RFR: 8354813: Parent.isNeedsLayout() may return wrong value in property listener

[Michael Strauß]

On Wed, 16 Apr 2025 17:05:55 GMT, Andy Goryachev <angorya at openjdk.org> wrote:

>> A listener that is added to `Parent.needsLayoutProperty()` may see a wrong value when calling `Parent.isNeedsLayout()` from the callback. The fix is to apply the value before notifying the listeners.
>
> modules/javafx.graphics/src/main/java/javafx/scene/Parent.java line 996:
> 
>> 994:         // Needs to be set before needsLayout is updated, as otherwise a listener that
>> 995:         // calls isNeedsLayout() might see the old value.
>> 996:         layoutFlag = flag;
> 
> This is the right change, but I suspect it might cause regression.
> 
> The JavaFX entities which call `isNeedsLayout()`:
> 
> `VirtualFlow::layoutChildren`
> `VirtualFlow::setCellIndex`
> 
> We may need to focus on List/Table/Tree/TableViews during testing.
> 
> (Anecdata: I've seen continuous layout calls in the TableView before)

It's very unlikely to cause regressions, because `needsLayoutProperty()` is not used anywhere in JavaFX. The only thing that is different now is that a listener added to this property will see the correct value when calling `isNeedsLayout()`.

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PR Review Comment: https://git.openjdk.org/jfx/pull/1781#discussion_r2047484643