RFR: 7093691: Nimbus LAF: disabled JComboBox using renderer has bad font color [v4]

[Prasanta Sadhukhan]

On Mon, 6 Feb 2023 19:04:07 GMT, Damon Nguyen <dnguyen at openjdk.org> wrote:

>> Before the fix, a JComboBox in Nimbus L&F would have normal black text even when the JComboBox was disabled if SynthComboBoxRenderer was replaced with a DefaultListCellRenderer. This text should be greyed out like in other L&F's. When looking into the defaults for Nimbus L&F files for attributes and states of a JComboBox, it confirm that the intention for disabled JComboBoxes is nimbusDisabledText (which is grey text).
>> 
>> SynthComboBoxes have an additional check in its default SynthComboBoxRenderer that enables/disables the renderer itself. The SynthComboBoxRenderer inherits its enabled state from the parent ComboBox. Since the renderer with DefaultListCellRenderer is in a separate class without a reference to the comboBox, a listener was added to SynthComboBoxUI.
>> 
>> An additional issue occurred in DefaultListCellRenderer because the renderer overrode the listener's re-assigned enabled state. In testing, setting the enabled state in DefaultListCellRenderer is redundant for all L&F's and is not needed here. However, instead of removing it altogether, a conditional was added specifically to allow ComboBoxes to skip setting enabled state here.
>> 
>> After the fix, the Nimbus JComboBox with DLCR set matches the appearance of a normal Nimbus JComboBox. I can enable/disable the JComboBoxes in the test, and the UI elements behave and appear as expected.
>
> Damon Nguyen has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Remove unused var. Fix try catch

https://github.com/openjdk/jdk/blob/master/src/java.desktop/share/classes/javax/swing/plaf/synth/SynthComboBoxUI.java#L552-L558
The present code SynthComboBoxRenderer  does enable/disable the listcell renderer based on comboBox status, why it is not working? why do we need to use a listener for DefaultListCellRenderer?

Also, I think it will be better to make the test automated..something like draw comboBox content into BufferedImage and pixel compare if it is same for disabled/enabled and fail if they are same

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PR: https://git.openjdk.org/jdk/pull/12390