Avoid recreating same view when perform tab switching

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)); 

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 @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;  } 

Answer 2

I started searching for a simple solution for this many hours ago and finally stumbled across the answer by @roger which saved me lots of hair....

When using the ViewPager in other implementations, I could simply call:

mViewPager.setOffscreenPageLimit(//number of pages to cache); 

So, I was very surprised it took me so many hours to resolve this. The example he gave wasn't entirely clear though, so for the sake of completeness, here is the code I use for the Fragments in my FragmentTabHost

import android.os.Bundle; import android.support.v4.app.Fragment; import android.view.LayoutInflater; import android.view.View; import android.view.ViewGroup;  public class FragmentExample extends Fragment {      private View rootView;      public FragmentExample() {     }      @Override     public View onCreateView(final LayoutInflater inflater, final ViewGroup container, final Bundle savedInstanceState) {          if (rootView == null) {              rootView = inflater.inflate(R.layout.fragment_example_layout, container, false);              // Initialise your layout here          } else {             ((ViewGroup) rootView.getParent()).removeView(rootView);         }          return rootView;     } } 

I searched for the following key phrases which I'm adding here, in the hope that I may save someone else from the frustration I've just experienced!

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FragmentTabHost save Fragment state

FragmentTabHost views recreated

FragmentTabHost cache Fragments

FragmentTabHost onCreateView Fragment destroyed

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