Events¶

The framework has its own event system for what happens inside the scene, and avoids pyqtSignal for it. You subscribe to an event by registering a callback:

scene.addHasBeenModifiedListener(callback)

Callbacks take no arguments and can be registered at any time. The classes that emit events list them at the top of their documentation.

Scene events¶

Listener	Fired when
`addHasBeenModifiedListener`	something in the scene has changed
`addItemSelectedListener`	a node or an edge is selected
`addItemsDeselectedListener`	the selection is cleared
`addDragEnterListener`	something is dragged onto the scene; the callback may allow or deny the drag
`addDropListener`	something is dropped into the scene

scene.addHasBeenModifiedListener(lambda: print("the graph changed"))

History events¶

SceneHistory reports what the undo/redo stack is doing:

Listener	Fired when
`addHistoryModifiedListener`	a history stamp has been stored or restored
`addHistoryStoredListener`	a history stamp has been stored
`addHistoryRestoredListener`	a history stamp has been restored

The history listeners can also be removed again, which is handy when a dialog or a temporary widget subscribes and then goes away:

scene.history.addHistoryStoredListener(on_stored)
scene.history.removeHistoryStoredListener(on_stored)