Gallery添加OnTouch事件有关问题

dc_detail_gallery.setOnTouchListener(new View.OnTouchListener() {            @Overridepublic boolean onTouch(View v, MotionEvent event) {// TODO Auto-generated method stub  int action = event.getAction();  switch (action) {    case MotionEvent.ACTION_DOWN:      first_x = event.getX();    case MotionEvent.ACTION_MOVE:      last_x = event.getX();    case MotionEvent.ACTION_UP:      last_x = event.getX();    break;  }if (index >= 0 && index <= images.length){  if(last_x < first_x) {    if(index == images.length)       dc_detail_gallery.setAdapter(new DcDetailGalleryAdapter(DcDetail.this, images, texts, prices,index));  else    dc_detail_gallery.setAdapter(new DcDetailGalleryAdapter(DcDetail.this, images, texts, prices,++index));}if(last_x > first_x) {    if(index > 0)       dc_detail_gallery.setAdapter(new  DcDetailGalleryAdapter(DcDetail.this, images, texts, prices,--index));  }}  return true;}});