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Subclass QUiLoader



  • I am subclassing QUiLoader so that I can control the widgets created in createWidget. My code is something like this:

    from importlib import import_module
    
    class MyLoader(QUiLoader):
        def __init__(self):
            super().__init__()
            self.widget_mod = import_module("PySide2.QtWidgets")
    
        def createWidget(self, class_name, parent=None, name=''):
            orig_widget_inst = QUiLoader.createWidget(self, class_name, parent=None, name='')
            my_widget_inst = getattr(self.widget_mod, class_name)(parent)
            return my_widget_inst
    

    my_widget_inst appears to be equivalent to orig_widget_inst, but mine causes a segmentation fault. What else do I need to do to make my_widget_inst usable?


  • Lifetime Qt Champion

    Hi,

    @3beezer said in Subclass QUiLoader:

    def createWidget(self, class_name, parent=None, name=''):
    orig_widget_inst = QUiLoader.createWidget(self, class_name, parent=None, name='')
    widget_widget_inst = getattr(self.widget_mod, class_name)(parent)
    return my_widget_inst

    You are talking about my_widget_inst in your post but you don't have anything named like that created in your code. Is it just a typo ?



  • @sgaist Typo. I fixed it. Sorry.


  • Lifetime Qt Champion

    Can you add a minimal sample code that uses this class and triggers the issue ?



  • test.py

    import sys
    from importlib import import_module
    
    from PySide2.QtCore import QFile
    from PySide2.QtUiTools import QUiLoader
    from PySide2.QtWidgets import QApplication
    
    class MyLoader(QUiLoader):
        def __init__(self):
            super().__init__()
            self.widget_mod = import_module("PySide2.QtWidgets")
    
        def createWidget(self, class_name, parent=None, name=''):
            orig_widget_inst = QUiLoader.createWidget(self, class_name, parent=None, name='')
            print("orig_widget_inst =", orig_widget_inst)
    
            widget_class = getattr(self.widget_mod, class_name)
            my_widget_inst = widget_class(parent)
            print("my_widget_inst =", my_widget_inst)
    
            return orig_widget_inst
            #return my_widget_inst
    
    if __name__ == "__main__":
        app = QApplication(sys.argv)
        ui_file = QFile(sys.argv[1])
        ui_file.open(QFile.ReadOnly)
        loader = MyLoader()
        loader.load(ui_file)
        ui_file.close()
    

    and test.ui

    <?xml version="1.0" encoding="UTF-8"?>
    <ui version="4.0">
     <class>test_panel</class>
     <widget class="QWidget" name="test_panel"/>
     <resources/>
     <connections/>
    </ui>
    

    Run the program using

    python test.py test.ui
    

    Switch the comment on the two return statements to see the crash.



  • I'm new here. Should I report this problem as a bug? If so, where?


  • Lifetime Qt Champion

    What version of PySide2 are you currently using ?
    On what OS ?

    PySide2 5.11.1 and 5.13.0 on macOS are working with your test example.



  • @sgaist Interesting! I am using version 5.12.4 on Kubuntu 19.04 with Python 3.7.3. Oh, I see that I can upgrade PySide2 to 5.13.0 using pip. I will do so and report back.



  • Nope. Still crashes. You did switch the # to the other return, right?


  • Lifetime Qt Champion

    No I didn't because I overlooked it and I must say I expect to run crashing examples with the "working" version in comment rather than the contrary.

    Before digging further, can you just explain what you want to do exactly in createWidget ?



  • I would like to wrap the widget and return an instance of the wrapped widget. Since I can't return an instance of the exact same widget without getting a crash, it doesn't seem to be possible to override createWidget, despite claims to the contrary.


  • Lifetime Qt Champion

    What wrapping do you have in mind ?



  • I have several ideas. One I would have liked to implement earlier today is a subclass with __del__ so that I can confirm that I haven't created a cyclic reference. I do this in portions of the GUI I design manually, but I can't do it in portions I design using Qt Designer.


  • Lifetime Qt Champion

    I wonder if it's a python specific issue.

    Can you test if the same issue happens in C++ ?



  • I think it is, but I don't know C++ well enough to write a test program.



  • The problem is officially a bug:

    bug 1070


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