title: :-1: error: collect2: ld returned 1 exit status. Can anyone please tell why this error?
body: <p>Can anyone please tell why this error? I have included everything ( all header, sources and form class) in my .pro file</p>
  <p>Error message:</p>
  <blockquote>
  <p>debug/moc_calculatorform.o:moc_calculatorform.cpp:(.rdata$_ZTV14CalculatorForm[v‌​table for CalculatorForm]+0xb0):</p>
  <p>undefined reference to `CalculatorForm::changeEvent(QEvent*)'<br />
  collect2: ld returned 1 exit<br />
  status mingw32-make.exe[1]:</p>
  <p>[debug\calculatorform.exe] Error 1
  mingw32-make.exe:<br />
  [debug] Error 2 13:02:27: The process &quot;C:\QtSDK\mingw\bin\mingw32-make.exe&quot; exited with code 2. Error while building project calculatorform (target: Qt Simulator) When executing build step 'Make'</p>
  </blockquote>