costume BitmapDrawable getBitMap gibt nichts zurück

import android.content.*;
import android.graphics.*;
import android.graphics.drawable.*;

public class NotificationIconCounter extends BitmapDrawable
{
private int _icon;
private String _text;
private Paint _paint;
private Context _context;
public NotificationIconCounter(Context context, int icon, String text) {
_icon=icon;
_text=text;
_context = context;
_paint = new Paint();
_paint.setTextSize(22f);
_paint.setColor(Color.BLACK);
_paint.setAntiAlias(true);
_paint.setFakeBoldText(true);
_paint.setStyle(Paint.Style.FILL);
_paint.setTextAlign(Paint.Align.CENTER);
}

@Override
public void draw(Canvas p1)
{
// TODO: Implement this method
//Bitmap bm = BitmapFactory.decodeResource(_context.getResources(),  _icon);
//p1.drawBitmap(bm, 0, 0, _paint);
p1.drawText(_text, 0, 0, _paint);
}

@Override
public void setColorFilter(int color, PorterDuff.Mode mode)
{
// TODO: Implement this method
super.setColorFilter(color, mode);
}

@Override
public void setColorFilter(ColorFilter p1)
{
_paint.setColorFilter(p1);
}


@Override
public void setAlpha(int p1)
{
// TODO: Implement this method
_paint.setAlpha(p1);
}

@Override
public int getOpacity()
{
// TODO: Implement this method
return PixelFormat.TRANSLUCENT;
}

}

ImageView test = (ImageView)findViewById(R.id.test);
test.setImageBitmap(new NotificationIconCounter(this, android.R.drawable.ic_dialog_email, "1").getBitmap());