[audiofileplayer] NullPointerException

[ozzy1873]

First of all, very nice control with clean source code and GREAT comments! Thanks!

There is a corner case that throws an NPE. Steps to recreate:

1. Try to load a remote file that is corrupted so that load fails.
2. Handle the onError callback and dispose the audio control inside the callback.
3. Without doing anything else, let the phone go to sleep.
4. The following exception occurs:

I/AudiofileplayerPlugin(26650): onMethodCall: method = load
V/MediaHTTPService(26650): MediaHTTPService(android.media.MediaHTTPService@3cb2af9): Cookies: null
I/AudiofileplayerPlugin(26650): onMethodCall: method = setVolume
V/MediaHTTPService(26650): makeHTTPConnection: CookieManager created: java.net.CookieManager@a2f5a3e
V/MediaHTTPService(26650): makeHTTPConnection(android.media.MediaHTTPService@3cb2af9): cookieHandler: java.net.CookieManager@a2f5a3e Cookies: null
I/AudiofileplayerPlugin(26650): onMethodCall: method = play
E/MediaPlayerNative(26650): error (1, -2147483648)
E/MediaPlayer(26650): Error (1,-2147483648)
E/ManagedMediaPlayer(26650): onError: what:1 extra: -2147483648
I/flutter (26650): OnError called
I/flutter (26650): audio dispose called without awaiting

=== Everything looks good until the phone goes to sleep, then... ===

I/AudiofileplayerPlugin(26650): onMethodCall: method = pause
E/MethodChannel#audiofileplayer(26650): Failed to handle method call
E/MethodChannel#audiofileplayer(26650): java.lang.NullPointerException: Attempt to invoke virtual method 'void com.google.flutter.plugins.audiofileplayer.ManagedMediaPlayer.pause()' on a null object reference
E/MethodChannel#audiofileplayer(26650): at com.google.flutter.plugins.audiofileplayer.AudiofileplayerPlugin.onMethodCall(AudiofileplayerPlugin.java:107)
E/MethodChannel#audiofileplayer(26650): at io.flutter.plugin.common.MethodChannel$IncomingMethodCallHandler.onMessage(MethodChannel.java:222)
E/MethodChannel#audiofileplayer(26650): at io.flutter.embedding.engine.dart.DartMessenger.handleMessageFromDart(DartMessenger.java:96)
E/MethodChannel#audiofileplayer(26650): at io.flutter.embedding.engine.FlutterJNI.handlePlatformMessage(FlutterJNI.java:656)
E/MethodChannel#audiofileplayer(26650): at android.os.MessageQueue.nativePollOnce(Native Method)
E/MethodChannel#audiofileplayer(26650): at android.os.MessageQueue.next(MessageQueue.java:336)
E/MethodChannel#audiofileplayer(26650): at android.os.Looper.loop(Looper.java:174)
E/MethodChannel#audiofileplayer(26650): at android.app.ActivityThread.main(ActivityThread.java:7356)
E/MethodChannel#audiofileplayer(26650): at java.lang.reflect.Method.invoke(Native Method)
E/MethodChannel#audiofileplayer(26650): at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
E/MethodChannel#audiofileplayer(26650): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)
E/DartMessenger(26650): Uncaught exception in binary message listener
E/DartMessenger(26650): java.lang.IllegalStateException: Reply already submitted
E/DartMessenger(26650): at io.flutter.embedding.engine.dart.DartMessenger$Reply.reply(DartMessenger.java:151)
E/DartMessenger(26650): at io.flutter.plugin.common.MethodChannel$IncomingMethodCallHandler.onMessage(MethodChannel.java:240)
E/DartMessenger(26650): at io.flutter.embedding.engine.dart.DartMessenger.handleMessageFromDart(DartMessenger.java:96)
E/DartMessenger(26650): at io.flutter.embedding.engine.FlutterJNI.handlePlatformMessage(FlutterJNI.java:656)
E/DartMessenger(26650): at android.os.MessageQueue.nativePollOnce(Native Method)
E/DartMessenger(26650): at android.os.MessageQueue.next(MessageQueue.java:336)
E/DartMessenger(26650): at android.os.Looper.loop(Looper.java:174)
E/DartMessenger(26650): at android.app.ActivityThread.main(ActivityThread.java:7356)
E/DartMessenger(26650): at java.lang.reflect.Method.invoke(Native Method)
E/DartMessenger(26650): at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
E/DartMessenger(26650): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)

[monkeyswarm]

I get similar behavior when I turn off the mobile device's wifi and start the example app. The example app attempts to load a remote URL, and if it fails, it attempts to dispose itself (calling release). Log snippet below.

Looks like load failures (which yield a null MediaPlayer instance) need to be guarded against in all other calls. This will stop the NPEs, but could still yield unusual behavior for the developer (who has a valid Audio instance in the Dart code, but which has no underlying MediaPlayer, and all method calls will effectively be dropped.)

=====
I/AudiofileplayerPlugin(17781): onMethodCall: method = release
E/MethodChannel#audiofileplayer(17781): Failed to handle method call
E/MethodChannel#audiofileplayer(17781): java.lang.NullPointerException: Attempt to invoke virtual method 'void com.google.flutter.plugins.audiofileplayer.ManagedMediaPlayer.release()' on a null object reference
E/MethodChannel#audiofileplayer(17781): at com.google.flutter.plugins.audiofileplayer.AudiofileplayerPlugin.onMethodCall(AudiofileplayerPlugin.java:88)