Update ViewPager dynamically?

Question

I can't update the content in ViewPager.

A question: What is the relationship and correct usage of methods instantiateItem() and getItem() in FragmentPagerAdapter class?

I was using only getItem() to instantiate and return my fragments:

@Override
public Fragment getItem(int position) {
    return new MyFragment(context, paramters);
}

This worked well (but as said I can't change the content).

So I found this: ViewPager PagerAdapter not updating the View

Particulary one in which it's talked about method instantiateItem():

"My approach is to use the setTag() method for any instantiated view in the instantiateItem() method"

So now I want to implement instantiateItem() in order to do that. But I don't know what I have to return there (return is Object) and what is the relation with getItem(int position)?

Currently I'm using getItem to instantiate the Fragment, is that wrong? But then do I have to put the fragments in instance variable, or not implement getItem() at all...? I just don't understand it.

I tried reading the reference:

• public abstract Fragment getItem (int position)

  Return the Fragment associated with a specified position.

• public Object instantiateItem (ViewGroup container, int position)

  Create the page for the given position. The adapter is responsible for adding the view to the container given here, although it only must ensure this is done by the time it returns from finishUpdate(ViewGroup). Parameters

  container The containing View in which the page will be shown. position The page position to be instantiated.

  Returns

  Returns an Object representing the new page. This does not need to be a View, but can be some other container of the page.

... but I still don't understand how are they related and what I have to do.

Here's my code. I'm using support package v4.

ViewPagerTest

public class ViewPagerTest extends FragmentActivity {
    private ViewPager pager;
    private MyFragmentAdapter adapter; 

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.pager1);

        pager = (ViewPager)findViewById(R.id.slider);

        String[] data = {"page1", "page2", "page3", "page4", "page5", "page6"};

        adapter = new MyFragmentAdapter(getSupportFragmentManager(), 6, this, data);
        pager.setAdapter(adapter);

        ((Button)findViewById(R.id.button)).setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                reload();
            }
        });
    }

    private void reload() {
        String[] data = {"changed1", "changed2", "changed3", "changed4", "changed5", "changed6"};
        //adapter = new MyFragmentAdapter(getSupportFragmentManager(), 6, this, data);
        adapter.setData(data);
        adapter.notifyDataSetChanged();
        pager.invalidate();

        //pager.setCurrentItem(0);
    }
}

MyFragmentAdapter

class MyFragmentAdapter extends FragmentPagerAdapter {
    private int slideCount;
    private Context context;
    private String[] data;

    public MyFragmentAdapter(FragmentManager fm, int slideCount, Context context, String[] data) {
        super(fm);
        this.slideCount = slideCount;
        this.context = context;
        this.data = data;
    }

    @Override
    public Fragment getItem(int position) {
        return new MyFragment(data[position], context);
    }

    @Override
    public int getCount() {
        return slideCount;
    }

    public void setData(String[] data) {
        this.data = data;
    }

    @Override
    public int getItemPosition(Object object) {
        return POSITION_NONE;
    }
}

MyFragment

public final class MyFragment extends Fragment {
    private String text;

    public MyFragment(String text, Context context) {
        this.text = text;
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.slide, null);
        ((TextView)view.findViewById(R.id.text)).setText(text);

        return view;
    }
}

Here is also somebody with a similar problem, no answers...

http://www.mail-archive.com/[e-mail]/msg200477.html

Answer 1

Use FragmentStatePagerAdapter instead of FragmentPagerAdapter if you want to recreate or reload fragment on index basis For example if you want to reload fragment other than FirstFragment, you can check instance and return position like this

 public int getItemPosition(Object item) {
    if(item instanceof FirstFragment){
       return 0;
    }
    return POSITION_NONE;
 }

Answer 2

I have lived same problem and I have searched too much times. Any answer given in stackoverflow or via google was not solution for my problem. My problem was easy. I have a list, I show this list with viewpager. When I add a new element to head of the list and I refresh the viewpager nothings changed. My final solution was very easy anybody can use. When a new element added to list and want to refresh the list. Firstly set viewpager adapter to null then recreate the adapter and set i to it to viewpager.

myVPager.setAdapter(null);
myFragmentAdapter = new MyFragmentAdapter(getSupportFragmentManager(),newList);
myVPager.setAdapter(myFragmentAdapter);

Be sure your adapter must extend FragmentStatePagerAdapter

Answer 3

I slightly modified the solution provided by Bill Phillips to suit my needs

private class PagerAdapter extends FragmentStatePagerAdapter{
    Bundle oBundle;
    FragmentManager oFragmentManager;
    ArrayList<Fragment> oPooledFragments;

public PagerAdapter(FragmentManager fm) {
    super(fm);
    oFragmentManager=fm;

    }
@Override
public int getItemPosition(Object object) {

    Fragment oFragment=(Fragment)object;
    oPooledFragments=new ArrayList<>(oFragmentManager.getFragments());
    if(oPooledFragments.contains(oFragment))
        return POSITION_NONE;
    else
        return POSITION_UNCHANGED;
    } 
}

so that the getItemPosition() returns POSITION_NONE only for those fragments which are currently in the FragmentManager when getItemPosition is called. (Note that this FragmentStatePager and the ViewPager associated with it are contained in a Fragment not in a Activity)

Answer 4

I know am late for the Party. I've fixed the problem by calling TabLayout#setupWithViewPager(myViewPager); just after FragmentPagerAdapter#notifyDataSetChanged();

Answer 5

for those who still face the same problem which i faced before when i have a ViewPager with 7 fragments. the default for these fragments to load the english content from api service but the problem here that i want to change the language from settings activity and after finish settings activity i want ViewPager in main activity to refresh the fragments to match the language selection from the user and load the Arabic content if user choosed Arabic here what i did to work from the first time

1- You must use FragmentStatePagerAdapter as mentioned above.

2-on mainActivity i override the onResume and did the following

 if (!(mPagerAdapter == null)) {
mPagerAdapter.notifyDataSetChanged();
}

3-i overrided the getItemPosition() in mPagerAdapter and make it return POSITION_NONE.

 @Override
   public int getItemPosition(Object object) {
     return POSITION_NONE;
    }

works like charm

Answer 6

I use EventBus library to update Fragment content in ViewPager. The logic is simple, just like document of EventBus how to do. It is no need to control FragmentPagerAdapter instance. The code is here:

1: Define events

Define which message which is needed to update.

public class UpdateCountEvent {
    public final int count;

    public UpdateCountEvent(int count) {
        this.count = count;
    }
}

2.Prepare subscribers

Write below code in the Fragment which is needed update.

@Override
public void onStart() {
    super.onStart();
    EventBus.getDefault().register(this);
}

@Override
public void onStop() {
    EventBus.getDefault().unregister(this);  
    super.onStop();
}

public void onEvent(UpdateCountEvent event) {//get update message
    Toast.makeText(getActivity(), event.count, Toast.LENGTH_SHORT).show();
}

3.Post events

Write below code in other Activity or other Fragment which needs to update parameter

//input update message
EventBus.getDefault().post(new UpdateCountEvent(count));