Undo/Redo context

[dejawho]

Hi,, I'm struggling into contribute an undo/redo action for my editor in theia. I'm able to attach to the actions and provide an handler for the undo/redo using the CommandRegistry.registerHandler, and it seems to works.
But I have some doubts about the context, eg if I open a monaco editor and do the undo then it will be always resolved by my handler, also the isEnabled on my handler doesn't help me since the args are empty so I can't enable it selectively.
I'm not even sure that in theia there is the concept of focused editor/extension, since more stuff can be opened at once, but just in case is there a built-in way to get which is the active editor/widget/extension?

[kittaakos]

even sure that in theia there is the concept of focused editor

The application shell exposes the following:

theia/packages/core/src/browser/shell/application-shell.ts

Lines 853 to 871 in 6ef0867

	/**
	* The current widget in the application shell. The current widget is the last widget that
	* was active and not yet closed. See the remarks to `activeWidget` on what _active_ means.
	*/
	get currentWidget(): Widget | undefined {
	return this.tracker.currentWidget || undefined;
	}
	/**
	* The active widget in the application shell. The active widget is the one that has focus
	* (either the widget itself or any of its contents).
	*
	* _Note:_ Focus is taken by a widget through the `onActivateRequest` method. It is up to the
	* widget implementation which DOM element will get the focus. The default implementation
	* does not take any focus; in that case the widget is never returned by this property.
	*/
	get activeWidget(): Widget | undefined {
	return this.tracker.activeWidget || undefined;
	}

There is a slight difference in the monaco editor; a monaco editor can be active but not focused (the cursor does not blink in the editor, but the editor's tab is marked as the active one).

You can check how the VS Code-based editor actions are handled in Theia here:

theia/packages/monaco/src/browser/monaco-command.ts

Lines 163 to 171 in 6ef0867

	const editor = codeEditorService.getFocusedCodeEditor() || codeEditorService.getActiveCodeEditor();
	if (editorActions.has(id)) {
	const action = editor && editor.getAction(id);
	return !!action && action.isSupported();
	}
	if (!!editorRegistry.getEditorCommand(id)) {
	return !!editor;
	}
	return true;

As always, if you could provide a stripped-down example that does not work, we could improve Theia.

You could also look into the selection service, maybe that helps a bit.