有没有办法通过使用mouseEvents在QGraphicsScene上绘制任何对象，例如Rectanlel

Question

我想通过在QGraphicsScene上使用鼠标事件来绘制矩形

class GraphicsItem(QGraphicsItem):
    def __init__(self, parent):
        super().__init__()
        self.a = 0
        self.b = 0
        self.setFlag(QGraphicsItem.ItemIsFocusable)
        self.setFocus()
        self.screenSize = QDesktopWidget().screenGeometry(0)
        self.screenHeight = self.screenSize.height()
        self.screenWidth = self.screenSize.width()

    def boundingRect(self):
        self.posX = self.pos().x()
        self.posY = self.pos().y()
        return QRectF(0, 0, self.screenWidth, self.screenHeight)

    def paint(self, painter, option, widget):
        painter.setBrush(QBrush(Qt.red))

    def mousePressEvent(self, event): pass

    def mouseReleaseEvent(self, event): pass

    def mouseMoveEvent(self, event): pass

class GraphicsScene(QGraphicsScene):
    def __init__(self, parent):
        super().__init__(parent=parent)
        graphicsitem = GraphicsItem(self)
        self.addItem(graphicsitem)
        self.setBackgroundBrush(QColor(10, 155, 79))
        self.screenSize = QDesktopWidget().screenGeometry(0)
        self.screenHeight = self.screenSize.height()
        self.screenWidth = self.screenSize.width()

class GraphicsView(QGraphicsView):
    def __init__(self, parent):
        super().__init__(parent=parent)
        graphicsscene = GraphicsScene(self)
        self.screenSize = QDesktopWidget().screenGeometry(0)
        self.screenHeight = self.screenSize.height()
        self.screenWidth = self.screenSize.width()
        self.setGeometry(0, 0, self.screenWidth, self.screenHeight)
        self.setScene(graphicsscene)
        self.show()

class Widget(QWidget):
    def __init__(self):
        super().__init__()
        graphicsview = GraphicsView(self)
        self.screenSize = QDesktopWidget().screenGeometry(0)
        self.screenHeight = self.screenSize.height()
        self.screenWidth = self.screenSize.width()
        self.initUI()

    def initUI(self):
        self.setWindowTitle("Graphics View")
        self.setGeometry(0, 0, self.screenWidth, self.screenHeight)
        self.show()

if __name__ == "__main__":
    app = QApplication(sys.argv)
    widget = Widget()
    sys.exit(app.exec_())