[WICKET-6403] DropDownChoice ignores OnChangeAjaxBehavior while setting null value when required is true

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Invalid
• Affects Version/s: 8.0.0-M6
• Assignee: Sven Meier
• Reporter: Kamil
• Created: 19/Jun/17 13:33
• Updated: 21/Jun/17 17:36
• Resolved: 21/Jun/17 17:36

Description

I have a simple DropDown with OnChangeAjaxBehavior:

List<String> choices = Arrays.asList("one", "two", "three");
IModel<String> wicketModel = Model.of();
DropDownChoice<String> wicketDropDown = new DropDownChoice<>("wicketDropDown",wicketModel , ListModel.of(choices));
wicketDropDown.add(new OnChangeAjaxBehavior() {
	@Override
	protected void onUpdate(AjaxRequestTarget target) {
		System.out.println("Wicket change: "+wicketModel.getObject());
	}
});
add(wicketDropDown);

onUpdate is called everytime I change the value even if this value is "null value".

Now when instead of:

add(wicketDropDown);

I set:

add(wicketDropDown.setRequired(true));

onUpdate works on selecting values but does not work when selecting "null value" which is wrong.
One of the use cases why it is wrong: I have two dropdowns. First dropdown selects Group and second selects Subgroup. Subgroup can not be selected if Group is null, though if I select Group, then I select Subgroup and then clear the Group - Subgroup should be cleared as well (but I'm not able to do that because onUpdate is not being called).