How to expand TreeViewer programmatically?

Question

How to expand TreeViewer programmatically?

If I use underlying Tree.setExpanded(true),

    action1 = new Action() {
        public void run() {
            viewer.getTree().getItems()[0].setExpanded(true);
        }
    };

element does not appear:

If I use mouse clicks, branch expands ok.

Answer 1

Have a look at AbsractTreeViewer#expandToLevel(Object, int):

Expands all ancestors of the given element or tree path so that the given element becomes visible in this viewer's tree control, and then expands the subtree rooted at the given element to the given level.