RFR: 8334593: Adding, removing and then adding a JFXPanel again leads to NullPointerException [v3]

[Marius Hanl]

On Mon, 1 Jul 2024 09:16:52 GMT, Prasanta Sadhukhan <psadhukhan at openjdk.org> wrote:

>> Adding, then removing, and then adding a JFXPanel to the same component in the Swing scene graph leads to a NullPointerException in GlassScene because the sceneState is null.
>> Removing JFXPanel calls JFXPanel.removeNotify which calls Window.hide which calls SceneHelper.disposePeer -> Scene.disposePeer -> EmbeddedScene.dispose -> GlassScene.dispose which sets "sceneState" to null...
>> so when GlassScene.updateSceneState is called, it results in NPE.
>> Fix is to check if `host` (which is usually javafx.embed.swing.JFXPanel$HostContainer for active JFXPanel) has been reset/deleted which is done when `EmbeddedScene.dispose` is called during removeNotify and abstain from updating the scene state
>
> Prasanta Sadhukhan has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Test fix

tests/system/src/test/java/test/javafx/embed/swing/JFXPanelNPETest.java line 106:

> 104:                 frame.remove(fxPanel);
> 105:                 // fxPanel added to frame again
> 106:                 frame.add(fxPanel); // <-- leads to NullPointerException

You can use JUnit5 to write this test (class) and use `assertDoesNotThrow(() -> frame.add(fxPanel));`, which makes this a bit better to understand

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PR Review Comment: https://git.openjdk.org/jfx/pull/1493#discussion_r1661580655