Question

On UI I have a TextBox. I want to show Tree element when user clicks on TextBox. I want to prevent user from direct input text to TextBox (it’s value must depend which item user select from Tree)

Answer 1

Set ReadOnly attribute for your textbox, and for your tree widget addSelectionHandler

tree.addSelectionHandler(new SelectionHandler<TreeItem>() {
        public void onSelection(SelectionEvent<TreeItem> event) {
                  textbox.setText(event.getSelectedItem().getText()); 
        }
  });