首先，QGraphicsItem不是QWidget，因此它具有那些事件并且不能直接处理它们，这就是QGraphicsView和QGraphicsScene所做的。例如，您说您想拥有一个可移动的矩形，因为该任务很简单，就是QGraphicsView，因此不必覆盖：
from PyQt5 import QtCore, QtWidgetsclass MainWindow(QtWidgets.QMainWindow): def __init__(self, parent=None): super(MainWindow, self).__init__(parent) scene = QtWidgets.QGraphicsScene(self) view = QtWidgets.QGraphicsView(scene) self.setCentralWidget(view) rect_item = QtWidgets.QGraphicsRectItem(QtCore.QRectF(0, 0, 100, 100)) rect_item.setFlag(QtWidgets.QGraphicsItem.ItemIsMovable, True) scene.addItem(rect_item)if __name__ == '__main__': import sys app = QtWidgets.QApplication(sys.argv) w = MainWindow() w.resize(640, 480) w.show() sys.exit(app.exec_())
如果要更改绘制矩形的方式，则必须覆盖
paint()如下所示的方法：
from PyQt5 import QtCore, QtGui, QtWidgetsclass RectItem(QtWidgets.QGraphicsRectItem): def paint(self, painter, option, widget=None): super(RectItem, self).paint(painter, option, widget) painter.save() painter.setRenderHint(QtGui.QPainter.Antialiasing) painter.setBrush(QtCore.Qt.red) painter.drawEllipse(option.rect) painter.restore()class MainWindow(QtWidgets.QMainWindow): def __init__(self, parent=None): super(MainWindow, self).__init__(parent) scene = QtWidgets.QGraphicsScene(self) view = QtWidgets.QGraphicsView(scene) self.setCentralWidget(view) rect_item = RectItem(QtCore.QRectF(0, 0, 100, 100)) rect_item.setFlag(QtWidgets.QGraphicsItem.ItemIsMovable, True) scene.addItem(rect_item)if __name__ == '__main__': import sys app = QtWidgets.QApplication(sys.argv) w = MainWindow() w.resize(640, 480) w.show() sys.exit(app.exec_())
更新：
from PyQt5 import QtCore, QtGui, QtWidgetsclass GraphicsScene(QtWidgets.QGraphicsScene): def __init__(self, parent=None): super(GraphicsScene, self).__init__(QtCore.QRectF(-500, -500, 1000, 1000), parent) self._start = QtCore.QPointF() self._current_rect_item = None def mousePressEvent(self, event): if self.itemAt(event.scenePos(), QtGui.QTransform()) is None: self._current_rect_item = QtWidgets.QGraphicsRectItem() self._current_rect_item.setBrush(QtCore.Qt.red) self._current_rect_item.setFlag(QtWidgets.QGraphicsItem.ItemIsMovable, True) self.addItem(self._current_rect_item) self._start = event.scenePos() r = QtCore.QRectF(self._start, self._start) self._current_rect_item.setRect(r) super(GraphicsScene, self).mousePressEvent(event) def mouseMoveEvent(self, event): if self._current_rect_item is not None: r = QtCore.QRectF(self._start, event.scenePos()).normalized() self._current_rect_item.setRect(r) super(GraphicsScene, self).mouseMoveEvent(event) def mouseReleaseEvent(self, event): self._current_rect_item = None super(GraphicsScene, self).mouseReleaseEvent(event)class MainWindow(QtWidgets.QMainWindow): def __init__(self, parent=None): super(MainWindow, self).__init__(parent) scene =GraphicsScene(self) view = QtWidgets.QGraphicsView(scene) self.setCentralWidget(view)if __name__ == '__main__': import sys app = QtWidgets.QApplication(sys.argv) w = MainWindow() w.resize(640, 480) w.show() sys.exit(app.exec_())
