FragmentPagerAdapter不工作

Question

当我创建FragmentPagerAdapter并将页面数定义为3时，页面1将包含内容，页面2将不包含内容，页面3将包含内容。如果我将页数更改为4或更多，则每个页面都有内容。为什么会这样呢？如果我创建了2个页面，没有内容吗？我错过了什么？

下面是我的代码：

public class SectionsPagerAdapter extends FragmentPagerAdapter {

        public SectionsPagerAdapter(FragmentManager fm) {
            super(fm);
        }

    public Fragment getItem(int position) {
        /*
         * Here we are going to return the correct type of fragment for each
         * of the pages
         */
        Log.d("Position", "Default Postion: " + position);
        return MainListFragment.init(position); 

    }

        @Override
        public int getCount() {
            // Show 3 total pages.
            return 3;
        }

我意识到我所有的内容都是一样的，这没什么。这里的重点是，当我有3个页面时，只有2个页面有内容。如果我有4个或更多的页面，一切都会按预期进行。

更奇怪的是，我将输出放到了ListFragment的onCreate方法中，它实际上创建了所有的ListFragments，但并没有全部显示出来。

编辑：

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main_feed);

        RequestUserFeed feed = new RequestUserFeed();
        feed.execute(URL);

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

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

下面是代码的其余部分：

public static class MainListFragment extends ListFragment {
        /**
         * The fragment argument representing the section number for this
         * fragment.
         */

        int fragNum;
        public static final String ARG_SECTION_NUMBER = "section_number";

        private static MainListFragment init(int val) {
            MainListFragment mfl = new MainListFragment();

            Bundle args = new Bundle();
            args.putInt("val", val);
            mfl.setArguments(args);

            return mfl;
        }

        public MainListFragment() {
        }

        /**
         * Retrieving this instance's number from its arguments.
         */
        @Override
        public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            Log.d("Fragment", "Fragment Created for " + getArguments().getInt("val"));
        }

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                Bundle savedInstanceState) {
            View rootView = inflater.inflate(R.layout.setting_fragment,
                    container, false);



            return rootView;
        }

         @Override
            public void onActivityCreated(Bundle savedInstanceState) {
                super.onActivityCreated(savedInstanceState);
                SettingListAdapter settingAdapter = new SettingListAdapter(
                        getActivity().getApplicationContext(),
                        R.layout.setting_item_row, MainFeedActivity.mProfileList);
                ListView listView = (ListView) getActivity().findViewById(android.R.id.list);
                listView.setAdapter(settingAdapter);
            }


    }

在当前状态下，我只能在一个页面上获得列表视图。如果我移动这段代码：

SettingListAdapter settingAdapter = new SettingListAdapter(
                        getActivity().getApplicationContext(),
                        R.layout.setting_item_row, MainFeedActivity.mProfileList);
                ListView listView = (ListView) getActivity().findViewById(android.R.id.list);
                listView.setAdapter(settingAdapter);

对于onCreateView，我将得到一个不同的结果。在onCreateView中设置列表适配器将填充更多页面。令人困惑的是，我知道，但我觉得它值得一提。

Answer 1

为什么在getItem的switch中有这样定义的位置。你有3个项目，所以位置将是0，1，2：

switch (position) {
        case 0:
            Log.d("Position", "Postion: " + position);
            return MainListFragment.init(position); 
        case 1:
            Log.d("Position", "Postion: " + position);
            return MainListFragment.init(position); 
        case 2:
            Log.d("Position", "Postion: " + position);
            return MainListFragment.init(position); 
        }