Select items with RubberBandDrag only when it's released

Question

I have a QGraphicsScene where I have QGraphicsItems and enabled rubberBand selection. I want to select these items with rubberband selection but I want them to become selected only when the rubber band is released. Now it selects/deselects items live time. So, items must get selected only when I release the rubberband. I think I might need to completely change the way I add the rubber band but I don't quite know how.

ui_path = "C:/Users/User/ui/button_test.ui"

class Test(QtWidgets.QWidget):
    def __init__(self):
        super(Test, self).__init__()

        loader = QtUiTools.QUiLoader()
        self.ui = loader.load(ui_path, self)

        self.scene = QtWidgets.QGraphicsScene()
        self.ui.graphics_view.setScene(self.scene)

        self.ui.create_rect.clicked.connect(self.itemAdd) # create_rect is a QPushButton
    
        self.ui.graphics_view.setDragMode(QGraphicsView.RubberBandDrag)

        self.setWindowFlags(QtCore.Qt.Window | QtCore.Qt.CustomizeWindowHint | Qt.WindowStaysOnTopHint)

    def itemAdd(self, event):
        
        pen = QPen(Qt.GlobalColor.lightGray)
        pen.setWidth(10)

        brush = QBrush(Qt.GlobalColor.lightGray)

        rect = self.scene.addRect(0, 0, 40, 40, pen, brush)
      
        rect.setFlag(QGraphicsItem.ItemIsMovable)
        rect.setFlag(QGraphicsItem.ItemIsFocusable)
        rect.setFlag(QGraphicsItem.ItemIsSelectable)
        


if __name__ == '__main__':
    win = Test()
    win.ui.show()

Also I want to make my rubberband area colored and semi-transparent. I've read the docs but can't correctly implement everything that I've read. Any help would be greatly appreciated!

Answer 1

A possible solution is to create a "fake" rubber band, a widget that is child of the view (or, better, the viewport).

While QGraphicsView does it in the paintEvent (with a "virtual" rectangle painted over the view), using a child widget avoids overriding of the paint event and provides more control over its behavior.

class Test(QWidget):
    def __init__(self):
        # ...
        self.ui.graphics_view.viewport().installEventFilter(self)
        self.rubberBand = None

    def eventFilter(self, obj, event):
        if event.type() == event.MouseButtonPress and event.button() == Qt.LeftButton:
            # if there is no item at the mouse position, create a rubber band
            if not self.ui.graphics_view.itemAt(event.pos()) and not self.rubberBand:
                self.createRubberBand(event.pos())
        elif event.type() == event.MouseMove and self.rubberBand:
            self.updateRubberBand(event.pos())
        elif event.type() == event.MouseButtonRelease and self.rubberBand:
            self.finalizeRubberBand()
        return super().eventFilter(obj, event)

    def createRubberBand(self, pos):
        # create a rubber band as child widget of the *viewport*
        self.rubberBand = QWidget(self.ui.graphics_view.viewport())
        # store the start position to get the proper rectangle when dragging
        self.rubberBand.start = pos

        # use the palette to get the default selection color and
        # make it semi transparent for the background
        background = self.palette().color(QPalette.Highlight)
        background.setAlphaF(.5)
        self.rubberBand.setStyleSheet('''
            border: 1px solid palette(highlight); 
            background: {};
        '''.format(background.name(background.HexArgb)))

        self.rubberBand.setGeometry(pos.x(), pos.y(), 0, 0)
        self.rubberBand.show()

    def updateRubberBand(self, pos):
        # update the rectangle based on start and mouse position, since the result
        # could be a rectangle with negative width or height, we need to "normalize"
        # as widget geometries can only have positive dimensions
        rect = QRect(self.rubberBand.start, pos).normalized()
        self.rubberBand.setGeometry(rect)

    def finalizeRubberBand(self):
        # map the geometry of the rubber band to the scene
        area = self.ui.graphics_view.mapToScene(self.rubberBand.geometry())
        path = QPainterPath()
        path.addPolygon(area)
        self.scene.setSelectionArea(path)
        # remove the rubber band
        self.rubberBand.deleteLater()
        self.rubberBand = None