control volume seekBar in dialog (AsyncTask)

Question

I have an AsyncTask in which the onPostExecute method is:

protected void onPostExecute(String args) {


            final AudioManager audioManager = (AudioManager)getSystemService(Context.AUDIO_SERVICE);
            int maxVolume = audioManager.getStreamMaxVolume(AudioManager.STREAM_MUSIC);
            int curVolume = audioManager.getStreamVolume(AudioManager.STREAM_MUSIC);

            LayoutInflater inflater = (LayoutInflater) getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            View layout = inflater.inflate(R.layout.custom_dialog, (ViewGroup) findViewById(R.id.dialog_root_element));


            AlertDialog.Builder builder = new AlertDialog.Builder(Main.this);
            builder.setView(layout)
                    .setMessage(name)
                    .setTitle("playing...")
                    .setCancelable(false)
                    .setNeutralButton("stop/volver",
                            new DialogInterface.OnClickListener() {
                                public void onClick(DialogInterface dialog,
                                        int id) {
                                    mediaPlayer.stop();
                                    dialog.cancel();
                                }
                            });
            alert = builder.create();

            alert.show();

            SeekBar volControl = (SeekBar)findViewById(R.id.dialog_seekbar);
            volControl.setMax(maxVolume);
            volControl.setProgress(curVolume);
            volControl.setOnSeekBarChangeListener(new SeekBar.OnSeekBarChangeListener() {
                @Override
                public void onStopTrackingTouch(SeekBar arg0) {
                }

                @Override
                public void onStartTrackingTouch(SeekBar arg0) {
                }

                @Override
                public void onProgressChanged(SeekBar arg0, int arg1, boolean arg2) {
                    audioManager.setStreamVolume(AudioManager.STREAM_MUSIC, arg1, 0);
                }
            });


            mediaPlayer.setOnCompletionListener(new OnCompletionListener() {
                public void onCompletion(MediaPlayer mp) {
                    mediaPlayer.stop();
                    alert.dismiss();
                }
            });

            // updating UI from Background Thread
            runOnUiThread(new Runnable() {
                public void run() {
                }
            });

        }

the error is in:

volControl.setMax(maxVolume);

but I don't understand why... (In debug mode, maxVolume is 15)

I am trying do a dialog with a volume control seekBar but I don't see the error. can I modify the volume of a sound wit AsyncTask?

thanks a lot!

Answer 1

You're calling findViewById on the wrong object. The code is looking for your SeekBar in your activity's layout file, which probably doesn't exist (I'm guessing you're getting a null pointer exception).

Try this, show your dialog, then call findViewById on the dialog, not the activity to find your SeekBar.

alert.show();
SeekBar volControl = (SeekBar)alert.findViewById(R.id.dialog_seekbar);

The important part here is alert.findViewById().