Question

This code should be drawing things, but it doesn’t draw anything when I move my finger. Please help me debug it.

  @Override

  protected void onDraw(Canvas canvas) {
    canvas.drawPath(path, paint);
  }
  @Override
  public boolean onTouchEvent(MotionEvent event) {
    float eventX = event.getX();
    float eventY = event.getY();

    switch (event.getAction()) {
      case MotionEvent.ACTION_DOWN:
        path.moveTo(eventX, eventY);
        return true;
      case MotionEvent.ACTION_MOVE:
        path.lineTo(eventX, eventY);
        break;
      case MotionEvent.ACTION_UP:
        // nothing to do 
        break;
      default:
        return false;
    }

    // Schedules a repaint.
    invalidate();
    return true;
  }
} 

Answer 1

Try this

@Override

  protected void onDraw(Canvas canvas)
  {
    canvas.drawPath(path, paint);
  }
  @Override
  public boolean onTouchEvent(MotionEvent event) {
    float eventX = event.getX();
    float eventY = event.getY();

    switch (event.getAction()) {
      case MotionEvent.ACTION_DOWN:
        path.moveTo(eventX, eventY);
        path.lineTo(eventX, eventY);
        return true;
      case MotionEvent.ACTION_MOVE:
        path.quadTo(eventX, eventY, (x + eventX)/2, (y + eventY)/2);
        break;
      case MotionEvent.ACTION_UP:
        canvas.drawPath(path, paint);
        // kill this so we don't double draw
     path.reset();
        break;
      default:
        return false;
    }

    // Schedules a repaint.
    invalidate();
    return true;
  }
} 

For more information take a look

http://code.google.com/p/strokesformartians/source/browse/trunk/src/se/combitech/strokesformartians/drawing/FingerPaint.java?r=120

This may help you.