RFR: 8279640: ListView with null SelectionModel/FocusModel throws NPE

[Andy Goryachev]

On Thu, 4 Aug 2022 21:29:49 GMT, Kevin Rushforth <kcr at openjdk.org> wrote:

>> This PR fixes a bunch of NPEs when a null `SelectionModel` or `FocusModel` is set on a `ListView`.
>> 
>> The following NPEs are fixed (all are also covered by exactly one test case):
>> NPEs with null selection model:
>> - Mouse click on a `ListCell`
>> - SPACE key press
>> - KP_UP (arrow up) key press
>> - HOME key press
>> - END key press
>> - BACK_SLASH + CTRL key press
>> 
>> NPEs with null focus model:
>> - SPACE key press
>> - Select an items: getSelectionModel().select(1)
>> - Clear-Select an item and add one after: listView.getSelectionModel().clearAndSelect(1); listView.getItems().add("3");
>
> I'd like to see this get resolved for JavaFX 20. I note there is a similar issue with `TableView`, which is tracked by [JDK-8187145](https://bugs.openjdk.org/browse/JDK-8187145).
> 
> As I mentioned in that JBS issue, I tend to agree that if we were starting today with a blank sheet of paper, we might have disallowed null and defined a "noop" selection model and/or focus model. At this point, though, it would be a breaking change, even though we don't specify the behavior of null, so we ought to make it work in those places where it doesn't.
> 
>> So there is no consistent behaviour for this, but a lot of code already handles null by behaving in some kind of default way without changing the property directly, and I think it might be the best to adapt to this.
> 
> This seems like the best way forward to me, but let's see what comes out of the review.
> 
> As part of this, we should clarify the spec that a null selection (and focus) model is allowed, and say what it does. This might mean a CSR, but I'd want to look at the current docs first.

Setting selection model to null (i.e. disabling selection) is a fairly frequent operation, @kevinrushforth .
The code must support that.  So no CSR is needed, I think.

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PR: https://git.openjdk.org/jfx/pull/711