Background worker populate QListView thumbnails

Question

I have a simple QListview that displays a list of items Names. I would like to display the thumbnail of each item once it has been downloaded. How can i do the following as I'm new to using something like a background worker and I'm not sure how to achieve this.

This explains what i think would be the best approach...

• Use a custom QStyledItemDelegate that overrides the initStyleOption() function.

• Detects the lack of an icon and issues an asynchronous request to load it.

• In the meantime, display default empty icon so user sees placeholder

• When the asynchronous request to download the icon is done, it signals my widget which updates the items icon.

• When i create all of my QStandardModelItems, I give them a custom piece of data (a custom role) that holds the path of the thumbnail for each item

  import os
  import sys
  from PySide2 import QtCore, QtGui, QtWidgets
  
  try:
      # python 2
      from urllib import urlretrieve
      from urllib2 import urlopen
  except Exception as e:
      # python 3
      from urllib.request import urlretrieve, urlopen
  
  import time
  from urllib.parse import urlparse
  
  def getThumbnail(url, output):
      if os.path.exists(output):
          return output
      # # download 1
      # # urlretrieve(url, output)
      # # return os.path.abspath(output)
  
      # download 2
      response = urlopen(url, timeout=5000)
      f = open(output, "wb")
      try:
          f.write(response.read())
      finally:
          f.close()
      return output
  
  class ExampleDialog(QtWidgets.QDialog):
  
      def __init__(self):
          super(ExampleDialog, self).__init__()
  
          self.itemModel = QtGui.QStandardItemModel()
  
          self.uiListView = QtWidgets.QListView()
          # self.uiListView.setViewMode(QtWidgets.QListView.IconMode)
          self.uiListView.setIconSize(QtCore.QSize(80, 60))  #set icon size
          self.uiListView.setGridSize(QtCore.QSize(90, 70)) #set icon grid display
          self.uiListView.setModel(self.itemModel)
  
          self.mainLayout = QtWidgets.QVBoxLayout(self)
          self.mainLayout.addWidget(self.uiListView)
  
          self.populateImages()
  
  
      def populateImages(self):
          root = os.path.join(os.getenv('APPDATA'), 'MyApp\\cache')
          if not os.path.exists(root):
              os.makedirs(root)
  
          print('IMAGES:', root)
  
          for x in range(20):
              url = 'https://picsum.photos/id/{}/80/60.jpg'.format(x)
  
              p = urlparse(url).path
              ext = os.path.splitext(p)[-1]
              output = os.path.join(root, '{}{}'.format(x, ext))
  
              # get thumbnail
              getThumbnail(url, output)
  
              # Item
              item = QtGui.QStandardItem('{}'.format(x))
              item.setData(QtGui.QPixmap(output), QtCore.Qt.DecorationRole)
              item.setData(output, QtCore.Qt.UserRole)
              self.itemModel.appendRow(item)
  
  if __name__ == '__main__':
      app = QtWidgets.QApplication(sys.argv)
      window =  ExampleDialog()
      window.show()
      window.raise_()
      sys.exit(app.exec_())
  

Answer 1

Instead of using a background worker you can use QNetworkAccessManager for asynchronous downloading.

from dataclasses import dataclass
from functools import cached_property
import sys

from PySide2 import QtCore, QtGui, QtWidgets, QtNetwork


@dataclass
class IconDownloader(QtCore.QObject):
    url: QtCore.QUrl
    index: QtCore.QPersistentModelIndex
    _parent: QtCore.QObject = None

    def __post_init__(self):
        super().__init__()
        self.setParent(self._parent)

    @cached_property
    def network_manager(self):
        manager = QtNetwork.QNetworkAccessManager()
        manager.finished.connect(self._handle_finished)
        return manager

    def start(self):
        if self.index.isValid():
            request = QtNetwork.QNetworkRequest(self.url)
            request.setAttribute(
                QtNetwork.QNetworkRequest.FollowRedirectsAttribute, True
            )
            self.network_manager.get(request)

    def _handle_finished(self, reply):
        if reply.error() == QtNetwork.QNetworkReply.NoError:
            pixmap = QtGui.QPixmap()
            ok = pixmap.loadFromData(reply.readAll())
            if ok and self.index.isValid():
                model = self.index.model()
                model.setData(
                    QtCore.QModelIndex(self.index), pixmap, QtCore.Qt.DecorationRole
                )
        else:
            print(reply.error(), reply.errorString())
        reply.deleteLater()
        self.deleteLater()


class ExampleDialog(QtWidgets.QDialog):
    def __init__(self):
        super(ExampleDialog, self).__init__()

        self.itemModel = QtGui.QStandardItemModel()

        self.uiListView = QtWidgets.QListView()
        # self.uiListView.setViewMode(QtWidgets.QListView.IconMode)
        self.uiListView.setIconSize(QtCore.QSize(80, 60))  # set icon size
        self.uiListView.setGridSize(QtCore.QSize(90, 70))  # set icon grid display
        self.uiListView.setModel(self.itemModel)

        self.mainLayout = QtWidgets.QVBoxLayout(self)
        self.mainLayout.addWidget(self.uiListView)

        self.populateImages()

    def populateImages(self):
        for x in range(20):
            url = f"https://picsum.photos/id/{x}/80/60.jpg"
            item = QtGui.QStandardItem(f"x")
            self.itemModel.appendRow(item)
            downloader = IconDownloader(
                QtCore.QUrl(url),
                QtCore.QPersistentModelIndex(self.itemModel.indexFromItem(item)),
                self,
            )
            downloader.start()


if __name__ == "__main__":
    app = QtWidgets.QApplication(sys.argv)
    window = ExampleDialog()
    window.show()
    window.raise_()
    sys.exit(app.exec_())