RFR: 6672644: JComboBox still scrolling if switch to another window and return back [v6]

[Abhishek Kumar]

On Wed, 20 Nov 2024 07:20:05 GMT, Damon Nguyen <dnguyen 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.
>
> Damon Nguyen has updated the pull request incrementally with one additional commit since the last revision:
> 
>   isPressed check and set

src/java.desktop/share/classes/javax/swing/plaf/basic/BasicScrollBarUI.java line 1224:

> 1222:      * A listener to listen for keyboard focus changes.
> 1223:      */
> 1224:     protected class KeyboardFocusListener extends MouseAdapter implements PropertyChangeListener {

Why do you extends "MouseAdapter" ?
Is it really needed ?

test/jdk/javax/swing/JComboBox/JComboBoxScrollFocusTest.java line 56:

> 54:                 .title("JComboBoxScrollFocusTest Test Instructions")
> 55:                 .instructions(INSTRUCTIONS)
> 56:                 .rows((int) INSTRUCTIONS.lines().count() + 2)

not required anymore.

test/jdk/javax/swing/JComboBox/JComboBoxScrollFocusTest.java line 65:

> 63:     private static JFrame createAndShowGUI() {
> 64:         JFrame frame = new JFrame("JComboBoxScrollFocusTest Test Frame");
> 65:         JComboBox combobox = new JComboBox();

Suggestion:

        JComboBox<String> combobox = new JComboBox<>();

test/jdk/javax/swing/JComboBox/JComboBoxScrollFocusTest.java line 66:

> 64:         JFrame frame = new JFrame("JComboBoxScrollFocusTest Test Frame");
> 65:         JComboBox combobox = new JComboBox();
> 66:         for (int i = 0; i < 100; i ++) {

Suggestion:

        for (int i = 0; i < 100; i++) {

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PR Review Comment: https://git.openjdk.org/jdk/pull/20845#discussion_r1851869858
PR Review Comment: https://git.openjdk.org/jdk/pull/20845#discussion_r1851871991
PR Review Comment: https://git.openjdk.org/jdk/pull/20845#discussion_r1851881030
PR Review Comment: https://git.openjdk.org/jdk/pull/20845#discussion_r1851881797