B4X:
Private Sub SwitchTargetPlayerView(FullScreenIsDestination As Boolean)
Dim mp As HalfScreen
mp = B4XPages.GetPage("Media Player")
Dim jo As JavaObject
Dim Player As Object = mp.Player.As(JavaObject).GetField("player") ' This line crashed!
jo.InitializeStatic("androidx.media3.ui.PlayerView")
jo.RunMethod("switchTargetView", Array(Player, IIf(FullScreenIsDestination, mp.SimpleExoPlayerView1, SimpleExoPlayerView1), IIf(FullScreenIsDestination, SimpleExoPlayerView1, mp.SimpleExoPlayerView1)))
End SubWhile testing B4A 14.20 Beta with R8 enabled, I ran into a runtime crash when using JavaObject to access fields or methods via string names (for example, getting an internal .player field or calling dynamic methods via reflection).
Because R8 is a static analyzer, it can't detect string literals passed to JavaObject, so it treats those fields/methods as unused, strips them, or obfuscates them (resulting in crashes like Field: player not found in: b0.d).
To prevent this for apps using reflection-heavy libraries (like Media3/ExoPlayer wrappers or custom Java objects), developers need to add explicit keep rules like this to their ProGuard configuration:
B4X:
-keepclassmembers class * {
*** player;
}Would it be worth adding a note or considering safer default ProGuard rules in the IDE template for common reflection patterns, so others don't hit unexpected obfuscation crashes when moving to R8?
Thanks!