Question

我不知道关于Qt的第一件事，但我正试图变得厚脸皮并从其他地方借用代码（http://lateral.netmanagers.com.ar/weblog/posts/BB901.html#disqus_thread）。 ;）

我有问题。当我第一次运行test（）时，一切都在游泳。但是，当我第二次运行它时，我会遇到令人讨厌的段错误。我怀疑问题是我没有正确地结束qt的东西。我应该对此程序进行哪些更改以使其多次运行？提前谢谢！

from PyQt4 import QtCore, QtGui, QtWebKit
import logging

logging.basicConfig(level=logging.DEBUG)

class Capturer(object):
    """A class to capture webpages as images"""

    def __init__(self, url, filename, app):
        self.url = url
        self.app = app
        self.filename = filename
        self.saw_initial_layout = False
        self.saw_document_complete = False

    def loadFinishedSlot(self):
        self.saw_document_complete = True
        if self.saw_initial_layout and self.saw_document_complete:
            self.doCapture()

    def initialLayoutSlot(self):
        self.saw_initial_layout = True
        if self.saw_initial_layout and self.saw_document_complete:
            self.doCapture()

    def capture(self):
        """Captures url as an image to the file specified"""
        self.wb = QtWebKit.QWebPage()
        self.wb.mainFrame().setScrollBarPolicy(
            QtCore.Qt.Horizontal, QtCore.Qt.ScrollBarAlwaysOff)
        self.wb.mainFrame().setScrollBarPolicy(
            QtCore.Qt.Vertical, QtCore.Qt.ScrollBarAlwaysOff)
        self.wb.loadFinished.connect(self.loadFinishedSlot)
        self.wb.mainFrame().initialLayoutCompleted.connect(
            self.initialLayoutSlot)
        logging.debug("Load %s", self.url)
        self.wb.mainFrame().load(QtCore.QUrl(self.url))

    def doCapture(self):
        logging.debug("Beginning capture")
        self.wb.setViewportSize(self.wb.mainFrame().contentsSize())
        img = QtGui.QImage(self.wb.viewportSize(), QtGui.QImage.Format_ARGB32)
        painter = QtGui.QPainter(img)
        self.wb.mainFrame().render(painter)
        painter.end()
        img.save(self.filename)
        self.app.quit()

def test():
    """Run a simple capture"""
    app = QtGui.QApplication([])
    c = Capturer("http://www.google.com", "google.png", app)
    c.capture()
    logging.debug("About to run exec_")
    app.exec_()

DEBUG:root:Load http://www.google.com
QObject::connect: Cannot connect (null)::configurationAdded(QNetworkConfiguration) to QNetworkConfigurationManager::configurationAdded(QNetworkConfiguration)
QObject::connect: Cannot connect (null)::configurationRemoved(QNetworkConfiguration) to QNetworkConfigurationManager::configurationRemoved(QNetworkConfiguration)
QObject::connect: Cannot connect (null)::configurationUpdateComplete() to QNetworkConfigurationManager::updateCompleted()
QObject::connect: Cannot connect (null)::onlineStateChanged(bool) to QNetworkConfigurationManager::onlineStateChanged(bool)
QObject::connect: Cannot connect (null)::configurationChanged(QNetworkConfiguration) to QNetworkConfigurationManager::configurationChanged(QNetworkConfiguration)

Process Python segmentation fault (this last line is comes from emacs)

Answer 1

你需要在测试函数之外处理QApplication，有点像单例（这里实际上是合适的）。

你可以做的是检查QtCore.qApp是否是某种东西（或者如果QApplication.instance（）返回None或其他东西），然后只创建你的qApp，否则，使用全局的。

在test（）函数之后它不会被销毁，因为PyQt将应用程序存储在某个地方。

如果你想确保它处理得正确，只需为它设置一个懒惰的初始化单例。

Answer 2

QApplication只应初始化一次！它可以被任意数量的Capture实例使用，但是你应该在mainloop中启动它们。请参阅：https://doc.qt.io/qt-4.8/qapplication.html

您也可以在“app.exec_”之后尝试“del app”，但我不确定结果。（您的原始代码在我的系统上正常运行）

我会使用urllib而不是webkit：

import urllib

class Capturer:
    def capture(self, s_url, s_filename):
        s_file_out, httpmessage = urllib.urlretrieve(s_url, s_filename, self.report)

    def report(self, i_count, i_chunk, i_size):
        print('retrived %5d of %5d bytes' % (i_count * i_chunk, i_size))

def test():
    c = Capturer()
    c.capture("http://www.google.com/google.png", "google1.png")
    c.capture("http://www.google.com/google.png", "google2.png")

if __name__ == '__main__':
    test()

如何正确关闭PyQt QApplication？

2 个答案: