pyqt QGraphicsView implements the scaling function with the mouse as the center

Pay attention to several key points:

1. Initialization

class CustomGraphicsView(QGraphicsView):
    def __init__(self, parent=None):
        super(CustomGraphicsView, self).__init__(parent)
         = QGraphicsScene()
        ()
        (0, 0, 1024, 600)
        # The following initialization code is more important        (True)
        ()   # Turn on as needed        # () # Open as needed        ()
        ()

2. Key implementation function: Redefine the scroll wheel scaling event (the expected effect may not be achieved, please see step 3 or confirm the initialization)

def wheelEvent(self, event: QWheelEvent) -&gt; None:
        if () == :
            mouse_pos = ()
            scene_pos = (mouse_pos) #The mouse is in the scene before zooming            s = 1.2 #Adjust as needed            if(().y() &gt; 0):
                (s,s)
            else:
                (1/s,1/s)
            view_point = (scene_pos) #After scaling, the original scene maps the new mouse position            ().setValue(int(view_point.y()-mouse_pos.y())) #Move the view through the scroll bar            ().setValue(int(view_point.x()-mouse_pos.x()))
            return 
        else:
            return super().wheelEvent(event) # Ensure that the scroll bar can scroll

3. If the expected effect is not reached, all mouse events may need to be rewrited:

def mousePressEvent(self, event: QMouseEvent) -&gt; None:
        if () == :
             = () # Used for mouse drag view        return

def mouseReleaseEvent(self, event: QMouseEvent) -> None:
        pass
        return

def mouseMoveEvent(self, event):
        if () and : # Implement mouse drag view            newpos = ()
            delta = newpos - 
             = newpos
            ().setValue(().value() - ())
            ().setValue(().value() - ())
        return

This record alone, all events of the mouse have not been redefined, which has caused trouble for nearly half a month. Although it has been fixed, I still don’t know why.

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