Eu preciso alterar o plano de fundo da atividade dinamicamente, selecionando uma imagem de outra atividade. e passando a imagem selecionada de volta para a atividade de chamada, mas quando tento obter a imagem, ela é nula. aqui está o meu código.

  public class SelectGoalBackground extends OrmLiteBaseActivity<DatabaseHelper> {// implements{



GridView gridview ;
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.select_goal_background);
   final String from = getIntent().getExtras().getString("from");
    goalsList = new ArrayList<Goal>();

    try {
        goalsList = getTop3Goals();
    } catch (SQLException e1) {
        // TODO Auto-generated catch block
        e1.printStackTrace();
    } catch (java.sql.SQLException e1) {
        // TODO Auto-generated catch block
        e1.printStackTrace();
    }


     gridview = (GridView) findViewById(R.id.gridview);
    gridview.setAdapter(new ImageAdapter(this));

    gridview.setOnItemClickListener(new OnItemClickListener() {
        public void onItemClick(AdapterView<?> parent, View v, int position, long id) {

           ImageView l = (ImageView)gridview.getChildAt(position);
              Drawable path= l.getDrawable();


            Bitmap bitmap = ((BitmapDrawable)path).getBitmap();

            Intent intent = new Intent(SelectGoalBackground.this, AlarmAppActivity.class);

            intent.putExtra("Bitmap", bitmap);
            startActivity(intent);
            SelectGoalBackground.this.finish();
            return;

    });

}


public class ImageAdapter extends BaseAdapter {
    private Context mContext;

    public ImageAdapter(Context c) {
        mContext = c;
    }

    public int getCount() {
        return mThumbIds.length;
    }

    public Object getItem(int position) {
        return null;
    }

    public long getItemId(int position) {
        return 0;
    }

    // create a new ImageView for each item referenced by the Adapter
    public View getView(int position, View convertView, ViewGroup parent) {
        ImageView imageView;
        if (convertView == null) {  // if it's not recycled, initialize some attributes
            imageView = new ImageView(mContext);
            imageView.setLayoutParams(new GridView.LayoutParams(85, 85));
            imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
            imageView.setPadding(8, 8, 8, 8);
        } else {
            imageView = (ImageView) convertView;
        }
       Bitmap bm = BitmapFactory.decodeResource(getResources(), mThumbIds[position]);
        imageView.setImageBitmap(bm);
        return imageView;
    }

    // references to our images
    private Integer[] mThumbIds = {
            R.drawable.sample_0, R.drawable.sample_1

    };
}

e na chamada de atividade eu recebo este bitmap como este

    RelativeLayout rel_lay = (RelativeLayout) findViewById(R.id.main_lay);
    Bitmap bitmap = (Bitmap)this.getIntent().getParcelableExtra("Bitmap");


    if (bitmap != null) {

        Log.v("bitmap", "not null");
        Drawable drawable = new BitmapDrawable(getResources(), bitmap);
        rel_lay.setBackgroundDrawable(drawable);
    }

mas o bitmap é nulo aqui e não está definindo o plano de fundo dessa atividade. qualquer tipo de ajuda é apreciado, plz ajuda