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  1. Qt for Python
  2. PYSIDE-892

QQmlEngine.contextForObject always returns None

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    Details

    • Type: Bug
    • Status: Closed
    • Priority: P3: Somewhat important
    • Resolution: Done
    • Affects Version/s: 5.12.0
    • Fix Version/s: 5.12.1
    • Component/s: PySide
    • Labels:
      None
    • Platform/s:
      Linux/X11
    • Commits:
      ff8f597b4581efa48074286cac6f9f1eb1827cd0 (pyside/pyside-setup/5.12)

      Description

      I'm trying to do something like this example, except in Python (from http://doc.qt.io/qt-5/qqmlcomponent.html#engine ): 

       

      void MyCppItem::init()
      {
          QQmlEngine *engine = qmlEngine(this);
          // Or:
          // QQmlEngine *engine = qmlContext(this)->engine();
          QQmlComponent component(engine, QUrl::fromLocalFile("MyItem.qml"));
          QQuickItem *childItem = qobject_cast<QQuickItem*>(component.create());
          childItem->setParentItem(this);
      }
      

       

      In Python there appears to be no qmlContext or qmlEngine function, but an alternative is available via QQmlEngine.contextForObject. Unfortunately, I can't get this to return anything other than None. According to the docs (http://doc.qt.io/qt-5/qqmlengine.html#contextForObject) the context for any QObject should be "set automatically" by the QQmlEngine, after the object is constructed.

      I also ran across this question (https://stackoverflow.com/questions/51946711/access-to-a-qqmlapplicationengine-inside-my-custom-class) from someone writing a C++ program that calls this function, and they appear to be observing similar behavior.

      Here's some example code to demonstrate the issue.

      QML:

      import QtQuick          2.0
      import QtQuick.Controls 2.2
      
      Rectangle {
          width: 200; height: 200
      
          Button {
            text: "print Hello World"
            onClicked: MainWindow.Print('hello world')
          }
      }
      
      
      

       

      Python:

      #!/bin/env python3
      # -*- coding: utf-8 -*-
      from PySide2.QtCore    import Slot
      from PySide2.QtCore    import QUrl
      from PySide2.QtQml     import qmlRegisterType
      from PySide2.QtQml     import QQmlEngine
      from PySide2.QtQuick   import QQuickView
      from PySide2.QtQuick   import QQuickItem
      from PySide2.QtWidgets import QApplication
      import sys
      
      class MainWindow(QQuickView):
          def __init__(self):
              super().__init__()
              self.setSource(QUrl('sample.qml'))
              self.rootContext().setContextProperty("MainWindow", self)
              self.show()
      
          @Slot('QString')
          def Print(self, value):
              print(value)
              print("context=" + str(QQmlEngine.contextForObject(self)))
      
      
      if __name__ == '__main__':
          app = QApplication(sys.argv)
          w = MainWindow()
          sys.exit(app.exec_())
      
      

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            • Assignee:
              kleint Friedemann Kleint
              Reporter:
              nels David Friberg
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              Dates

              • Created:
                Updated:
                Resolved:

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