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In my small Android app, I have a ViewPager with 3 pages, each page contains one fragment, that's all working fine with a FragmentStatePagerAdapter (see earlier question).

Now for larger screens, I would like to keep a ViewPager, but I want the first two fragments to be on the same first page.

For this, I implement my own PagerAdapter and this is mostly working, the only problem I am trying to resolve is when I am rotating the screen, I get an error:

12-11 16:34:13.526: ERROR/AndroidRuntime(9221): FATAL EXCEPTION: main
        java.lang.RuntimeException: Unable to start activity ComponentInfo{com.matthieu/com.matthieu.TestActivity}: java.lang.IllegalArgumentException: No view found for id 0x7f030002 (com.matthieu:id/top_fragment) for fragment TestFragment{481a3a98 #0 id=0x7f030002}
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
        at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:3815)
        at android.app.ActivityThread.access$2400(ActivityThread.java:125)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2037)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:123)
        at android.app.ActivityThread.main(ActivityThread.java:4627)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:521)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:871)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:629)
        at dalvik.system.NativeStart.main(Native Method)
        Caused by: java.lang.IllegalArgumentException: No view found for id 0x7f030002 (com.matthieu:id/top_fragment) for fragment TestFragment{481a3a98 #0 id=0x7f030002}
        at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:903)
        at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1088)
        at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1070)
        at android.support.v4.app.FragmentManagerImpl.dispatchActivityCreated(FragmentManager.java:1861)
        at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:547)
        at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1129)
        at android.app.Activity.performStart(Activity.java:3781)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2636)
        ... 12 more

I put a sample code simulating what I am trying to do (and showing this error message) on GitHub.

I guess one problem I have is because of the Fragments I have in the real application, I cannot really have a static newInstance constructor, but instead the Fragments are created ahead of time and have 'setRetainInstance(true);' set.

I understand the id of the viewGroup that will contain the fragment should be part of the hierarchy, and eventually, I guess, it is...

If it makes any difference, I am using the support library and the SherlockActionBar to maintain backwards compatibility with older devices.

Any idea on how to go about this?

EDIT: I have found that if I remove the Fragments from the FragmentManager in onSaveInstanceState I am not getting any crash anymore. All the fragments are recreated from scratch which is not what I want, but I guess I might have to do this and somehow recover those fragments later....

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Matthieu
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    I outlined a few approaches for solving your original problem here: http://commonsware.com/blog/2012/08/20/multiple-view-viewpager-options.html – CommonsWare Dec 17 '12 at 12:15
  • @CommonsWare Mark, thanks for your attention :) I actually read that blog post before. I think only the second approach would work since I am partitioning the page horizontally. I will read again that page and see if I can pick some ideas from there. – Matthieu Dec 17 '12 at 14:38
  • @CommonsWare none of those different approaches work.. the closest one is the 2nd one, but it does not include Fragments in the pages, only simple widgets... I tried everything I could and running out of ideas. Unless somebody really has some good idea, I'll have to go another way about this. – Matthieu Dec 19 '12 at 08:06
  • "the closest one is the 2nd one, but it does not include Fragments in the pages, only simple widgets" -- that blog post was written before nested fragments were added. Nested fragments can be blended into some of these solutions. Here is a reference to a nested fragment version of the second one from my post: https://plus.google.com/u/0/b/114205433913370454414/111289811888358912498/posts/J2VaHs6VodE – CommonsWare Dec 19 '12 at 11:55
  • Are you using getChildFragmentManager() to next the sub-fragments (as you should)? that goes instead of getFragmentManager() or getSupportFragmentManager(); –  Jan 14 '13 at 09:43
  • @YekhezkelYovel, please see the answer I posted... I was not using nested fragments initially.... – Matthieu Jan 14 '13 at 10:40
  • I know you were using nested fragments, I just wanted to state the obvious to make sure your doing it the proper way. Of course I initially assumed the answer will probably be "of course I did". :) –  Jan 14 '13 at 21:57

1 Answers1

18

All right, even though I moved to another way of doing things, I don't like to leave things incomplete...

Going the way of the nested Fragments as suggested by Mark. The link posted in the comments goes to 404, but I found your example code about nested fragments.

A few things I've learned on the way:

  • Nested fragments cannot have setRetainInstance(true), or it will get:

    java.lang.IllegalStateException: Can't retain fragements that are nested in other fragments

  • It was a mistake to create a FrameLayout in the page of the ViewPager to hold the fragment. Looking in the Android code (and specifically the FragmentPagerAdapter), I should just use container.getId() to find where to add the Fragment. Looks like you cannot do anything more sophisticated at that level or it will break.

  • From my understanding, if the fragments hold some information (like I do) that takes a long time to load, the different ways to handle this are:

    • Use onSaveInstanceState (preferred way ?), but not possible if the Fragment is nested. The (empty) constructor will get called when needed by the framework.
    • Use setRetainInstance(true), in that case savedInstanceBundle is always null, but that Fragment (as Java object) will not be destroyed and it will still go through onAttach / onCreateView.
    • Find some other way to save and restore what you need...

Anyway, I pushed my solution using nested fragments on github

Matthieu
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