Question

I have a parent SherlockFragmentActivity class that contains ViewPager with 4 Fragments inside.
One of them extends from SherlockListFragment and I want to scroll it to top by click on it’s tab.

MainActivity class:

public class MainActivity extends SherlockFragmentActivity  {

ViewPager viewPager;
TabAdapter tabAdapter;

@Override
public void onCreate(Bundle savedInstanceState) {
    setTheme(Constants.THEME);

    viewPager = new ViewPager(this);
    viewPager.setId(R.id.pager);
    viewPager.setBackgroundResource(R.color.background_color);

    tabAdapter = new TabAdapter(this,viewPager);

    super.onCreate(savedInstanceState);
    setContentView(viewPager);

    // Action bar setup
    setupTabs(savedInstanceState);
}

private void setupTabs(Bundle savedInstanceState) {
    final ActionBar actionBar = getSupportActionBar();
    actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);

    for (int i = 1; i <= 4; i++) {
        ActionBar.Tab tab = getSupportActionBar().newTab();
        switch (i) {
            case 1:
                tab.setText(R.string.feed).setTabListener(tabAdapter);
                tabAdapter.addTab(EventListFragment.class);
                break;
            case 2:
                tab.setText(R.string.downloads).setTabListener(tabAdapter);
                tabAdapter.addTab(LocalEventListFragment.class);
                break;
            case 3:
                tab.setText(R.string.tags).setTabListener(tabAdapter);
                tabAdapter.addTab(TagsFragment.class);
                break;
            case 4:
                tab.setText(R.string.settings).setTabListener(tabAdapter);
                tabAdapter.addTab(SettingsFragment.class);
                break;
        }
        getSupportActionBar().addTab(tab);
    }
}

TabAdapter class:

public static class TabAdapter extends FragmentPagerAdapter implements ViewPager.OnPageChangeListener, ActionBar.TabListener {

    private final Context mContext;
    private final ArrayList<Class<?>> classes = new ArrayList<Class<?>>();
    private final ArrayList<Fragment> mFragments = new ArrayList<Fragment>();
    private final ActionBar mActionBar;
    private final ViewPager mViewPager;

    public TabAdapter(SherlockFragmentActivity activity, ViewPager pager){
        super(activity.getSupportFragmentManager());
        mContext = activity;
        mActionBar = activity.getSupportActionBar();
        mViewPager = pager;
        mViewPager.setAdapter(this);
        mViewPager.setOnPageChangeListener(this);
    }

    public void addTab(Class<?> clss){
        classes.add(clss);
        mFragments.add(Fragment.instantiate(mContext, clss.getName(),
                null));
    }

    @Override
    public Fragment getItem(int i) {
        return mFragments.get(i);
    }

    public int getId(int index){
        return mFragments.get(index).getId();
    }

    @Override
    public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
    }

    @Override
    public void onPageSelected(int position) {
        // fixed double call onTabReselected
        if (mActionBar.getSelectedNavigationIndex() != position)
            mActionBar.setSelectedNavigationItem(position);
    }

    @Override
    public void onPageScrollStateChanged(int i) {
    }

    @Override
    public int getCount() {
        return 4;
    }

    @Override
    public void onTabSelected(ActionBar.Tab tab, FragmentTransaction ft) {
        mViewPager.setCurrentItem(tab.getPosition());
    }

    @Override
    public void onTabUnselected(ActionBar.Tab tab, FragmentTransaction ft) {
    }

    @Override
    public void onTabReselected(ActionBar.Tab tab, FragmentTransaction ft) {
        final int position = tab.getPosition();
        final Fragment fragment =  mFragments.get(position);
        if (fragment != null) {
            switch (position) {
                case 0:
                    // call tab's ListFragment scroll to top item
                    ((EventListFragment) fragment).scrollToTop();
                    break;
                case 1:
                    // do something
                    break;
        }
    }
}

onTabReselected called, then user press current tab, so I try to do EventListFragment scrolling:

EventListFragment class:

public class EventListFragment extends SherlockListFragment {

    @Override
    public void onCreate(Bundle state) {
        super.onCreate(state);
        mAdapter = new EventListAdapter(getSherlockActivity());
        setListAdapter(mAdapter);
    }

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        setRetainInstance(true);
    }

   @Override
   public final View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View eventListLayout = inflater.inflate(R.layout.eventlist_fragment,null);
        ListView lv = (ListView) eventListLayout.findViewById(android.R.id.list);
        ViewGroup parent = (ViewGroup) lv.getParent();
        //Remove ListView and add PullToRefreshListView in its place
        int lvIndex = parent.indexOfChild(lv);
        parent.removeViewAt(lvIndex);
        mPullToRefreshListView = onCreatePullToRefreshListView(inflater, savedInstanceState);
        parent.addView(mPullToRefreshListView, lvIndex, lv.getLayoutParams());
        return eventListLayout;
   }

   public void scrollToTop() {
      if (getSherlockActivity() != null) {  // null after screen rotation
        final ListView listView =  getListView();
        listView.post(new Runnable(){
        public void run() {
            listView.smoothScrollToPosition(0);
        }});
      }
   }

It works on application start, but after screen rotation scrollToTop – getSherlockActivity() returns null.
If remove this condition check, have an exception:

java.lang.IllegalStateException: Content view not yet created
at android.support.v4.app.ListFragment.ensureList(ListFragment.java:328)
at android.support.v4.app.ListFragment.getListView(ListFragment.java:222)
at com.project.fragment.EventListFragment.scrollToTop(EventListFragment.java:337)
at com.project.MainActivity$TabAdapter.onTabReselected(MainActivity.java:411)
at com.actionbarsherlock.internal.app.ActionBarWrapper$TabWrapper.onTabReselected(ActionBarWrapper.java:327)

I haven’t totally understatinding how to ViewPager and its FragmentPagerAdapter works. So can’t find a problem, that occurs.

Answer 1

Applied solution according to this post:

MainActivity class:

//...
@Override
protected void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    FragmentManager manager = getSupportFragmentManager();
    for (int i = 0; i < tabAdapter.getClasses().size(); i++) {
        String className = tabAdapter.getClasses().get(i).getName();
        if (manager.findFragmentByTag(className) != null) {
            manager.putFragment(outState, className, manager.findFragmentByTag(className));
        }
    }
}
//...

TabAdapter class:

//...
public void addTab(Class<?> clss, FragmentManager manager, Bundle savedInstanceState) {
        classes.add(clss);
        String className = clss.getName();
        tags.add(className);
        Fragment fragment;

        if (savedInstanceState != null) {
            fragment = manager.getFragment(savedInstanceState, className);
            if (fragment == null) {
                fragment = createFragment(className);
                manager.beginTransaction().add(fragment, className);
            }
        } else {
            fragment = createFragment(className);
            manager.beginTransaction().add(fragment, className);
        }
        mFragments.add(fragment);
    }
//...

where createFragment is a simple method, that creates needed fragment by passed class name.