Event System

The event system in Gaphor provides an API to handle events and to subscribe to events.

In Gaphor we manage event handler subscriptions through the EventManager service. Gaphor is highly event driven:

  • Changes in the loaded model are emitted as events

  • Changes on diagrams are emitted as events

  • Changes in the UI are emitted as events

Although Gaphor depends heavily on GTK for its user interface, Gaphor is using its own event dispatcher. Events can be structured in hierarchies. For example, an AttributeUpdated event is a subtype of ElementUpdated. If we are interested in all changes to elements, we can also register ElementUpdated and receive all AttributeUpdated events as well.

class gaphor.core.eventmanager.EventManager[source]

The Event Manager.

handle(*events: object) None[source]

Send event notifications to registered handlers.

priority_subscribe(handler: Callable[[object], None]) None[source]

Register a handler.

Priority handlers are executed directly. They should not raise other events, cause that can cause a problem in the exection order.

It’s basically to make sure that all events are recorded by the undo manager.

shutdown() None[source]

Shutdown the services, free resources.

subscribe(handler: Callable[[object], None]) None[source]

Register a handler.

Handlers are triggered (executed) when specific events are emitted through the handle() method.

unsubscribe(handler: Callable[[object], None]) None[source]

Unregister a previously registered handler.

Under the hood events are handled by the Generics library. For more information about how the Generic library handles events see the Generic documentation.