why is Android MotionEvent.getHistoricalX is thowing an exception -

i using gesturedetector.ongesturelistener in order implement pinch-to-zoom in android. extending textview class , therefore method settextsize() implemented. following code onscroll().

 @override  public boolean onscroll(motionevent e1, motionevent e2, float distancex, float distancey) {      if(logging) log.v(module_name, "onscroll()");       float x, y;      float olddist, newdist;       if (e2.getpointercount() == 2 &&           ((e2.getaction() & motionevent.action_mask) == motionevent.action_move)) {          x = e2.gethistoricalx(0, 0) - e2.gethistoricalx(1, 0);          y = e2.gethistoricaly(0, 0) - e2.gethistoricaly(1, 0);          olddist = floatmath.sqrt(x * x + y * y);          if (olddist > 10) {              if (logging) log.d(module_name, "starting zoom mode");                                  x = e2.getx(0) - e2.getx(1);              y = e2.gety(0) - e2.gety(1);              newdist = floatmath.sqrt(x * x + y * y);               if (newdist > 30) {                     float scalefactor = (newdist > olddist) ? olddist : newdist;                     float scale = (newdist - olddist) / scalefactor;                     // callback processed in main thread                     settextsize(scale * currenttextsize);                     olddist = newdist;              }                    scrolldetected = true;              return true;          }      }      return false;              } 

my problem occasionally, not always, gethistoricalx() throws exception. attaching logcat result.

07-31 16:53:30.358: v/zoomtextview(19540): onscroll() 07-31 16:53:30.358: e/inputeventreceiver(19540): exception dispatching input event. 07-31 16:53:30.358: e/messagequeue-jni(19540): exception in messagequeue callback: handlereceivecallback 07-31 16:53:30.358: e/messagequeue-jni(19540): java.lang.illegalargumentexception: historypos out of range 07-31 16:53:30.358: e/messagequeue-jni(19540):  @ android.view.motionevent.nativegetaxisvalue(native method) 07-31 16:53:30.358: e/messagequeue-jni(19540):  @ android.view.motionevent.gethistoricalx(motionevent.java:2739) 

since know there 2 pointers , history @ least size of 0, not clear me how or why exception occurs. can please assist?

i saw this similar question, , of no me.

before using gethistoricalx() or gethistoricaly(), should check size gethistorysize().

if returns zero, know there no historical events. have process current events, using getx() , gety().