Question

我需要为我的项目截取网站截图。作为开发语言，我使用Python并使用截图我从PyQt使用Webkit。下面的脚本是用于捕获网站的代码（它已被部分修改，但大部分仍然与webscraping.com中的原始网站相同）。

现在我的问题如下：
大部分时间它没有任何问题，但是，有时会发生以下异常。

QPainter::begin: Paint device returned engine == 0, type: QPainter::setRenderHint: Painter must be active to set rendering hints
QPainter::setBrush: Painter not active
QPainter::pen: Painter not active
QPainter::setPen: Painter not active
QPainter::end: Painter not active, aborted

我已经将问题跟踪到了图像的创建

image = QImage(self.page().viewportSize(), QImage.Format_ARGB32)

此行返回的QImage有时是空的 - 我使用.isNull（） - QImage方法检查了这个。
根据Qt文档，如果没有足够的内存来分配新的QImage，就会发生这种情况，但我仍然有足够的可用内存。这个行为是在Windows和Linux上运行时发生的，所以它不应该依赖于一些os依赖的东西，我想。我是Qt和PyQt的新手，所以我希望有人可以帮助我。

from PyQt4.QtCore import *
from PyQt4.QtGui import *
from PyQt4.QtWebKit import *
import sys
import time

# ############################################################# #
# This script is based on the following script:                 #
# https://webscraping.com/blog/Webpage-screenshots-with-webkit/ #
# ############################################################# #

class Screenshot(QWebView):
    _instance = None

    @staticmethod
    def get_instance():
        # TODO: Add a lock around the if including the creation!
        if Screenshot._instance is None:
            Screenshot._instance = Screenshot()

        return Screenshot._instance

    def __init__(self):
        self.app = QApplication(sys.argv)
        QWebView.__init__(self)
        self._loaded = False
        self.loadFinished.connect(self._loadFinished)

    def capture(self, url, output_file):
        self.load(QUrl(url))
        self.wait_load()
        # set to webpage size
        frame = self.page().mainFrame()
        self.page().setViewportSize(frame.contentsSize())
        # render image
        # creating the image. Here it happens that QImage returns a 'Null'-Image
        image = QImage(self.page().viewportSize(), QImage.Format_ARGB32)
        # check if there's no image allocated
        if image.isNull(): 
            print 'image.isNull() is True'
        if image is None:
            print 'image is None is True'
        painter = QPainter(image)
        frame.render(painter)
        painter.end()
        print 'saving', output_file
        image.save(output_file)

    def wait_load(self, delay=0):
        # process app events until page loaded
        while not self._loaded:
            self.app.processEvents()
            time.sleep(delay)
        self._loaded = False

    def _loadFinished(self, result):
        self._loaded = True

if __name__ == '__main__':
    # a simple way to get the exceptions is to try to create multiple screenshots
    sc = Screenshot()
    for i in range(0, 25):
        sc.capture('http://google.de', str(i) + '.png')

    for i in range(25, 50):
        sc.capture('http://de.wikipedia.org', str(i) + '.png')

Answer 1

确定。我已经进一步追踪了这个问题。看起来QWebPages mainFrame的contentsSize有时是（0,0），当它被读取来创建QImage时。

frame = self.page().mainFrame()
self.page().setViewportSize(frame.contentsSize()) # frame.contentsSize() = (0, 0)
image = QImage(self.page().viewportSize(), QImage.Format_ARGB32) # so we're creating here an Image with Width: 0 and Height: 0

所以基本上QImage似乎是Null，因为它创建的大小是（0,0）。
这个问题可以通过检查mainFrames contentsSize是否为（0,0）来解决。如果是（0,0），则需要在QApplication上处理未完成的事件，直到设置新的contentsSize为止。我现在用以下代码执行此操作：

if frame.contentsSize().width() == 0 or frame.contentsSize().height() == 0:
    print 'ContentsSize = (w: {}, h: {})'.format(frame.contentsSize().width(), frame.contentsSize().height())
    count = 0 # used so we're not starting an infinite loop
    while (frame.contentsSize().width() == 0 or frame.contentsSize().height() == 0) and count < 5:
        count += 1
        self.app.processEvents()
        time.sleep(1)

PyQt：QImage（）返回一个＆＃39; Null＆＃39; -Image

1 个答案: