why android:id isn't added to the R.java in menu resource file?

Question

Now, I am studying the android developer training. In 'Adding Action Buttons' I got some problems. I wrote the xml code like below, but in MainActivity.java, action_search and action_settings got error and compiler said it cannot be resolved or not a field. And then, I read the recommendation to fix the code that "create field action_search in type id". I've already wrote the code "@+id/action_search" and "@+id/action_settings". Why this error appeared please let me know!

<menu xmlns:android="http://schemas.android.com/apk/res/android" >
    <!-- Search, should appear as action button -->
   <item android:id="@+id/action_search"
          android:icon="@drawable/ic_action_search"
          android:title="@string/action_search"
          android:showAsAction="ifRoom" />
    <!-- Settings, should always be in the overflow -->
    <item android:id="@+id/action_settings"
          android:title="@string/action_settings"
          android:showAsAction="never" />
</menu>

EDIT: Code as requested

   public boolean onOptionsItemSelected(MenuItem item) {
        // Handle presses on the action bar items
        switch (item.getItemId()) {
        case R.id.action_search:
                openSearch();
                return true;
        case R.id.action_settings:
                openSettings();
                return true;
        default:
            return super.onOptionsItemSelected(item); 
        } 
    }