编写一个widget框架的qgraphicsview

这里是一个简单的QGraphicsView widget框架的实现示例：

from PyQt5.QtCore import Qt
from PyQt5.QtGui import QPen, QBrush, QColor
from PyQt5.QtWidgets import QGraphicsView, QGraphicsScene


class MyWidget(QGraphicsView):
    def __init__(self, parent=None):
        super(MyWidget, self).__init__(parent)
        self._scene = QGraphicsScene(self)
        self.setScene(self._scene)
        self.setRenderHint(QPainter.Antialiasing)

    def paintEvent(self, event):
        super(MyWidget, self).paintEvent(event)
        painter = QPainter(self.viewport())
        painter.setRenderHint(QPainter.Antialiasing)
        painter.setPen(Qt.NoPen)
        painter.setBrush(QBrush(QColor(255, 255, 255)))
        painter.drawRect(self.rect())

    def drawLine(self, start, end, color):
        pen = QPen(QColor(color))
        pen.setWidth(2)
        self._scene.addLine(start.x(), start.y(), end.x(), end.y(), pen)

    def drawRect(self, pos, size, color):
        pen = QPen(QColor(color))
        pen.setWidth(2)
        self._scene.addRect(pos.x(), pos.y(), size.width(), size.height(), pen)

    def drawEllipse(self, pos, size, color):
        pen = QPen(QColor(color))
        pen.setWidth(2)
        self._scene.addEllipse(pos.x(), pos.y(), size.width(), size.height(), pen)

    def clear(self):
        self._scene.clear()

这个框架实现了一个自定义的QGraphicsView类，它支持绘制直线、矩形和椭圆，并提供了清除场景的方法。在paintEvent()方法中，我们使用QPainter绘制了一个白色的背景，以便更好地显示绘制的图形。