* click a outside button or menu item.
*/
public void focus() {
// retrieve focus should work when spreadsheet init or after invalidate.
// so I use response to implement it.
JSONObj result = new JSONObj();
result.setData("type", "retrive");
/**
* rename zssfocus -> doRetrieveFocusCmd
*/
response("retrieveFocus" + this.getUuid(), new AuRetrieveFocus(this, result.toString()));
}