public class NewPartHandler {

	private static final String ID_WINDOW = "de.emsw.test.e4.multiwindow.trimmedwindow.second";
	private static final String ID_STACK = "de.emsw.test.e4.multiwindow.partstack.second";
	private static final String ID_PART_PREFIX = "de.emsw.test.e4.multiwindow.part.";

	private int partCnt = 0;

	@Execute
	public void execute(EModelService modelService, MApplication app, EPartService partService) {
				
		// Check if the Part already exists
		MPartStack stack = (MPartStack)modelService.find(ID_STACK, app);
		if (stack == null) { // and create it if not
			stack = modelService.createModelElement(MPartStack.class);
			stack.setElementId(ID_STACK);
			
			// Find the Default-Window to place the Part
			MWindow window = (MWindow)modelService.find(ID_WINDOW, app);
			if (window == null) { // and create it if it doesn't exist  (expected)
				window = modelService.createModelElement(MTrimmedWindow.class);
				window.setElementId(ID_WINDOW);
				window.setLabel("Second Window");
				window.getPersistedState().put(IPresentationEngine.STYLE_OVERRIDE_KEY, "" + SWT.SHELL_TRIM);
				
				app.getChildren().add(window); // Add window to application
			}
			
			window.getChildren().add(0, stack); // Add stack to the window
		}

		// Create a new Part
		partCnt++;
		MPart part = modelService.createModelElement(MPart.class);
		part.setElementId(ID_PART_PREFIX + partCnt);
		part.setContributionURI("bundleclass://de.emsw.test.e4.multiWindow/de.emsw.test.e4.multiWindow.parts.NewPart");
		part.setCloseable(true);
		part.setLabel("Part " + partCnt);
		part.getTags().add(EPartService.REMOVE_ON_HIDE_TAG);
		
		stack.getChildren().add(part); // Add part to stack
		partService.showPart(part, PartState.ACTIVATE); // Show part
	}
}

private boolean isInContainer(MUIElement element) {
	if (modelService.isHostedElement(element, getWindow()))
		return true;
	List<MUIElement> allPerspectiveElements = modelService.findElements(workbenchWindow, null,
			MUIElement.class, null, EModelService.PRESENTATION);
	return allPerspectiveElements.contains(element);
}

private MWindow getWindow() {
	if (workbenchWindow != null)
		return workbenchWindow;
	if (application.getSelectedElement() != null)
		return application.getSelectedElement();
	List<MWindow> windows = application.getChildren();
	if (windows.size() != 0)
		return windows.get(0);
	return null;
}

EPartService appPartService = app.getContext().get(EPartService.class);
appPartService.showPart(part, PartState.ACTIVATE); // Show part