无法使用QWebEnginePage::runJavaScript()更改backgroundImage

Question

我最初想解决这个问题，但由于我已经测试了QWebEnginePage:runJavaScript()的行为，我发现我甚至不能使用QWebEnginePage::runJavaScript()用下面的代码更改backgroundImage，那么为什么呢？

import sys

from PyQt5.QtGui import *
from PyQt5.QtCore import *
from PyQt5.QtWidgets import *
from PyQt5.QtWebEngineWidgets import *
from PyQt5.QtWebEngineCore import *


class WebEngineView(QWebEngineView):
    def __init__(self, parent=None):
        super().__init__(parent)

        self.webPage = self.page()
        # self.webPage = WebEnginePage()
        self.webPage.load(QUrl('https://developer.mozilla.org/en-US/docs/Web/API/HTMLElement/style'))
        self.webPage.runJavaScript('''
                                window.addEventListener("load", function(event) {
                                        alert(document.title);
                                        document.body.style.backgroundImage = "url('https://www.w3schools.com/jsref/img_tree.png')";

                                });
                     ''')  # QWebEngineScript.MainWorld


if __name__ == "__main__":

    app = QApplication(sys.argv)
    app.setAttribute(Qt.AA_UseSoftwareOpenGL)
    webEngineView = WebEngineView()
    webEngineView.show()
    sys.exit(app.exec_())

Answer 1

您希望修改DOM，因此必须已经创建了它，在您的示例中，在加载页面和未构建DOM之前使用runJavaScript。考虑到有两种可能的解决办法：

• 加载页面后，使用loadFinished信号执行脚本：

import sys
from PyQt5 import QtCore, QtWidgets, QtWebEngineWidgets


class WebEngineView(QtWebEngineWidgets.QWebEngineView):
    def __init__(self, parent=None):
        super().__init__(parent)
        self.loadFinished.connect(self.on_load_finished)

        self.load(
            QtCore.QUrl(
                "https://developer.mozilla.org/en-US/docs/Web/API/HTMLElement/style"
            )
        )

    @QtCore.pyqtSlot(bool)
    def on_load_finished(self, ok):
        if ok:
            script = """
            alert(document.title);
            document.body.style.backgroundImage = "url('https://www.w3schools.com/jsref/img_tree.png')";
            """
            self.page().runJavaScript(script)


if __name__ == "__main__":
    QtCore.QCoreApplication.setAttribute(QtCore.Qt.AA_ShareOpenGLContexts)
    QtCore.QCoreApplication.setAttribute(QtCore.Qt.AA_UseSoftwareOpenGL)
    app = QtWidgets.QApplication(sys.argv)
    w = WebEngineView()
    w.show()
    sys.exit(app.exec_())

• 使用QWebEngineScript实现允许注入javascript代码的user script：

import sys

from PyQt5 import QtCore, QtWidgets, QtWebEngineWidgets


class WebEngineView(QtWebEngineWidgets.QWebEngineView):
    def __init__(self, parent=None):
        super().__init__(parent)

        script = QtWebEngineWidgets.QWebEngineScript()
        name = "test"
        source = """
        alert(document.title);
        document.body.style.backgroundImage = "url('https://www.w3schools.com/jsref/img_tree.png')";
        """
        script.setName(name)
        script.setSourceCode(source)
        script.setInjectionPoint(
            QtWebEngineWidgets.QWebEngineScript.DocumentReady
        )
        script.setRunsOnSubFrames(True)
        script.setWorldId(QtWebEngineWidgets.QWebEngineScript.ApplicationWorld)
        self.page().scripts().insert(script)

        self.load(
            QtCore.QUrl(
                "https://developer.mozilla.org/en-US/docs/Web/API/HTMLElement/style"
            )
        )


if __name__ == "__main__":
    QtCore.QCoreApplication.setAttribute(QtCore.Qt.AA_ShareOpenGLContexts)
    QtCore.QCoreApplication.setAttribute(QtCore.Qt.AA_UseSoftwareOpenGL)
    app = QtWidgets.QApplication(sys.argv)
    w = WebEngineView()
    w.show()
    sys.exit(app.exec_())