R class missing in Android sample code

I create project from existing Android sample code but "gen" folder doesn't have R class.

I tried:

• Check and uncheck "Build 开发者_JAVA百科automatically"

• "Clean" the project

• Find the R.java in folder structure but it is not there.

but R class still doesn't appear and the java files keep reporting "R cannot be resolved to a variable".

Using Android 2.2, Eclipse 3.6, Windows XP

Create a brand-new Android project in Eclipse. Copy the resource files in and then the Java files from the existing project.