Just adding another thing that worked for me :
react-native link
Evidently my ReactNative files were no longer there. I could figure that out by clicking on
Build Phases -> Link Binary with Libraries ->
Then right clicking a file I knew was responsible for React, and clicking Show In Finder
.
But nothing opened. So assuming the library went missing, I just ran the above command which relinked everything again.
Also if you havn't, try :
rm -rf node_modules/ && npm install