When a component is created in an event listener, it is assigned automatically to the associated desktop of the event being processed. This assignment happens even if the component is not attached to a page. It means that any component you created in an event listener can be used in the same desktop that the listener is handling.

When a component is created in a thread other than any event listener, it doesn't belong to any desktop. In this case, you could attach to any desktop you want as long as the attachment occurs in a proper event listener. Of course, once the component is attached to a desktop, it belongs to the desktop forever.

For most applications, it is rarely necessary to create components in a thread other than event listeners. However, if you have a long operation, you might want to execute it in a background thread. Then, you could prepare the component tree at the background and then add it to a desktop when a proper event is received. Refer to the Long Operations section in the Event Listening and Processing chapter.