title: Cannot resolve symbol 'androidx.constraintlayout.widget.ConstraintLayout'
body: <p><a href="https://i.stack.imgur.com/vF1Gu.png" rel="nofollow noreferrer">Cannot resolve symbol 'androidx.constraintlayout.widget.ConstraintLayout'</a></p>
  
  <p>I made an empty activity in Android Studio, ahead of nothing added, in activity_main.xml, there were so many red lines,and the prompt was: Cannot resolve symbol'</p>
  
  <p>while, these code was generated by Android Studio, I tried file->invalidate cashes/restart... and installed all the SDK tools but Google series. The error was still there.</p>
  
  <p>Gradle was successful, and JDK was installed.</p>
  
  <p>Has anyone a solution ?</p>