How to invoke a service on pinch to zoom in android -

i'm wandering possible invoke service on pinch zoom in/out in android, please don't mind if silly doubt you, please me in understanding.

startservice(myservice); 

how invoke service on pinch zoom in on top of activity.

to detect pinch zoom i'm using following code in mainactivity

private static final int invalid_pointer_id = -1;  private int mactivepointerid = invalid_pointer_id;  @override public boolean ontouchevent(motionevent ev) { final int action = ev.getaction(); switch (action & motionevent.action_mask) { case motionevent.action_down: {     final float x = ev.getx();     final float y = ev.gety();      mlasttouchx = x;     mlasttouchy = y;      // save id of pointer     mactivepointerid = ev.getpointerid(0);     break; }  case motionevent.action_move: {     // find index of active pointer , fetch position     final int pointerindex = ev.findpointerindex(mactivepointerid);     final float x = ev.getx(pointerindex);     final float y = ev.gety(pointerindex);      final float dx = x - mlasttouchx;     final float dy = y - mlasttouchy;      mposx += dx;     mposy += dy;      mlasttouchx = x;     mlasttouchy = y;      invalidate();     break; }  case motionevent.action_up: {     mactivepointerid = invalid_pointer_id;     break; }  case motionevent.action_cancel: {     mactivepointerid = invalid_pointer_id;     break; }  case motionevent.action_pointer_up: {     // extract index of pointer left touch sensor     final int pointerindex = (action & motionevent.action_pointer_index_mask)              >> motionevent.action_pointer_index_shift;     final int pointerid = ev.getpointerid(pointerindex);     if (pointerid == mactivepointerid) {         // our active pointer going up. choose new         // active pointer , adjust accordingly.         final int newpointerindex = pointerindex == 0 ? 1 : 0;         mlasttouchx = ev.getx(newpointerindex);         mlasttouchy = ev.gety(newpointerindex);         mactivepointerid = ev.getpointerid(newpointerindex);     }     break; } }  return true; } 

knowledge sharing highly appreciated. in advance.