R.java files not generated in Android / r.java missing in android project in Android

Android will not generate the R.java after a clean if any of the XML files have errors in them. Check for any errors and fix them. R.java will then be built.

If that doesn't work, sometimes Eclipse looses track of the file. Click your project and hit F5 to Refresh the project.

if you run a clean on the project it should regenerate all the generated java files, namely R.

...and...

In Eclipse, under the Project menu, is an option build automatically. That would help you build the R.java file everytime modifications are made. The Clean... option is also there under Project.