I have a big project into eclipse.
After I upgraded from SDK manager, R.java gave problems and I deleted it. Now it remains only the folder "gen" empty.
I tried, without success, these things:
-clean project with and without "Build automatically", without any error (reported by eclipse) in the file inside the folder res
-ctrl-shift-o
-remove android.import.R
-F5
space and then remove the add-in manifest
-check the PACKAGE of the project
-restart eclipse
-restart the pc
-exclude the project from eclipse and then import it again
- .. and anything I read in these 2 DAYS
What can I do??
It happened the same thing to me yesterday. I re-open the SDK Manager and suprisely some stuff in the tools folder wer'ent upgraded. Launch the SDK manager and check if you got the last revisions of this stuff. Then restart Eclipse and rebuild your project.
I had the same thing, did you update the SDK the last 2 days? (API 17)? There is probably a problem with that, try updating it again, it will probably work again.
If not you can try Project > Clean. Also the drawable and layouts mustn't contain any errors or capitals...
Might be the same as this.
After updating to SDK Tools to rev. 22 for the first time, you may need to relaunch Android SDK Manager again and install a new item: Android SDK Build-tools.
After installing this, clean your projects and rebuild.
来源：https://stackoverflow.com/questions/16623439/r-java-does-not-regenerate-in-any-way