I had some problems with R in one of my Android projects, so I tried Eclipse->Project->Clean. I foolishly did it for all of my projects (what’s the harm, right?). Now Eclipse throws a warning for every last reference to R, and refuses to build anything. Build All does not do anything. Help please!
EDIT: I just noticed that this is similar to:
Link
Clean in Eclipse temporarily destroys Android project with error message: missing required source folder: 'gen'
Perhaps for those that fiddling with Build Automatically does not help, the above will help.
I did not get this particular error message, though.
Reopen Eclipse helps me in such issue, or you can try to uncheck and check again Build Automatically.