[Interest] ProxyModel for background image download - How to notify sourceModel?

[Philipp Kursawe]

I have a proxymodel that is responsible for background image downloading.
How to I notify the source model (which does not implement setData, doesn't
have to) that an image has been downloaded? My proxy keeps a cache of
downloaded images for every row in the source model

QVariant ProxyModel:data(index, role) {
  if (role == Qt::DecorationRole) {
    if (cache not contains(index)) {
       startBackgroundDownload(QPersistentIndex(index));
       return placeholderimage;
    } else {
      cachedImage;
    }
  }
}

void ProxyModel::onDownloadFinished(index) {
  // how do I force the sourceModel to refresh?
  emit
sourceModel->dataChanged(index, QVector<int>() << Qt::DecorationRole);
}

This works, but I know we should not call signals of other objects
directly. So how would that work otherwise? By connecting the ProxyModels
dataChanged signal to the sourceModel dataChanged signal?
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