java - Android application stopped working -

i making android calculator app class assignment. when press plusminus (+/-) key first , input numeric key; application stops working. when input numeric key , press plusminus button works fine.

else if (v.getid() == r.id.plusminus){         double newnumber = double.parsedouble(textdisplay.gettext().tostring());             total = newnumber * (-1);             textdisplay.settext(total.tostring());          } 

when app crashes, errors in logcat. helpful if post along question , relevant code. however, here pretty sure parsing/error-checking problem

when press plusminus (+/-) key first , input numeric key; application stops working

when press key, aren't checking valid input trying parse empty text. need error-checking such try/catch check invalid input. like

else if (v.getid() == r.id.plusminus){   try {     double newnumber = double.parsedouble(textdisplay.gettext().tostring());         total = newnumber * (-1);         textdisplay.settext(total.tostring());   }   catch (numberformatexception e) {      // maybe show relevant message here toast or       // let user know invalid input entered   }  }