Hello,

I am trying to get a list of audio track info from an Android device. On the Java side, this is accomplished with a static getMusic() method, which returns List<AudioTrack>. getMusic() lives in my custom AndroidDeviceMediaCollection class. AudioTrack is essentially a struct of various fields, with a toString() method. I am able to instantiate each AudioTrack that I expect to find, print it out in Java using toString(), and then add it to the list. But I am running into problems on the C++ side. In particular, it seems that I am not able to convert the returned List<AudioTrack>, which is held in a QAndroidJniObject, to a jobjectArray without destroying most of its contents! Here is the relevant C++ code:

Qt Code: 
  1. GenericModel<Album>* AndroidDeviceMediaCollection::albumsModel() {
  2. 	QPlatformNativeInterface *interface = QApplication::platformNativeInterface();
  3. 	jobject activity = (jobject) interface->nativeResourceForIntegration("QtActivity");
  4. 	QAndroidJniObject music = QAndroidJniObject::callStaticObjectMethod("org.qtproject.mythings.AndroidDeviceMediaCollection", "getMusic", "(Landroid/content/Context;)Ljava/util/List;", activity);
  5. 	Q_ASSERT_X(music.isValid(), "albumsModel", "Null QAndroidJniObject!");
  6. 	jobjectArray musicArray = music.object<jobjectArray>();
  7. 	QAndroidJniEnvironment qjniEnv;
  8. 	const int n = qjniEnv->GetArrayLength(musicArray);
  9. 	qDebug() << "Got jobjectArray of length:" << n; // prints expected value
  10. 	for (int i = 0; i < n; ++i) {
  11. 		jobject jAudioTrack = qjniEnv->GetObjectArrayElement(musicArray, i);
  12. 		if (jAudioTrack) {
  13. 			// parse, add to albums...
  14. 			qjniEnv->DeleteLocalRef(jAudioTrack);
  15. 		}
  16. 		else
  17. 			qDebug() << "Got null jAudioTrack at index:" << i; // most elements are null!
  18. 	}
  19. 	return &m_albums;
  20. }
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To be clear, I am successfully converting to a jobjectArray with exactly the right number of elements, but for most of those elements I see the null debug message.

I was just wondering if someone could point out what I am doing wrong here, or if there is a different way to acquire and iterate over a list of instances of a custom type. Any insight appreciated. Thank you!