Can't access resources in another thread on Android (crash)

This has been driving me insane for days, i am new to android and i can't seem to figure out how to access resources from other threads. I am trying to schedule a task to execute after a while, here is the relevant code:

public class TikTakBoom extends Activity {

private SensorManager mSensorManager;

public ToggleButton startButton;

private Bitmap mBombOn;
private Bitmap mBombOff;

/** Tik tak boom **/
protected MediaPlayer mediaPlayer;      // play tik tak or boom
protected Timer boomTimer;              // timer 开发者_如何学JAVAfor explosion

// bomb button backgrounds
protected android.graphics.drawable.BitmapDrawable buttonBombOn;
protected android.graphics.drawable.BitmapDrawable buttonBombOff;

// random boom delay in ms
protected long boomDelay = 1500;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    requestWindowFeature(Window.FEATURE_NO_TITLE);

    // tell system to use the layout defined in our XML file
    setContentView(R.layout.main);

    Log.w(this.getClass().getName(), "SIS is null");

    // configure toggle button (bomb on/off)
    startButton = (ToggleButton)findViewById(R.id.toggleButton1);
    startButton.setText("");
    startButton.setTextOn("");
    startButton.setTextOff("");

    // scale bomb images to button size
    mBombOff = BitmapFactory.decodeResource(this.getResources(), R.drawable.bomb_off);
    mBombOff = Bitmap.createScaledBitmap(mBombOff, 120, 120, true);

    mBombOn = BitmapFactory.decodeResource(this.getResources(), R.drawable.bomb_on);
    mBombOn = Bitmap.createScaledBitmap(mBombOn, 120, 120, true);

    buttonBombOn = new android.graphics.drawable.BitmapDrawable(mBombOn);
    buttonBombOff = new android.graphics.drawable.BitmapDrawable(mBombOff);

    startButton.setChecked(false);

    boomTimer = new Timer();

    // onclick listener for toggle bomb on/off
    startButton.setOnClickListener(new OnClickListener() {
        public void onClick(View v) {
            // Perform action on clicks
            if (startButton.isChecked()) {
                mediaPlayer = MediaPlayer.create(getApplicationContext(), R.raw.tik_tak);

                mediaPlayer.setLooping(true);
                mediaPlayer.start();

                // align boom delay with tik tak duration
                boomDelay -= boomDelay%mediaPlayer.getDuration();

                boomTimer.schedule(new BoomTimeTask(getApplicationContext()), boomDelay);

                startButton.setBackgroundDrawable(buttonBombOn);
            } else {
                if (mediaPlayer != null) {
                    mediaPlayer.release();
                    mediaPlayer = null;
                }

                startButton.setBackgroundDrawable(buttonBombOff);
            }
        }

    });
} 

class BoomTimeTask extends TimerTask {
    Context context;

    public BoomTimeTask(Context context) {
        super();

        this.context = context;
    }

    public void run() {
        if (mediaPlayer != null) {
            mediaPlayer.release();
            mediaPlayer = null;
        }

        mediaPlayer = MediaPlayer.create(getApplicationContext(), R.raw.sheldon);

        mediaPlayer.setLooping(false);
        mediaPlayer.start();

        startButton = (ToggleButton)((Activity)context).findViewById(R.id.toggleButton1);

        startButton.setChecked(false);
        //startButton.setBackgroundDrawable(buttonBombOff);
    }
}

App crashes on startButton.setChecked(false) in BoomTimeTask.run(), i am guessing NullPointerException.

Pls help, i am gonna go insane, i have tried everything! Nothing works.. Tried it without the context passed as a parameter, since the reference should be visible to BoomTimeTask thread as well, tried a dozen of other things, just can't get it to work.

What am i missing? Thx in advance, would really appreciate any kind of help. Cheers, Val.

SOLVED: how to change button text dynamically for every 3 sec in android?

You should use

runOnUiThread(new Runnable() { 
    public void run() { 
    // YOUR ACTIONS ON Graphic interface
    } 
}); 

It's because in android you can't modify GUI elements without being in the thread that deal with GUI.

http://developer.android.com/reference/android/app/Activity.html