Muting streams in Android

Question

I've built a small app that mutes/unmute the music stream using the class AudioManager. In fact, it works until I close the application. i.e. I've muted the sream, I close the app, I restart the app and the button doesn't unmute the stream any more. I've searched in the net but no one seems to have met this problem.

Here's my code:

public class ControlloVolume extends Activity {
ToggleButton tb_mute;
Button btn_mute;
AudioManager mAudioManager;
boolean mute;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_controllo_volume);

    tb_mute = (ToggleButton) findViewById(R.id.tb_mute);
    btn_mute = (Button) findViewById(R.id.btn_mute);
    mAudioManager = (AudioManager)getSystemService(Context.AUDIO_SERVICE);

    if(mAudioManager.getStreamVolume(AudioManager.STREAM_MUSIC)==0){
        mute = true;
        tb_mute.setChecked(mute);
    }else{
        mute = false;
        tb_mute.setChecked(mute);
    }

    }

public void onButtonClicked(View view){
    if(!mute){
        mAudioManager.setStreamMute(AudioManager.STREAM_MUSIC, true);
        tb_mute.setChecked(true);
        mute = true;
    }else{
        mAudioManager.setStreamMute(AudioManager.STREAM_MUSIC, false);
        tb_mute.setChecked(false);
        mute = false;
    }
}

Answer 1

First, beware it's not recommended

For a better user experience, applications MUST unmute a muted stream in onPause() and mute it again in onResume() if appropriate.

But I assume you know what you're doing, so here we go.

Note this line from the docs on setStreamMute

The mute command is protected against client process death: if a process with an active mute request on a stream dies, this stream will be unmuted automatically.

I've checked on my device and indeed, when I just exit my activity, stream stays muted. But as soon as I kill the process, mute goes away. Take a look at activity lifecycle.

As your current approach will not work reliably, you could write a foreground service which will trigger the mute - start that service from your activity. Also you would likely need to setStreamSolo.

Two important things.

1. Volume==0 and muted are NOT the same thing. I.e. stream can have volume==0 but be not muted. Though if stream is muted, volume will always be 0
2. mute requests are cumulative. I.e. if you've set mute twice, you must unmute twice as well - your code doesn't handle that

As a side note, for such app you would probably want to use widget instead of activity.

---

Off topic. It seems surprisingly lot of people don't quite get how booleans work. And as I see code such as yours regulary, here is a bit streamlined rewrite.

@Override
public void onCreate(Bundle savedInstanceState) {
    // ... setup just like you did

    // boolean is just like any other type. You can assign not only
    // constants, but expressions too
    mute = (mAudioManager.getStreamVolume(AudioManager.STREAM_MUSIC)==0);
    tb_mute.setChecked(mute);
}

public void onButtonClicked(View view){
    mute = !mute; // invert value
    mAudioManager.setStreamMute(AudioManager.STREAM_MUSIC, mute);
    tb_mute.setChecked(mute);
}