For a musical application (a sequencer), I have a few buttons

static ArrayList<Button> Buttonlist = new  ArrayList<Button>(); 

    Buttonlist.add(0,(Button) findViewById(R.id.case_kick1));
    Buttonlist.add(1,(Button) findViewById(R.id.case_kick2));
    Buttonlist.add(2,(Button) findViewById(R.id.case_kick3));
    Buttonlist.add(3,(Button) findViewById(R.id.case_kick4));
    Buttonlist.add(4,(Button) findViewById(R.id.case_kick5));
    Buttonlist.add(5,(Button) findViewById(R.id.case_kick6));
    Buttonlist.add(6,(Button) findViewById(R.id.case_kick7));
    Buttonlist.add(7,(Button) findViewById(R.id.case_kick8)); 

that I activate through onClickListeners with for example

Buttonlist.get(0).setActivated(true);

I played the activated sound via a loop and ifs :

if (Buttonlist.get(k).isActivated()) {mSoundManager.playSound(1); Thread.sleep(250);}

The app played fine but I couldn't access the play/pause button when it was playing : I searched and found out about AsyncTasks.

I have a nested class PlayPause :

class PlayPause extends AsyncTask<ArrayList<Button>,Integer,Void>

in which I have this :

protected Void doInBackground(ArrayList<Button>... params) {

    for(int k=0;k<8;k++)
    {
    boolean isPlayed = false;

    if (Buttonlist.get(k).isActivated()) {
    mSoundManager.playSound(1); 
    isPlayed = true;
    try {Thread.sleep(250);
    } 
    catch (InterruptedException e) 
    {e.printStackTrace();}}

    if(!isPlayed){
    try {Thread.sleep(250);}
    catch (InterruptedException e) 
    {e.printStackTrace();}
    }

   }
 return null;

}

I launch it via

   Play.setOnClickListener(new PlayClickListener());

with PlayClickListener :

public class PlayClickListener implements OnClickListener {

private Tutorial acti;


public PlayClickListener(){
    super();
    }

    @SuppressWarnings("unchecked")
    public void onClick(View v) {
    if(Tutorial.play==0){
        Tutorial.play=1;
        Tutorial.Play.setBackgroundResource(R.drawable.action_down);
        acti = new Tutorial();
    Tutorial.PlayPause myPlayPause = acti.new PlayPause();
    myLecture.execute(Tutorial.Buttonlist);
    }
    else
    {
    Tutorial.play=0;
    Tutorial.lecture.cancel(true);
    Tutorial.Play.setBackgroundResource(R.drawable.action);
    }
}

 }

But it doesn't work. when I click on buttons and I touch Play/Pause, I have this :

07-02 11:06:01.350: E/AndroidRuntime(7883): FATAL EXCEPTION: AsyncTask #1
07-02 11:06:01.350: E/AndroidRuntime(7883): Caused by: java.lang.NullPointerException
07-02 11:06:01.350: E/AndroidRuntime(7883):     at com.Tutorial.Tutorial$PlayPause.doInBackground(Tutorial.java:603)
07-02 11:06:01.350: E/AndroidRuntime(7883):     at com.Tutorial.Tutorial$PlayPause.doInBackground(Tutorial.java:1)

And I don't know how to get rid of this error. Obviously, the Asynctask doesn't find the Buttonlist activated status, even if the list is static. I don't know how to access these buttons' states, isPressed doesn't work either.

Thanks for reading and helping me !