title: What is .idea folder in Android Studio 3.2.12?
body: <p>I meet the problem <em>Cannot resolve symbol AppCompatActivity</em></p>
  
  <p>I solved the problem by deleting  .idea folder and syncing project with gradle files by the acticle <a href="https://stackoverflow.com/questions/30803405/cannot-resolve-symbol-appcompatactivity-support-v7-libraries-arent-recognized">Cannot resolve symbol AppCompatActivity - Support v7 libraries aren&#39;t recognized?</a></p>
  
  <p>Could tell me what .idea folder is ? Why can I delete it and sync ?</p>