PyQt 将图像从 URL 加载到 QPixmap 会导致冻结和崩溃

Question

我制作了一个应用程序，该应用程序从网站收集图像的 URL 并将它们逐个显示在显示器上。但是，当您使用 QComboBox 滚动浏览图像时，程序会冻结 2-3 秒，这很烦人，因为要滚动浏览的 URL 超过 100 个。如果您尝试快速滚动，应用程序会崩溃。图片甚至不是那么大（小于300KB），互联网连接已经足够了。有什么解决方案可以解决这个问题吗？

这是代码的sn-p：

from PyQt5.QtWidgets import *
from PyQt5.QtCore import *
from PyQt5.QtGui import *
import urllib.request
import sys

class MainWindow(QMainWindow):

    def __init__(self, *args, **kwargs):
        super(MainWindow, self).__init__(*args, **kwargs)
        self.setWindowTitle(" ")
        lo2 = QVBoxLayout()




        self.pixmap = QPixmap()

        self.widgetIMG = QLabel()
        self.widgetIMG.setAlignment(Qt.AlignHCenter)

        self.widgetList = QComboBox()
        self.widgetList.addItems(['first image','second image', 'third image'])
        self.widgetList.currentIndexChanged.connect(self.Display)
        self.url_list = ['http://cards.hearthcards.net/3062325e.png', 'http://cards.hearthcards.net/4fc517c5.png', 'http://cards.hearthcards.net/6c9f07e2.png']


        lo2.addWidget(self.widgetIMG)
        lo2.addWidget(self.widgetList)
        widget = QWidget()             
        widget.setLayout(lo2)  
        self.setCentralWidget(widget)

    def Display(self, id):
        print(id)
        URL = self.url_list[id]
        img = urllib.request.urlopen(URL).read()

        self.pixmap.loadFromData(img)
        self.widgetIMG.setPixmap(self.pixmap.scaledToHeight(380))


if __name__ == '__main__':

    app = QApplication(sys.argv)
    window = MainWindow()
    window.show()
    sys.exit(app.exec_())

也许有一种方法可以在启动时预加载所有图像并以某种方式暂时缓存这些图像？最佳解决方案是什么？

Answer 1

问题是urllib.request.urlopen()函数阻塞导致窗口冻结，解决方案是在另一个线程中执行该任务并通过信号将信息发送到主线程。

from functools import partial
import sys
import urllib.request


from PyQt5.QtCore import pyqtSignal, pyqtSlot, QObject, Qt, QThread, QTimer
from PyQt5.QtGui import QPixmap
from PyQt5.QtWidgets import (
    QApplication,
    QComboBox,
    QLabel,
    QMainWindow,
    QVBoxLayout,
    QWidget,
)


class Downloader(QObject):
    resultsChanged = pyqtSignal(bytes)

    @pyqtSlot(str)
    def download(self, url):
        img = urllib.request.urlopen(url).read()
        self.resultsChanged.emit(img)


class MainWindow(QMainWindow):
    def __init__(self, parent=None):
        super(MainWindow, self).__init__(parent)
        self.setWindowTitle("")

        self.thread = QThread(self)
        self.thread.start()

        self.downloader = Downloader()
        self.downloader.moveToThread(self.thread)
        self.downloader.resultsChanged.connect(self.on_resultsChanged)

        self.widgetIMG = QLabel(alignment=Qt.AlignHCenter)

        self.widgetList = QComboBox()
        self.widgetList.currentIndexChanged.connect(self.display)
        for text, url in zip(
            ("first image", "second image", "third image"),
            (
                "http://cards.hearthcards.net/3062325e.png",
                "http://cards.hearthcards.net/4fc517c5.png",
                "http://cards.hearthcards.net/6c9f07e2.png",
            ),
        ):
            self.widgetList.addItem(text, url)

        widget = QWidget()
        lo2 = QVBoxLayout(widget)
        lo2.addWidget(self.widgetIMG)
        lo2.addWidget(self.widgetList)
        self.setCentralWidget(widget)

    @pyqtSlot(int)
    def display(self, ix):
        url = self.widgetList.itemData(ix)
        wrapper = partial(self.downloader.download, url)
        QTimer.singleShot(0, wrapper)

    @pyqtSlot(bytes)
    def on_resultsChanged(self, img):
        pixmap = QPixmap()
        pixmap.loadFromData(img)
        self.widgetIMG.setPixmap(pixmap.scaledToHeight(380))

    def closeEvent(self, event):
        self.thread.quit()
        self.thread.wait()
        super().closeEvent(event)


if __name__ == "__main__":

    app = QApplication(sys.argv)
    window = MainWindow()
    window.show()
    sys.exit(app.exec_())

另一种可能的解决方案是使用 Qt Network：

import sys


from PyQt5.QtCore import pyqtSlot, Qt, QUrl
from PyQt5.QtGui import QPixmap
from PyQt5.QtNetwork import QNetworkAccessManager, QNetworkReply, QNetworkRequest
from PyQt5.QtWidgets import (
    QApplication,
    QComboBox,
    QLabel,
    QMainWindow,
    QVBoxLayout,
    QWidget,
)


class MainWindow(QMainWindow):
    def __init__(self, parent=None):
        super(MainWindow, self).__init__(parent)
        self.setWindowTitle("")

        self.manager = QNetworkAccessManager()
        self.manager.finished.connect(self.on_finished)

        self.widgetIMG = QLabel(alignment=Qt.AlignHCenter)

        self.widgetList = QComboBox()
        self.widgetList.currentIndexChanged.connect(self.display)
        for text, url in zip(
            ("first image", "second image", "third image"),
            (
                "http://cards.hearthcards.net/3062325e.png",
                "http://cards.hearthcards.net/4fc517c5.png",
                "http://cards.hearthcards.net/6c9f07e2.png",
            ),
        ):
            self.widgetList.addItem(text, url)

        widget = QWidget()
        lo2 = QVBoxLayout(widget)
        lo2.addWidget(self.widgetIMG)
        lo2.addWidget(self.widgetList)
        self.setCentralWidget(widget)

    @pyqtSlot(int)
    def display(self, ix):
        url = self.widgetList.itemData(ix)
        self.start_request(url)

    def start_request(self, url):
        request = QNetworkRequest(QUrl(url))
        self.manager.get(request)

    @pyqtSlot(QNetworkReply)
    def on_finished(self, reply):
        target = reply.attribute(QNetworkRequest.RedirectionTargetAttribute)
        if reply.error():
            print("error: {}".format(reply.errorString()))
            return
        elif target:
            newUrl = reply.url().resolved(target)
            self.start_request(newUrl)
            return
        pixmap = QPixmap()
        pixmap.loadFromData(reply.readAll())
        self.widgetIMG.setPixmap(pixmap.scaledToHeight(380))


if __name__ == "__main__":

    app = QApplication(sys.argv)
    window = MainWindow()
    window.show()
    sys.exit(app.exec_())

总的来说，我更喜欢第二种解决方案（Qt 风格的解决方案），因为它通过消除应用程序的复杂性来避免使用线程，因为 Qt Network 使用事件循环并且不会阻塞它。