Android R file not generating

It could be if you have deleted

  <string name="action_settings">Settings</string>

in the strings.xml, but not deleted main.xml file in the menu folder.

have you tried checking for the target API maybe the api is low try doing right click your project >> properties >> andriod >> check the correct API or check if there are any error and fix them first these steps made my r file generate hope it makes yours

I have just had this experience. In my AndroidManifest.xml there was a reference to a theme which didn't exist.

For instance.

<application
    android:allowBackup="true"
    android:icon="@drawable/ic_launcher"
    android:label="@string/app_name"
    android:theme="@style/AppTheme_Lorem" >

There wasn't AppTheme_Lorem among the application's themes