Popup AlertDialog with a seekBar to change app volume

Question

I am new to Android and I need to create an AlertDialog when I press an specific button. AlertDialog has a Seekbar and the seekBar is used to change the volume for my application. But I cannot make it work. Can you please help me? Thank you.

I get this error :

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.SeekBar.setMax(int)' on a null object reference

and my code looks like this:

public class Setting extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_setting);
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);
    getSupportActionBar().setDisplayHomeAsUpEnabled(true);
    }

    public AlertDialog AlarmVolume(View view) {

        /*
    This part of code creates a dialog which has a seekbar for volume.
     */
    AlertDialog.Builder builder = new AlertDialog.Builder(this);
    LayoutInflater inflater = (LayoutInflater) getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    View v = inflater.inflate(R.layout.volume_dialog, (ViewGroup) findViewById(R.id.settingsItem));
    builder.setView(v).setTitle("Adjust Alarm Volume").setPositiveButton("OK", new DialogInterface.OnClickListener() {
        @Override
        public void onClick(DialogInterface dialog, int which) {
            //TODO save new volume amount
        }
    }).setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
        @Override
        public void onClick(DialogInterface dialog, int which) {
        }
    });

    SeekBar seekbarVolume = (SeekBar)findViewById(R.id.volumeSeekBar);
    final AudioManager audioManager = (AudioManager)getSystemService(Context.AUDIO_SERVICE);
    seekbarVolume.setMax(audioManager.getStreamMaxVolume(AudioManager.STREAM_ALARM));
    seekbarVolume.setProgress(audioManager.getStreamVolume(AudioManager.STREAM_ALARM));

    seekbarVolume.setOnSeekBarChangeListener(new SeekBar.OnSeekBarChangeListener() {     

        @Override
        public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) {
            audioManager.setStreamVolume(AudioManager.STREAM_ALARM, progress, 0);
        }
    });
    return  builder.create();
    }
}

and this is my volum_dialog.xml file:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent">

<SeekBar
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/volumeSeekBar"
    android:layout_marginTop="15sp"
    android:layout_weight="1" />
</LinearLayout>

Answer 1

You are trying to find your seekbar in your contextView (R.layout.activity_setting):

 SeekBar seekbarVolume = (SeekBar)findViewById(R.id.volumeSeekBar);

It returns null because you created your SeekBar dynamically for your AlertDialog:

View v = inflater.inflate(R.layout.volume_dialog, (ViewGroup) findViewById(R.id.settingsItem));

To solve this issue, change this line (SeekBar)findViewById(R.id.volumeSeekBar); to:

(SeekBar) v.findViewById(R.id.volumeSeekBar);

It tries to find your Seekbar in View v instead of ContextView which should work fine.