pyqt在Qgraphicsscene中添加矩形

Question

我有这样的场景

class Scene(QtWidgets.QGraphicsScene):
    def __init__(self, parent=None):
        super(Scene, self).__init__(parent)

    def mousePressEvent(self, event):
        print('scene pressed')
        self.wid = MyRect(event.pos(), event.pos())
        self.addItem(self.wid)
        self.wid.show()

我希望带有画家、鼠标事件等的 MyRect(QtWidgets.QGraphicsRectItem) 类是一个可拖动的矩形。 MyRect 中的所有内容

所以我可以在场景中有很多矩形，甚至在它们之间画线之后等等（一种图表应用程序），但在 MyRect、MyLine 等中保留与对象相关的可编辑选项。

我想：

class MyRect(QtWidgets.QGraphicsRectItem):
    def __init__(self, begin, end, parent=None):
        super().__init__(parent)
        self.begin = begin
        self.end = end

    def paintEvent(self, event):
        print('painting')
        qp = QtGui.QPainter(self)
        qp.drawRect(QtCore.QRect(self.begin, self.end))

    def mousePressEvent(self, event):
        self.begin = event.pos()
        self.end = event.pos()
        self.update()

    def mouseMoveEvent(self, event):
        self.end = event.pos()
        self.update()

    def mouseReleaseEvent(self, event):
        self.begin = event.pos()
        self.end = event.pos()
        self.update()

但我不工作（绘制事件未启动，而场景中的 mousepressed 事件已启动）

我没有通过网络找到我想要的东西，所以开始尝试自己做。我很确定这是一个必须知道的起点，但我找不到它

Answer 1

首先，QGraphicsItem 不是 QWidget，所以它有那些事件并且不直接处理它们，这就是 QGraphicsView 和 QGraphicsScene 所做的。比如你说你想要一个可移动的矩形，因为那个任务很简单，就是 QGraphicsView，没必要覆盖：

from PyQt5 import QtCore, QtWidgets

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 = 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_())

---

如果你想改变绘制矩形的方式，你必须覆盖paint()方法，如下所示：

from PyQt5 import QtCore, QtGui, QtWidgets


class 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, QtWidgets

class 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_())