GraphicsItem.py 文件源码

def getViewBox(self):
        """
        Return the first ViewBox or GraphicsView which bounds this item's visible space.
        If this item is not contained within a ViewBox, then the GraphicsView is returned.
        If the item is contained inside nested ViewBoxes, then the inner-most ViewBox is returned.
        The result is cached; clear the cache with forgetViewBox()
        """
        if self._viewBox is None:
            p = self
            while True:
                try:
                    p = p.parentItem()
                except RuntimeError:  ## sometimes happens as items are being removed from a scene and collected.
                    return None
                if p is None:
                    vb = self.getViewWidget()
                    if vb is None:
                        return None
                    else:
                        self._viewBox = weakref.ref(vb)
                        break
                if hasattr(p, 'implements') and p.implements('ViewBox'):
                    self._viewBox = weakref.ref(p)
                    break
        return self._viewBox()  ## If we made it this far, _viewBox is definitely not None