Make QGraphicsItem only selectable in one graphicsview

Question

I have a setup where two QGraphicViews display a single QGraphicsScene. One of these views is an overview the other the detail. Imagine something like:

The rectangle marking the current boundaries of the detailed view is part of the scene. It is the white rectangle in the upper view, which I will call in the text below as "bounding-box".

What I want is to be able to click in the overview- QGraphicsView and drag the bounding-box around to trigger a scrolling of the detail- QGraphicsView. Obviously, the bounding-box has to be only clickable in the overview- QGraphicsView, otherwise I would never be able to do manipulations in the detail- QGraphicsView, because the bounding-box covers the entire detail view.

So how can I make a QGraphicsItem be selectable only from a single QGraphicsView or, alternatively, how do I "insert" a QGraphicsItem only into a single QGraphicsView? Can I perhaps nest QGraphicsScenes so that one is the copy of another plus some extra items?

Answer 1

Extending the answer of Trilarion, I was able to solve the problem, by installing a Eventfilter on the overview QgraphcisView. On the Enter event, the dragging is enabled, on the Leave event the dragging is disabled.

from PySide import QtGui, QtCore

# special GraphicsRectItem that is aware of its position and does something if the position is changed
class MovableGraphicsRectItem(QtGui.QGraphicsRectItem):

    def __init__(self, callback=None):
        super(MovableGraphicsRectItem, self).__init__()
        self.setFlags(QtGui.QGraphicsItem.ItemIsMovable | QtGui.QGraphicsItem.ItemSendsScenePositionChanges)
        self.setCursor(QtCore.Qt.PointingHandCursor)
        self.callback = callback

    def itemChange(self, change, value):
        if change == QtGui.QGraphicsItem.ItemPositionChange and self.callback:
            self.callback(value)

        return super(MovableGraphicsRectItem, self).itemChange(change, value)

    def activate(self):
        self.setFlags(QtGui.QGraphicsItem.ItemIsMovable | QtGui.QGraphicsItem.ItemSendsScenePositionChanges)
        self.setCursor(QtCore.Qt.PointingHandCursor)

    def deactivate(self):
        self.setFlags(not QtGui.QGraphicsItem.ItemIsMovable | QtGui.QGraphicsItem.ItemSendsScenePositionChanges)
        self.setCursor(QtCore.Qt.ArrowCursor)


class MouseInsideFilterObj(QtCore.QObject):#And this one
    def __init__(self, enterCallback, leaveCallback):
        QtCore.QObject.__init__(self)
        self.enterCallback = enterCallback
        self.leaveCallback = leaveCallback

    def eventFilter(self, obj, event):
        if event.type() == QtCore.QEvent.Type.Enter:
            self.enterCallback(obj)

        if event.type() == QtCore.QEvent.Type.Leave:
            self.leaveCallback(obj)

        return True


class TestClass:

    def __init__(self):

        self.app = QtGui.QApplication([])

        # the scene with some rectangles
        self.scene = QtGui.QGraphicsScene()
        self.scene.addRect(30, 30, 100, 50, pen=QtGui.QPen(QtCore.Qt.darkGreen))
        self.scene.addRect(150, 0, 30, 80, pen=QtGui.QPen(QtCore.Qt.darkYellow))
        self.scene.addRect(80, 80, 100, 20, pen=QtGui.QPen(QtCore.Qt.darkMagenta))
        self.scene.addRect(200, 10, 30, 80, pen=QtGui.QPen(QtCore.Qt.darkRed))

        self.window = QtGui.QWidget()

        # put two graphicsviews into the window with different scaling for each
        self.layout = QtGui.QVBoxLayout(self.window)
        self.v1 = QtGui.QGraphicsView(self.scene)
        self.v1.setFixedSize(500, 100)
        self.v1.scale(0.5, 0.5)
        self.v1.setHorizontalScrollBarPolicy(QtCore.Qt.ScrollBarAlwaysOff)
        self.v1.setVerticalScrollBarPolicy(QtCore.Qt.ScrollBarAlwaysOff)
        self.layout.addWidget(self.v1) 
        self.v2 = QtGui.QGraphicsView(self.scene)
        self.v2.setFixedSize(500, 500)
        self.v2.scale(5, 5)
        self.v2.setHorizontalScrollBarPolicy(QtCore.Qt.ScrollBarAlwaysOff)
        self.v2.setVerticalScrollBarPolicy(QtCore.Qt.ScrollBarAlwaysOff)
        self.layout.addWidget(self.v2)

        mouseFilter = MouseInsideFilterObj(self.enterGV, self.leaveGV)
        self.v1.installEventFilter(mouseFilter)

        # the tracker rectangle
        self.tracker = MovableGraphicsRectItem(lambda pos: self.v2.setSceneRect(pos.x(), pos.y(), 100, 100))
        self.tracker.setRect(0, 0, 100, 100)
        self.v2.setSceneRect(0, 0, 100, 100)
        self.tracker.setPen(QtGui.QPen(QtCore.Qt.darkCyan))
        self.scene.addItem(self.tracker)

        self.window.show()
        self.app.exec_()

    def leaveGV(self, gv):
        if gv is self.v1:
            self.tracker.deactivate()

    def enterGV(self, gv):
        if gv is self.v1:
            self.tracker.activate()





TestClass()