cannot create a new Fragment in custom FragmentStatePagerAdapter

Question

I'm trying to pre-populate a FragmentStatePagerAdapter with a list of objects but I cannot instantiate a new fragment.

Background:

My PagerAdapter consists of an ArrayList of Msg objects (mMsgConvoList). MsgConvoList is an ArrayList of all messages from a given thread.

The partitioning of mMsgConvoList creates sublists of 3 msgs each (msgSublist).

Each sublist is put through the while loop to be handled by the PagerAdapter in creating new fragments, and adding additional textviews:

How the logic in the while loop works:

If the count == 2, that means there should be a new fragment, otherwise if the count is 1 to 0, locate the currentFragment and add the Msg (this is where the error occurs).

Error:

The error is occurring after the count == 2. The currentFragment is NULL on the 'else' portion of the while loop (count = 1 or 0). It seems like instantiateItem on the MsgFragment is never called. I'm not sure why this doesn't work when using the loop below.

Caused by: java.lang.NullPointerException
        at to.testing.viewpagertest.MsgPagerActivity.onCreate(MsgPagerActivity.java:55)

If I remove the all the code within the 'else' condition from while loop, the fragment is created and the object is added to the text view:

 if (count == 2){
     mAdapter.addMessages(msgSublist.get(count));
     mAdapter.notifyDataSetChanged();
     mViewPager.setCurrentItem(mAdapter.getCount(), true);

This tells me a few things: The above code, outside of the while loop works, so the dataset is working correctly inside the textView and the fragment is being created successfully. It is only when I try to add an additional Msg object to the existing Array, that the currentFragment never seems to get created. Any suggestions would be much appreciated.

MsgPagerActivity:

    if(mMsgConvoList.size() > 0) {
        List msgPartitions = daoMsg.partitionArray(mMsgConvoList, 3);
        mAdapter = new CustomPagerAdapter(getSupportFragmentManager());
        mViewPager.setAdapter(mAdapter);

        for(int i = msgPartitions.size() - 1; i >= 0; i--){
            //extract msg objects from each sublist
            List<Msg> msgSublist = (List<Msg>)msgPartitions.get(i);
            int count = msgSublist.size() -1;

            while(count >= 0){
                if (count == 2){
                    mAdapter.addMessages(msgSublist.get(count));
                    mAdapter.notifyDataSetChanged();
                    mViewPager.setCurrentItem(mAdapter.getCount(), true);
                }else{
                    mViewPager.setCurrentItem(mAdapter.getCount(), true);
                    MsgFragment currentFragment = (MsgFragment)mAdapter.getFragmentAtPosition(
                            mAdapter.getCount() - 1);
                    currentFragment.addMessage(msgSublist.get(count));
                }
                count--;
            }

So you want to display a Fragment for each msgSublist correct? — Hrafn, Feb 23 '15 at 19:32
That's correct. Each msgSublist contains 3 Msg objects. If the count ==2, it's a new Fragment, otherwise the remaining Msgs are added to the existing fragment. If everything within the 'else' condition is commented out, the program works: The first fragment is added and the Msg populates the txtview. — Futureproof, Feb 23 '15 at 19:37
It looks like the instantiation of the new fragment only occurs after onCreate() of MsgPagerActivity completes. While running through the loop, it never has the chance to finish onCreate() so the first fragment is never created and currentFragment will remain null. I thought notifyDataSetChanged triggered the fragment creation. — Futureproof, Feb 27 '15 at 03:08

cannot create a new Fragment in custom FragmentStatePagerAdapter

0 Answers0