How to add dynamic fragment tab items

Question

I want to add dynamic tab items. I have a fragment which is FragmentOne and it has a TextView. I'm trying create FragmentOne in foreach and add to tabs. I tested code which is in setupViewPager but it doesn't work. How can I edit TextView which in fragments?

if I remove this lines it works but contents of fragment always show default that = "TAB ONE". I want to edit all TextView which is in fragments that created at run time;

View view = fView.getView();

TextView txtTabItemNumber = (TextView)view.findViewById(R.id.txtTabItemNumber);
txtTabItemNumber.setText("TAB " + i);

DynamicTabsActivity.java

public class DynamicTabsActivity extends AppCompatActivity {

    private Toolbar toolbar;
    private TabLayout tabLayout;
    private ViewPager viewPager;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_dynamic_tabs);


        toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);

        viewPager = (ViewPager) findViewById(R.id.viewpager);
        setupViewPager(viewPager);

        tabLayout = (TabLayout) findViewById(R.id.tabs);
        tabLayout.setupWithViewPager(viewPager);
    }


    private void setupViewPager(ViewPager viewPager) {

        ViewPagerAdapter adapter = new ViewPagerAdapter(getSupportFragmentManager());
        LayoutInflater inflator = (LayoutInflater) getSystemService(Context.LAYOUT_INFLATER_SERVICE);

        int count = 10;
        for (int i=0; i<count; i++){

            OneFragment fView = new OneFragment();
            View view = fView.getView();

            TextView txtTabItemNumber = (TextView)view.findViewById(R.id.txtTabItemNumber);
            txtTabItemNumber.setText("TAB " + i);
            adapter.addFrag(fView,"TAB " + i);
        }

        viewPager.setAdapter(adapter);
    }

    class ViewPagerAdapter extends FragmentPagerAdapter {
        private final List<Fragment> mFragmentList = new ArrayList<>();
        private final List<String> mFragmentTitleList = new ArrayList<>();

        public ViewPagerAdapter(FragmentManager manager) {
            super(manager);
        }

        @Override
        public Fragment getItem(int position) {
            return mFragmentList.get(position);
        }

        @Override
        public int getCount() {
            return mFragmentList.size();
        }

        public void addFrag(Fragment fragment, String title) {
            mFragmentList.add(fragment);
            mFragmentTitleList.add(title);
        }

        @Override
        public CharSequence getPageTitle(int position) {
            return mFragmentTitleList.get(position);
        }
    }
}

activity_dynamic_tabs.xml

<android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <android.support.design.widget.AppBarLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar">

        <android.support.v7.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="?attr/colorPrimary"
            app:layout_scrollFlags="scroll|enterAlways"
            app:popupTheme="@style/ThemeOverlay.AppCompat.Light" />

        <android.support.design.widget.TabLayout
            android:id="@+id/tabs"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            app:tabMode="scrollable"/>
    </android.support.design.widget.AppBarLayout>

    <android.support.v4.view.ViewPager
        android:id="@+id/viewpager"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_behavior="@string/appbar_scrolling_view_behavior" />
</android.support.design.widget.CoordinatorLayout>

OneFragment.java

public class OneFragment extends Fragment{

    public OneFragment() {
        // Required empty public constructor
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_one, container, false);

    }

}

fragment_one.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="info.androidhive.materialtabs.fragments.OneFragment">

    <TextView
        android:id="@+id/txtTabItemNumber"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="TAB ONE"
        android:textSize="40dp"
        android:textStyle="bold"
        android:layout_centerInParent="true"/>

</RelativeLayout>

Answer 1

The fragment's layout hasn't been created at point that you call findViewById below:

        OneFragment fView = new OneFragment();
        View view = fView.getView();

        TextView txtTabItemNumber = (TextView)view.findViewById(R.id.txtTabItemNumber);

Following is more typically way this is coded:

public static class OneFragment extends Fragment {
    private static final String ARG_SECTION_NUMBER = "section_number";
    private int sectionNumber;

    public OneFragment() {
    }

    public static OneFragment newInstance(int sectionNumber) {
        OneFragment fragment = new OneFragment();
        Bundle args = new Bundle();
        args.putInt(ARG_SECTION_NUMBER, sectionNumber);
        fragment.setArguments(args);
        return fragment;
    }

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

        sectionNumber = getArguments().getInt(ARG_SECTION_NUMBER);
        TextView textView = (TextView) rootView.findViewById(R.id.txtTabItemNumber);
        textView.setText("TAB " + sectionNumber);
        return rootView;
    }
}

you might also want to move fragment creation in to adapter...for example:

    public Fragment getItem(int position) {
        return OneFragment.newInstance(position + 1);
    }