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

["Kamil (JIRA)" <ji...@apache.org>]

Kamil created WICKET-6403:
-----------------------------

             Summary: DropDownChoice ignores OnChangeAjaxBehavior while setting null value when required is true
                 Key: WICKET-6403
                 URL: https://issues.apache.org/jira/browse/WICKET-6403
             Project: Wicket
          Issue Type: Bug
    Affects Versions: 8.0.0-M6
            Reporter: Kamil


I have a simple DropDown with OnChangeAjaxBehavior:
{code}
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);
{code}

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

Now when instead of:
{code}
add(wicketDropDown);
{code}
I set:
{code}
add(wicketDropDown.setRequired(true));
{code}
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).



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