Question

Current, I have 2 Fragments, which is switch-able through ActionBar‘s tab.

    getSupportActionBar().setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
    ActionBar.Tab newTab = getSupportActionBar().newTab();
    newTab.setText("history");
    newTab.setTabListener(new TabListenerHistoryFragment>(this, "history",
        HistoryFragment.class));

---

 @Override
public void onTabSelected(Tab tab, FragmentTransaction ft) {
    // Check if the fragment is already initialized
    if (mFragment == null) {

        // If not, instantiate and add it to the activity
        mFragment = Fragment.instantiate(mActivity, mClass.getName());
        mFragment.setRetainInstance(true);
        ft.add(android.R.id.content, mFragment, mTag);
    } else {
        // If it exists, simply attach it in order to show it
        ft.attach(mFragment);
    }        
}

I realize the first time of my Activity (This activity is holding 2 fragments) being launched, Fragments’ methods will be called in the following sequence.

onCreate -> onCreateView -> onStart

When I perform Tab switching, and then Tab switching back to the same Fragment, the following methods will be called again.

onCreateView -> onStart

I just wish to retain the same GUI view state, when Tab is being switched back.

• I want my chart continue to be zoomed into previous level.
• I want my chart horizontal scroll stay at previous level.
• I want my list continue scroll stay at previous level.
• …

I know that I can save/restore simple variables using the following method when Tab switching

android fragment- How to save states of views in a fragment when another fragment is pushed on top of it

But, that is not something I want, as my GUI state is pretty difficult to describe within whole bunch of primitive values.

I try the following approach. Of course it won’t work, as I am getting the following runtime error.

public class HistoryFragment extends Fragment {
    View view = null;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        if (this.view != null) {
            return this.view;
        }
        this.view = inflater.inflate(R.layout.history_activity, container, false); 
    }
}

java.lang.IllegalStateException: The specified child already has a parent. You must call removeView() on the child’s parent first.

I realize the following demo example is able to preserve its fragment GUI state (For instance, the position of vertical scroll of list) when there is Tab switching. But I guess, perhaps it is because they are using ListFragment? As I do not find they perform any special handling to preserve GUI state.

• com.example.android.apis.app.FragmentTabs
• com.example.android.apis.app.LoaderCursor.CursorLoaderListFragment

May I know, how I can avoid from recreating same view when perform tab switching？

Answer 1

I had the same problem, and tried to follow the suggestion in the error message.
I tried the following code, and it worked for me.

public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle state)  {
     if (mMyView == null) {
         mMyView = new MyView(getActivity());
     } else {
         ((ViewGroup) mMyView.getParent()).removeView(mMyView);
     }

     return mPuzzleView; 
}