python - 如何从 python 线程更新 QML ListView？

Question

我正在编写一个小程序，用于从 Reddit 获取提交内容。到目前为止，我的目标只是获取提交内容并将其显示在 QML 中的 ListView 中。我创建了一个基本的 QML 文件，并创建了一个名为“SubmissionModel”的类，该类扩展了“QAbstractListModel”。我使用 PRAW 来获取 reddit 提交内容，效果非常好。

我使用一个名为“fetch”的函数，该函数用从 reddit 获取的新提交内容填充 SubmissionModel 类。然而，这会阻塞 QML View 并使其挂起，直到“fetch”函数退出。

我尝试在另一个 Python 线程中运行“fetch”函数，这会释放 QML View ，但遗憾的是 ListView 不再更新。我正在寻找一种方法，可以在从另一个线程运行 fetch 函数的同时更新 QML 端的 ListView。

获取函数:

def fetch():

    reddit = init_reddit()

    subreddit = reddit.subreddit('LandscapePhotography')
    counter = 0
    for submission in subreddit.submissions(None, time.time()):
        counter += 1
        print(
            "Counter: {} Submission title: {} , Submission URL: {} ,Created at: {}".format(
                counter, submission.title,
                submission.url,
                datetime.datetime.fromtimestamp(int(submission.created)).strftime('%Y-%m-%d %H:%M:%S')))

        model.addSubmission(Submission(submission.title, submission.url,
                                       datetime.datetime.fromtimestamp(int(submission.created)).strftime(
                                           '%Y-%m-%d %H:%M:%S')))
        if counter == 400:
            break

“SubmissionModel”类:

class SubmissionModel(QAbstractListModel):
    NameRole = Qt.UserRole + 1
    LinkRole = Qt.UserRole + 2
    TimeRole = Qt.UserRole + 3

    _roles = {NameRole: b"name", LinkRole: b"link", TimeRole: b"time"}

    def __init__(self, parent=None):
        super(SubmissionModel, self).__init__(parent)

        self._submissions = []

    def addSubmission(self, submission):
        self.beginInsertRows(QModelIndex(), self.rowCount(), self.rowCount())
        self._submissions.append(submission)
        self.endInsertRows()

    def rowCount(self, parent=QModelIndex()):
        return len(self._submissions)

    def data(self, index, role=Qt.DisplayRole):
        try:
            submission = self._submissions[index.row()]
        except IndexError:
            return QVariant()

        if role == self.NameRole:
            return submission.name()

        if role == self.LinkRole:
            return submission.link()

        if role == self.CreateTimeRole:
            return submission.time()

        return QVariant()

    def roleNames(self):
        return self._roles

不带线程的主函数:

if __name__ == '__main__':
    import sys

    app = QGuiApplication(sys.argv)

    model = SubmissionModel()

    view = QQuickView()
    view.setResizeMode(QQuickView.SizeRootObjectToView)
    ctxt = view.rootContext()
    ctxt.setContextProperty('myModel', model)

    view.setSource(QUrl('main.qml'))
    view.show()

    fetch()

    sys.exit(app.exec_())

当应用程序像这样运行时^^它就可以工作了。 UI 会挂起，直到 fetch() 完成，完成后，UI 将使用 SubmissionModel

中的所有提交进行更新。

主线程:

if __name__ == '__main__':
    import sys

    app = QGuiApplication(sys.argv)

    model = SubmissionModel()

    view = QQuickView()
    view.setResizeMode(QQuickView.SizeRootObjectToView)
    ctxt = view.rootContext()
    ctxt.setContextProperty('myModel', model)

    view.setSource(QUrl('main.qml'))
    view.show()

    **thread = threading.Thread(target=fetch)**
    **thread.start()**

    sys.exit(app.exec_())

这使得“fet​​ch”函数在另一个线程上运行。虽然它工作正常，但每次添加提交时都无法更新 UI。事实上，用户界面永远不会随着新提交的内容而更新。

我的理解是 self.beginInsertRows(QModelIndex(), self.rowCount(), self.rowCount()) 和 self.endInsertRows() 方法addSubmission 函数的目的是让 UI 中的 ListView 知道模型已更新。但是，当运行这些方法的函数从另一个线程运行时，这不起作用。有人可以指出我如何从不同的线程更新 ListView 的正确方向吗？

Answer 1

建议使用 PyQt 提供的工具来处理线程:

• QThreadPool 和 QRunnable:

def fetch():
    reddit = init_reddit()

    subreddit = reddit.subreddit("LandscapePhotography")
    counter = 0
    for submission in subreddit.submissions(None, time.time()):
        counter += 1
        print(
            "Counter: {} Submission title: {} , Submission URL: {} ,Created at: {}".format(
                counter,
                submission.title,
                submission.url,
                datetime.datetime.fromtimestamp(
                    int(submission.created)
                ).strftime("%Y-%m-%d %H:%M:%S"),
            )
        )

        submission = Submission(
            submission.title,
            submission.url,
            datetime.datetime.fromtimestamp(int(submission.created)).strftime(
                "%Y-%m-%d %H:%M:%S"
            ),
        )
        QMetaObject.invokeMethod(
            model,
            "addSubmission",
            Qt.QueuedConnection,
            Q_ARG(Submission, submission),
        )
        QThread.msleep(10)

        if counter == 400:
            break


class RedditRunnable(QRunnable):
    def run(self):
        fetch()

然后在main中调用它:

if __name__ == '__main__':
    import sys

    app = QGuiApplication(sys.argv)

    model = SubmissionModel()

    view = QQuickView()
    view.setResizeMode(QQuickView.SizeRootObjectToView)
    ctxt = view.rootContext()
    ctxt.setContextProperty('myModel', model)

    view.setSource(QUrl('main.qml'))
    view.show()

    runnable = RedditRunnable()
    QThreadPool.globalInstance().start(runnable)

    sys.exit(app.exec_())

• 或者使用信号:

def fetch():
    reddit = init_reddit()

    subreddit = reddit.subreddit("LandscapePhotography")
    counter = 0
    message = Message()
    message.submissionSignal.connect(model.addSubmission, Qt.QueuedConnection)
    for submission in subreddit.submissions(None, time.time()):
        counter += 1
        print(
            "Counter: {} Submission title: {} , Submission URL: {} ,Created at: {}".format(
                counter,
                submission.title,
                submission.url,
                datetime.datetime.fromtimestamp(
                    int(submission.created)
                ).strftime("%Y-%m-%d %H:%M:%S"),
            )
        )

        submission = Submission(
            submission.title,
            submission.url,
            datetime.datetime.fromtimestamp(int(submission.created)).strftime(
                "%Y-%m-%d %H:%M:%S"
            ),
        )
        message.submissionSignal.emit(submission)
        QThread.msleep(10)

        if counter == 400:
            break

class Message(QObject):
    submissionSignal = pyqtSignal(Submission)

if __name__ == '__main__':
    import sys

    app = QGuiApplication(sys.argv)

    model = SubmissionModel()

    view = QQuickView()
    view.setResizeMode(QQuickView.SizeRootObjectToView)
    ctxt = view.rootContext()
    ctxt.setContextProperty('myModel', model)

    view.setSource(QUrl('main.qml'))
    view.show()
    thread = threading.Thread(target=fetch)
    thread.start()

    sys.exit(app.exec_())

_{两种方法都可以在下面link中获取.}