问无法访问fragment_main中的id标记

EN

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    // Create the adapter that will return a fragment for each of the three
    // primary sections of the activity.
    mSectionsPagerAdapter = new SectionsPagerAdapter(getFragmentManager());

     savedSearches = getSharedPreferences(SEARCHES, MODE_PRIVATE); 

      // store the saved tags in an ArrayList then sort them
      tags = new ArrayList<String>(savedSearches.getAll().keySet());
      Collections.sort(tags, String.CASE_INSENSITIVE_ORDER); 

      // create ArrayAdapter and use it to bind tags to the ListView
      adapter = new ArrayAdapter<String>(this, R.layout.list_item, tags);

      System.out.println(R.id.list);
      ListView lv = (ListView) findViewById(R.id.list);
      lv.setAdapter(adapter);

    // Set up the ViewPager with the sections adapter.
    mViewPager = (ViewPager) findViewById(R.id.pager);
    mViewPager.setAdapter(mSectionsPagerAdapter);

}