance of ImageManager, instead, you want to use Provider.of<ImageManager>(context).addImage and make sure your context can reach your provider.