在Output地方发现以下log:
QGraphicsItem::installSceneEventFilter: event filters can only be installed on items in a scene.
在google上查找:
Installs an event filter for this item on filterItem, causing all events for this item to first pass through filterItem's sceneEventFilter() function.
To filter another item's events, install this item as an event filter for the other item. Example:
An item can only filter events for other items in the same scene. Also, an item cannot filter its own events; instead, you can reimplement sceneEvent() directly.
Items must belong to a scene for scene event filters to be installed and used.
没理解