This is a test post to help me figure out why I have received this post in my email, but the topic doesn't seem to have appeared in the Google Groups page. Apologies if this reply shows up for people - I will delete it if I see it appear.
On Fri, Sep 21, 2012 at 10:11 AM, UgglyNoodle <[email protected]>wrote: > I believe that FragmentStatePagerAdapter does not behave correctly when > overriding getItemPosition(Object object) with the purpose of reordering > the pages. > > Below is a simple example. In the initial state, the order of the pages is > {A, B, C}. Upon calling toggleState(), the order of the pages changes to > {A, C, B}. By overriding getItemPosition(Object object), we ensure that the > current page being viewed (A, B, or C) does not change. > > public static class TestPagerAdapter extends FragmentStatePagerAdapter { > private boolean mState = true; > public TestPagerAdapter(FragmentManager fragmentManager) { > super(fragmentManager); > } > @Override > public int getCount() { > return 3; > } > private void toggleState() { > mState = !mState; > notifyDataSetChanged(); > } > private String getLabel(int position) { > switch (position) { > case 0: > return "A"; > case 1: > return mState ? "B" : "C"; > default: > return mState ? "C" : "B"; > } > } > @Override > public int getItemPosition(Object object) { > String label = ((TestFragment) object).getLabel(); > if (label.equals("A")) { > return 0; > } else if (label.equals("B")) { > return mState ? 1 : 2; > } else { > return mState ? 2 : 1; > } > } > @Override > public CharSequence getPageTitle(int position) { > return getLabel(position); > } > @Override > public Fragment getItem(int position) { > return TestFragment.newInstance(getLabel(position)); > } > } > > > I have encountered two separate behaviours which seem incorrect. > > 1. If I immediately call toggleState() (while viewing page A, before > swiping to any other page), the app crashes. > > java.lang.IndexOutOfBoundsException: Invalid index 2, size is 2 > at > java.util.ArrayList.throwIndexOutOfBoundsException(ArrayList.java:251) > at java.util.ArrayList.set(ArrayList.java:477) > at > > android.support.v4.app.FragmentStatePagerAdapter.destroyItem(FragmentStatePagerAdapter.java:136) > at android.support.v4.view.ViewPager.populate(ViewPager.java:867) > at > > android.support.v4.view.ViewPager.setCurrentItemInternal(ViewPager.java:469) > at > > android.support.v4.view.ViewPager.setCurrentItemInternal(ViewPager.java:441) > at > android.support.v4.view.ViewPager.dataSetChanged(ViewPager.java:766) > at > > android.support.v4.view.ViewPager$PagerObserver.onChanged(ViewPager.java:2519) > at > android.database.DataSetObservable.notifyChanged(DataSetObservable.java:37) > at > > android.support.v4.view.PagerAdapter.notifyDataSetChanged(PagerAdapter.java:276) > at > > com.ugglynoodle.test.testfragmentstatepageradapter.MainActivity$TestPagerAdapter.toggleState(MainActivity.java:55) > ... > > Looking at the source (FragmentStatePagerAdapter.java), this would be > fixed by first checking the size of mFragments (as in lines 113-115) before > calling set() in line 136. > > 2. If I first swipe to page B, then getItem(2) is called, page C is > created, and mFragments now has a size of 3 (this will prevent the crash > above from happening in a moment). Then I swipe back to page A, and page C > is destroyed, as it should be (since it is 2 pages away, and I'm using the > default offscreen page limit of 1). Now, I call toggleState(). Page B is > now destroyed. However, page C is NOT recreated! This means, when I now > swipe to the right, I get an empty page. > > First, it would be nice to know whether I'm correct and these are in fact > bugs, or whether I'm doing something wrong. If they are bugs, can anyone > suggest a workaround (other than debugging and rebuilding the support > library myself)? Surely somebody must have overridden > getItemPosition(Object object) successfully (apart from setting everything > to POSITION_NONE)? > > I am using the current revision (10) of the support library. > > -- > You received this message because you are subscribed to the Google > Groups "Android Developers" group. > To post to this group, send email to [email protected] > To unsubscribe from this group, send email to > [email protected] > For more options, visit this group at > http://groups.google.com/group/android-developers?hl=en -- You received this message because you are subscribed to the Google Groups "Android Developers" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/android-developers?hl=en
