PyQt5: drawing multiple rectangles using mouseEvents by implementing QGraphicsScene, QGraphicsView and QGraphicsItem [duplicate] - pyqt5

Question

I have a scene like this
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()
I would like class MyRect(QtWidgets.QGraphicsRectItem) with painter, mouse event and so on to be a draggable rectangle.
all stuff in MyRect
So then I could have many Rectangle to the scene and even after draw line between them and so on (kind of diagram app), but keeping objects related editable options in MyRect, MyLine , ....
I thought :
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()
But I does not work (paint event not initiated whereas mousepressed event in scene is intiated)
I did not find what I wanted through the web so started totry do it by myself. I'm pretty sure it is a must known starting point but I cannot find it

Answer 1

First of all a QGraphicsItem is not a QWidget, so it has those events and does not handle them directly, that's what QGraphicsView and QGraphicsScene do. For example you say that you want to have a moveable rectangle because that task is simple is QGraphicsView, it is not necessary to overwrite:
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_())
If you want to change the way you paint the rectangle you must overwrite the paint() method as shown below:
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_())
Update:
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_())