Why does the mediaplayer.prepareAsync() throw an IllegalStateException?

Question

Here is my Activity:

public class AlarmPlayerActivity extends AppCompatActivity implements MediaPlayer.OnPreparedListener {
    private MediaPlayer player;

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_alarm_player);
        int alarm_number = getIntent().getIntExtra(Config.KEY_ALARM_NO, 0);
        ((TextView) findViewById(R.id.alarm_message)).setText(getString(R.string.alarms_was_set).concat(": " + alarm_number));
    }

    public void stopPlayingAlarm(View view) {
        if (player != null && player.isPlaying()) {
            player.reset();
            player.stop();
            player.release();
        }
    }

    @Override
    protected void onStart() {
        super.onStart();
        Uri uri = RingtoneManager.getDefaultUri(RingtoneManager.TYPE_ALARM);
        player = MediaPlayer.create(this, uri);
        player.setAudioStreamType(AudioManager.STREAM_ALARM);
        player.setLooping(true);
        player.setOnPreparedListener(this);
        player.prepareAsync();
    }

    @Override
    public void onPrepared(MediaPlayer mp) {
        mp.start();
    }
}

But it throws IllegalStateException on player.prepareAsync() call.

I cannot fix it although I have tried other answers found in this site.

Note that, this activity is launched from a broadcast receiver which is triggered by an RTC_WAKEUP alarm.

Here is part of my AndroidManifest :

    <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
    <uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
    <uses-permission android:name="android.permission.CHANGE_WIFI_STATE" />
    <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED" />
    <uses-permission android:name="android.permission.EXPAND_STATUS_BAR" />
    <uses-permission android:name="com.android.alarm.permission.SET_ALARM" />
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
    <uses-permission android:name="com.google.android.c2dm.permission.RECEIVE" />
    <uses-permission android:name="android.permission.FOREGROUND_SERVICE" />
    <uses-permission android:name="android.permission.MODIFY_AUDIO_SETTINGS"/>

Answer 1

MediaPlayer already had prepare() inside. So if you call a second prepare(), it will throw exception.

Link official doc