RFR: 6672644: JComboBox still scrolling if switch to another window and return back

[Damon Nguyen]

On Wed, 4 Sep 2024 07:52:08 GMT, Abhishek Kumar <abhiscxk at openjdk.org> wrote:

>> In a JComboBox, if the user opens the dropdown list and clicks and holds the down-button, then ALT-TABs to switch focus, when the user re-focuses the frame with the JComboBox and opens the dropdown list again, the list will still be scrolling even though the down-button isn't pressed.
>> 
>> This isn't OS or L&F specific, although Aqua L&F does not have any directional arrows in the dropdown list (and is thus exempt). This led me to believe it could be handled in BasicComboBoxUI where focusLost and focusGain are used or isPopupVisible but the scroll behavior cannot be altered here. Likewise for BasicComboPopup where `autoscroll` is used. However, this behavior isn't related to autoscroll and is actually found in the JScrollbar of the JScrollpane inside of the JComboBox. The timer for the scroll action starts but is never stopped if focus is lost, so a new listener is created and used. The proposed solution uses `KeyboardFocusManager` to track the focus owner. The listener stops the `scrollTimer` when the `focusOwner` property is changed. With this change, the list no longer automatically scrolls when re-focused and instead opens normally.
>> 
>> The included test is manual due to the need to confirm that the list still scrolls after ALT-TABing. The L&F is set to Metal since it is the cross-platform lookandfeel and has directional buttons for the JScrollPane list.
>
> I can verify on linux machine that it is suto-scrolling but it is intermittent on windows as well as on linux. Sometimes the list is scrolling and sometimes it's not. Are you facing the same?
> To regain focus, if click on frame title bar then the intermittent issue can be observed.

@kumarabhi006 Tested with the additional changes I made. Looks like it's working now. No other tests are failing in CI with the changes either. Can you check it out again?

-------------

PR Comment: https://git.openjdk.org/jdk/pull/20845#issuecomment-2458263614