How to react on a element selection in the diagram view?

[rsoika]

I am implementing a custom module to show extended properties for GLSP elements.

How do I react on the selection of a GSLP Element from the diagram pane? I guess I have to implement some kind of action handler?
I also would like to understand if the event of a selected element is generated directly form the diagram view or if this is going through the GLSP server first?

[rsoika]

I found the solution by myself as this topic is perfectly documented - Implementing an Action Handler (GLSP Client)
Also important was the reference to the existing Evens provided by the GLSP protocol decribing the ElementSelection

So in summary you have to implement a custom handler for the ElementSeleciton Action:

@injectable()
export class MySelectResponseActionHandler implements IActionHandler{
    handle(action: SelectAction): void | Action {
	console.log('hi selection action !');
        // implement your custom logic to handle the action
        // Optionally issue a response action
    }
}

and register this action handler in the diagram module (“di.config.ts”):

const bpmnDiagramModule = new ContainerModule((bind, unbind, isBound, rebind) => {
    ....
    configureActionHandler(context, SelectAction.KIND, MySelectResponseActionHandler);
    ......
});