QListWidget selection is slowing down app?

Question

I'm writing an app where a QListWidget is used to show gifs previews using QMovie. Everything works fine but there's an increasing slow down while I push the button and repopulate the ListWidget. I was thinking that calling QListWidget.clear() will delete the objects from memory but I'm not sure is actually happening. Maybe there's a more efficient way of doing this but I couldn't find anything elsewhere. Here's some code (I cannot give gifs files but any gif should work):

from PySide2 import QtCore, QtGui, QtWidgets
from PySide2.QtCore import *
from PySide2.QtGui import *
from PySide2.QtWidgets import *
import os, glob

class gifPreviewWidget(QWidget):
    def __init__(self, gifPath, parent=None):
        super(gifPreviewWidget, self).__init__(parent)
        label = QLabel()
        label.setScaledContents(True)
        movie = QMovie(gifPath)
        movie.setSpeed(100)
        label.setMovie(movie)
        movie.start()
        nameLabel = QLabel(os.path.split(gifPath)[1].split('.')[0])
        layout = QVBoxLayout()
        layout.addWidget(label)
        print(gifPath)
        self.setLayout(layout)

class gifDelegate(QItemDelegate):
    def __init__(self, parent=None, *args):
        QItemDelegate.__init__(self, parent, *args)

    def paint(self, painter, option, index):
        painter.save()

        # set background color
        painter.setPen(QPen(Qt.NoPen))

        # set selection color
        if option.state & QStyle.State_Selected:
            painter.setBrush(QBrush(Qt.blue))
        else:
            painter.setBrush(QBrush(Qt.NoBrush))
        painter.drawRect(option.rect)
        painter.restore()

class MainUiClass(QtWidgets.QWidget):
    def __init__(self, parent=None):
        super(MainUiClass, self).__init__(parent)
        self.layout=QVBoxLayout()
        self.gifDelegate = gifDelegate()
        self.previewListWidget = QListWidget()
        self.previewListWidget.setViewMode(QtWidgets.QListView.IconMode)
        self.previewListWidget.setResizeMode(QListWidget.Adjust)
        self.previewListWidget.setSelectionMode(QAbstractItemView.ExtendedSelection)
        self.previewListWidget.setMovement(QListView.Static)
        self.previewListWidget.setSpacing(1)
        self.previewListWidget.setItemDelegate(self.gifDelegate)

        self.pushButton = QPushButton('change gif dir')
        self.layout.addWidget(self.previewListWidget)
        self.layout.addWidget(self.pushButton)
        self.setLayout(self.layout)
        self.pushButton.clicked.connect(self.onCategoryClick)

    def onCategoryClick(self):
        filePath = '/PATH/TO/LOTS/OF/GIFS'
        print(filePath+'/*.gif')
        glob.glob(filePath+'/*.gif')
        if glob.glob(filePath+'/*.gif') != []:
            print('ok')
            gifList = glob.glob(filePath+'/*.gif')
            self.previewListWidget.clear()

            for gif in gifList:
                item=QListWidgetItem(self.previewListWidget)
                itemWidget = gifPreviewWidget(gif)
                item.setSizeHint(itemWidget.sizeHint())
                self.previewListWidget.addItem(item)
                self.previewListWidget.setItemWidget(item,itemWidget)

if __name__ == '__main__':
    w = MainUiClass()
    w.show()
    sys.exit(app.exec_())

By pressing the button often, the app starts to slow down a lot.

Answer 1

Usually, you don't have to stop QMovie explicitly when you're about to delete it anyway. But here, it does not get deleted because it is not stopped (it's still playing).

I guess that kind of unexpected behavior is what you pay for when you use a language with a garbage collector.

Solution: stop the movie when the item is deleted. Add

class gifPreviewWidget(QWidget):
    def __del__(self):
        self.movie.stop()