RFR: 8190411: NPE in SliderSkin:140 if Slider.Tooltip.autohide is true [v4]

[Karthik P K]

On Mon, 5 Dec 2022 12:48:14 GMT, Karthik P K <kpk at openjdk.org> wrote:

>> Cause: When slider is dragged for first time after tooltip appears, setOnMousePressed event was not invoked, hence dragStart was null in the subsequently invoked event handler (setOnMouseDragged).
>> 
>> Fix: Initialized dragStart in initialize method.
>> 
>> Test: Added system test to validate the fix.
>> 
>> Note: Initializing dragStart in layoutChildren method as suggested in the bug was causing side effects. Hence initialized dragStart in initialize method.
>
> Karthik P K has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Update in mouse enter and exit events. Update in unit test

I do not have a touchscreen machine as well.
@aghaisas please check if bug given above is fixed.

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PR: https://git.openjdk.org/jfx/pull/965