Android: Best Approach to pass data between viewpager fragments

Question

I have 3 fragments in a ViewPager Activity. All 3 fragments have input fields. Here I am trying to pass first two fragments data to third fragment. I read few posts here and

Answer 1

Okay, I Had same issue to pass data(not just string) between two tabs in a ViewPager. So here is what i did. I Use interfaces to communicate between the different components.

The data passes this way:

Tab 1 -> Activity -> VewPageAdapter -> Tab 2

1. In Tab 1

create an interface.

OnCartsDataListener mOncarOnCartsDataListener;


public interface OnCartsDataListener {

    public void onCartsDataReceived(ArrayList<CartsViewModel> cartsViewModels);

}

@Override
public void onAttach(Activity activity) {
    super.onAttach(activity);
    try {
        mOncarOnCartsDataListener = (OnCartsDataListener)activity;
    }catch (ClassCastException e){

    }

}
// now call mOncarOnCartsDataListener.onCartsDataReceived(data) when you have the data

2. In Activity

Implement the interface and override the method

ViewPagerAdapter adapter;
adapter = new ViewPagerAdapter(getSupportFragmentManager(), Titles, Numboftabs);

@Override
public void onCartsDataReceived(ArrayList<CartsViewModel> cartsViewModels) {
    Log.d(TAG, "data received to Activity... send to view pager");
    adapter.onCartsDataReceived(cartsViewModels);
}

3.IN ViewPagerAdapter

Also implements the interface and override the method

@Override
public void onCartsDataReceived(ArrayList<CartsViewModel> cartsViewModels) {
    Log.d(TAG, "data received to view pager... sending to tab 2");

    if(tab2!=null){
        tab2.onCartsDataReceived(cartsViewModels);
    }else{
        Log.d(TAG, "tab2 is null");
    }
} 

4. Finally tab 2

Also implements the interface and override the method

@Override
public void onCartsDataReceived(ArrayList<CartsViewModel> cartsViewModels) {
    Log.d(TAG, "Finally ! received data to tab 2");
    if(cartsViewModels!=null){
        for(CartsViewModel cart : cartsViewModels){
            Log.d(TAG,"got it :"+cart.getCartName());
        }
    }
}

Answer 2

Since AndroidX, you can create a ViewModel and share data between Activity and all fragments within ViewPager

Read here how to

Answer 3

Can you do something like this? First create any data structure like Arraylist in your main activity. Then send a reference of that data model to your fragments. Now update that data when, on change your text fields. By doing this all the fragment can see updated values. So fragments can update this data itself and we don't need to send that data since it is already shared. I'll explain this using your example. Try to improve this. You can maintain fragment specific data model then each fragment can access data with the knowledge of that data owner.

TabsPagerAdapter.java

public class TabsPagerAdapter extends FragmentPagerAdapter {

    public TabsPagerAdapter(FragmentManager fm,SubmitPostActivity activity){
        super(fm);
    }


    @Override
       public Fragment getItem(int index) {

       switch(index) {

          case 0 : //PostInfoFragment
                     return new PostInfoFragment(0,activity);

          case 1 : //LocationInfoFragment
                    return new LocationInfoFragment(1,activity);

          case 2 : //PersonalInfoFragment
                     return new PersonalInfoFragment(2,activity);

        }
        return null;
    }

    @Override
    public int getCount() {       
       return 3;
    }

}

ViewPagerActivity -- >

package com.jbandroid;

public class SubmitPostActivity extends FragmentActivity implements ActionBar.TabListener,LocationInfoFragment.setLocationInfo{

    private ViewPager viewpager;
    private ActionBar actionBar;
    private TabsPagerAdapter mAdapter;
     FragmentManager manager;
     PersonalInfoFragment frag;
     List<String> location;
    /*private MenuItem myActionMenuItem;
      private Button myActionButton;*/


    //Tab titles
    private String[] tabs  = {"Post Info" , "Location Info" , "Personal Info" };
    public List<String> dataModel = new ArrayList<String>();


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.action_submit_post);

        viewpager = (ViewPager) findViewById(R.id.pager);
        actionBar = getActionBar();
        manager = getSupportFragmentManager();
        mAdapter = new TabsPagerAdapter(getSupportFragmentManager(),this);
        //viewpager.setOffscreenPageLimit(2);
        viewpager.setAdapter(mAdapter);

        //actionBar.setHomeButtonEnabled(false);
        actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);

        for (String tab : tabs){
            actionBar.addTab(actionBar.newTab().setText(tab).setTabListener(this));
        }

        if(savedInstanceState != null){
            actionBar.setSelectedNavigationItem( savedInstanceState.getInt("tab",0));
        }

    }

}

1st Fragment =>

public class PostInfoFragment extends Fragment {

    private MenuItem myActionMenuItem;
    private Button myActionButton;
    private ActionBar actionBar;
    private String post_title, post_desc,post_status;

    private EditText submit_post_title, submit_post_desc;
    private int position;
    private Resources res;

    SubmitPostActivity callingActivity;
    List<String> post_details;

    public PostInfoFragment(int position,SubmitPostActivity callingActivity )
    {
        this.callingActivity = callingActivity;
        this.position = position;
    }

    //RelativeLayout rel_submit_post_start_date,rel_submit_post_end_date;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.fragment_post_info,
                container, false);

        /*if(!imageLoader.isInited()){*/
        initImageLoader();
        /*}*/

        //handler = new Handler();


        submit_post_title = (EditText) rootView
                .findViewById(R.id.submit_post_title);
        submit_post_desc = (EditText) rootView
                .findViewById(R.id.submit_post_description);

        actionBar = getActivity().getActionBar();
        setHasOptionsMenu(true);

        post_details = new ArrayList<String>();
        res = getResources();

        setListeners();

        Log.d("postinfo_oncreate view", "postinfo_oncreate view");

        //this is editText onchange listner do the same for submit_post_desc as well
        submit_post_title.addTextChangedListener( new TextWatcher()
        {

            @Override
            public void onTextChanged( CharSequence s, int start, int before, int count )
            {

            }

            @Override
            public void beforeTextChanged( CharSequence s, int start, int count, int after )
            {
            }

            @Override
            public void afterTextChanged( Editable s )
            {
                if( callingActivity != null )
                {
                //use this.position in order to update relevant data 
                    List<String> post_details = callingActivity.dataModel;
                    if( post_details == null )
                    {
                        post_details = new ArrayList<String>();
                    }
                    post_details.add(s.toString());
                }
            }
        } );


        return rootView;

    }

    //making sure if the parent activity has implemented interface
    @Override
    public void onAttach(Activity activity) {
        super.onAttach(activity);
        // This makes sure that the container activity has implemented
        // the callback interface. If not, it throws an exception
        try {
            callingActivity = (SubmitPostActivity) activity;
        } catch (ClassCastException e) {

            throw new ClassCastException(activity.toString()
                    + "must implemet setPostInfo");
        }

         Log.d("postinfo_onattach", "postinfo_onattach");
    }
}

Please not that this may not compile as it is. Try to get the concept.