public class MyDSLOutlineTreeProvider extends DefaultOutlineTreeProvider {
    def _createChildren(IOutlineNode parentNode, MyXTextGrammarRoot root) {
        // ...

        MyView.updateInput(
            root.eResource.getResourceSet().getResources().get(0)
        )
    }
//...
}

IEditorPart editor = partRef.getPage().getActiveEditor();
IXtextDocument document =
	((XtextEditor) editor).getDocument();

MyXTextGrammarRoot root =
	(MyXTextGrammarRoot) document.readOnly(
		new IUnitOfWork<XtextResource, XtextResource>() {
			public XtextResource exec(XtextResource state) {
				return state;
			}
		}
	).getContents().get(0);

System.out.println(root.eResource());

document.addModelListener(
	new IXtextModelListener() {
		@Override
		public void modelChanged(XtextResource resource) {
			System.out.println(resource);
		}
	}
);