Python 无法使用ConnectSlotsByName将插槽连接到pqtgraph InfiniteLine信号

每当拖动无限长线时，我都会使用以下代码调用一个函数.它不会调用该函数.

    import sys
    import pyqtgraph as pg
    from PyQt5.QtCore import pyqtSlot as Slot, Qt, QMetaObject
    
    from PyQt5.QtWidgets import *
    from PyQt5.QtCore import *
    from PyQt5.QtGui import *
    
    class MyMainWindow(QMainWindow):
        def __init__(self, parent=None):
            super().__init__(parent=parent)
    
            self.setGeometry(300, 300, 400, 300)
            self.setWindowTitle('Hello World')
    
            self.plot_widget = pg.PlotWidget()
            self.plot_item = self.plot_widget.plot([1,0,2], pen='b', name='p0')
            self.vline = pg.InfiniteLine(movable=True, angle=90)
            self.vline.setObjectName('vline')
            self.plot_widget.addItem(self.vline)
            self.setCentralWidget(self.plot_widget)
            
            QMetaObject.connectSlotsByName(self)
            
        @Slot(object)
        def on_vline_sigDragged(self, obj):
            print('dragged')
            
    if __name__ == "__main__":
        app = QApplication(sys.argv)
        ui = MyMainWindow()
        ui.show()
        sys.exit(app.exec_()) 

但当我通过以下方式手动分配插槽时

    self.vline.sigDragged.connect(self.on_vline_sigDragged)

它工作得很好.

为什么会这样呢？