Android : R.id cannot resolve components [duplicate]

This question already has an answer here:

• R.java file not generated automatically Eclipse [duplicate] 7 answers

I have an android project in Android studio which was working fine but is acting strangely now.

The error line is in my listAdapter.java file:

String displayName = (TextView) findViewById(R.id.t_name);

I get a cannot resolve symbol 't_name' error.

Even though t_name is defined in one of my layout files, I get "". After typing R.id., I get (auto)suggestions. Only three components show up and they are from a single different layout file. I used to get a list of components from all my layout files.

I have tried cleaning and rebuilding the project with no change.