Как динамически обновить ViewPager при удалении фрагмента

Question

Мне жаль вопрос, на который уже дан ответ в этой сети, но я не могу найти тот же случай с моим.

Я вызываю списки из нескольких столбцов с RoomDatabase для SetText в ViewPager, и мой вопрос заключается в том, как динамически обновлять ViewPager при удалении записи. В других вопросах, которые я проверял, был TextView в ViewPager. Но в моем случае я присваиваю массивы, полученные через пакет, каждому TextView в ArrayListFragment классе.

Это так расстраивает после поиска того, что делать после 'myAdapter.notifyDataSetChanged ()' в кнопка удаления.

Буду очень признателен за вашу помощь.

public class FragmentStateLibraryPagerSupport extends Fragment {

    MyAdapter myAdapter;
    ViewPager mPager;
    public List<String> head_array;
    public List<String> desc_array;
    TodoDatabase db;

    @Nullable
    @Override
    public View onCreateView(@NonNull final LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        final View root = inflater.inflate( R.layout.fragment_pager, null );
        Button btn_delete = root.findViewById( R.id.btn_delete );
        btn_delete.setOnClickListener( new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                ArrayListFragment arrayListFragment = new ArrayListFragment();
                String head_array_text = head_array.get( arrayListFragment.return_mNum() );
                Log.e( "head_array_text ::" ,  head_array.get( arrayListFragment.return_mNum() ));

                TodoDatabase db = Room.databaseBuilder( getContext(), TodoDatabase.class, "todo-db" ).allowMainThreadQueries().build();
                db.todoDao().deleteRecord( head_array_text );
                myAdapter.notifyDataSetChanged();
            }
        } );
        return root;
    }
    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated( view, savedInstanceState );
        db = Room.databaseBuilder( getContext(), TodoDatabase.class, "todo-db" ).allowMainThreadQueries().build();

        head_array = db.todoDao().getAllHead();
        desc_array = db.todoDao().getAllDesc();

        myAdapter = new MyAdapter( getChildFragmentManager() );

        mPager = (ViewPager) view.findViewById( R.id.pager );
        mPager.setAdapter( myAdapter );
    }
    private class MyAdapter extends FragmentStatePagerAdapter {

        public MyAdapter(FragmentManager fm) {
            super( fm, BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT );
        }

        @NonNull
        @Override
        public Fragment getItem(int position) {
            return ArrayListFragment.newInstance( position, head_array, desc_array );
        }

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

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

    public static class ArrayListFragment extends ListFragment {
        int mNum;
        ArrayList<String> head_array, desc_array;
        Button btn_save;

        public int return_mNum(){
            return mNum;
        }

        static ArrayListFragment newInstance(int num, List<String> head_array, List<String> desc_array) {
            ArrayListFragment arrayListFragment = new ArrayListFragment();
            Bundle bundle = new Bundle();
            bundle.putInt( "num", num );
            bundle.putStringArrayList( "head_array", (ArrayList<String>) head_array );
            bundle.putStringArrayList( "desc_array", (ArrayList<String>) desc_array );
            arrayListFragment.setArguments( bundle );
            return arrayListFragment;
        }

        @Override
        public void onCreate(@Nullable Bundle savedInstanceState) {
            super.onCreate( savedInstanceState );
            mNum = getArguments() != null ? getArguments().getInt( "num" ) : 1;
            head_array = getArguments().getStringArrayList( "head_array" );
            desc_array = getArguments().getStringArrayList( "desc_array" );
        }

        @Nullable
        @Override
        public View onCreateView(@NonNull final LayoutInflater inflater, @Nullable final ViewGroup container, @Nullable Bundle savedInstanceState) {
            View v = inflater.inflate( R.layout.fragment_pager_list, container, false );
            btn_save = v.findViewById( R.id.btn_save );

            final View head_tv = v.findViewById( R.id.head_tv );
            final View desc_tv = v.findViewById( R.id.desc_tv );

            if (head_array.size() == 0) {
                ((TextView) head_tv).setText( R.string.when_no_data_in_DB );
                ((TextView) desc_tv ).setText( "" );

                btn_save.setVisibility( View.INVISIBLE );
            } else {
                ((TextView) head_tv).setText( head_array.get( mNum ) );
                ((TextView) desc_tv ).setText( getString( Integer.parseInt( desc_array.get( mNum ) ) ) );
            }
            return v;
        }
    }
}

Answer 1

FragmentPagerAdapter на самом деле не предназначен для поддержки возможности удаления элементов (динамический c количество элементов фрагмента).

Для этого вам следует использовать следующий код, который отслеживает идентификаторы, а не фрагменты по позиции.

public class DynamicFragmentPagerAdapter extends PagerAdapter {
private static final String TAG = "DynamicFragmentPagerAdapter";

private final FragmentManager fragmentManager;

public static abstract class FragmentIdentifier implements Parcelable {
    private final String fragmentTag;
    private final Bundle args;

    public FragmentIdentifier(@NonNull String fragmentTag, @Nullable Bundle args) {
        this.fragmentTag = fragmentTag;
        this.args = args;
    }

    protected FragmentIdentifier(Parcel in) {
        fragmentTag = in.readString();
        args = in.readBundle(getClass().getClassLoader());
    }

    @Override
    public void writeToParcel(Parcel dest, int flags) {
        dest.writeString(fragmentTag);
        dest.writeBundle(args);
    }

    protected final Fragment newFragment() {
        Fragment fragment = createFragment();
        Bundle oldArgs = fragment.getArguments();
        Bundle newArgs = new Bundle();
        if(oldArgs != null) {
            newArgs.putAll(oldArgs);
        }
        if(args != null) {
            newArgs.putAll(args);
        }
        fragment.setArguments(newArgs);
        return fragment;
    }

    protected abstract Fragment createFragment();
}

private ArrayList<FragmentIdentifier> fragmentIdentifiers = new ArrayList<>();

private FragmentTransaction currentTransaction = null;

private Fragment currentPrimaryItem = null;

public DynamicFragmentPagerAdapter(FragmentManager fragmentManager) {
    this.fragmentManager = fragmentManager;
}

private int findIndexIfAdded(FragmentIdentifier fragmentIdentifier) {
    for (int i = 0, size = fragmentIdentifiers.size(); i < size; i++) {
        FragmentIdentifier identifier = fragmentIdentifiers.get(i);
        if (identifier.fragmentTag.equals(fragmentIdentifier.fragmentTag)) {
            return i;
        }
    }
    return -1;
}

public void addFragment(FragmentIdentifier fragmentIdentifier) {
    if (findIndexIfAdded(fragmentIdentifier) < 0) {
        fragmentIdentifiers.add(fragmentIdentifier);
        notifyDataSetChanged();
    }
}

public void removeFragment(FragmentIdentifier fragmentIdentifier) {
    int index = findIndexIfAdded(fragmentIdentifier);
    if (index >= 0) {
        fragmentIdentifiers.remove(index);
        notifyDataSetChanged();
    }
}

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

@Override
public void startUpdate(@NonNull ViewGroup container) {
    if (container.getId() == View.NO_ID) {
        throw new IllegalStateException("ViewPager with adapter " + this
                + " requires a view id");
    }
}

@SuppressWarnings("ReferenceEquality")
@NonNull
@Override
public Object instantiateItem(@NonNull ViewGroup container, int position) {
    if (currentTransaction == null) {
        currentTransaction = fragmentManager.beginTransaction();
    }
    final FragmentIdentifier fragmentIdentifier = fragmentIdentifiers.get(position);
    // Do we already have this fragment?
    final String name = fragmentIdentifier.fragmentTag;
    Fragment fragment = fragmentManager.findFragmentByTag(name);
    if (fragment != null) {
        currentTransaction.attach(fragment);
    } else {
        fragment = fragmentIdentifier.newFragment();
        currentTransaction.add(container.getId(), fragment, fragmentIdentifier.fragmentTag);
    }
    if (fragment != currentPrimaryItem) {
        fragment.setMenuVisibility(false);
        fragment.setUserVisibleHint(false);
    }
    return fragment;
}

@Override
public void destroyItem(@NonNull ViewGroup container, int position, @NonNull Object object) {
    if (currentTransaction == null) {
        currentTransaction = fragmentManager.beginTransaction();
    }
    currentTransaction.detach((Fragment) object);
}

@SuppressWarnings("ReferenceEquality")
@Override
public void setPrimaryItem(@NonNull ViewGroup container, int position, @NonNull Object object) {
    Fragment fragment = (Fragment) object;
    if (fragment != currentPrimaryItem) {
        if (currentPrimaryItem != null) {
            currentPrimaryItem.setMenuVisibility(false);
            currentPrimaryItem.setUserVisibleHint(false);
        }
        fragment.setMenuVisibility(true);
        fragment.setUserVisibleHint(true);
        currentPrimaryItem = fragment;
    }
}

@Override
public void finishUpdate(@NonNull ViewGroup container) {
    if (currentTransaction != null) {
        currentTransaction.commitNowAllowingStateLoss();
        currentTransaction = null;
    }
}

@Override
public boolean isViewFromObject(@NonNull View view, @NonNull Object object) {
    return ((Fragment) object).getView() == view;
}

@Override
public Parcelable saveState() {
    Bundle bundle = new Bundle();
    bundle.putParcelableArrayList("fragmentIdentifiers", fragmentIdentifiers);
    return bundle;
}

@Override
public void restoreState(Parcelable state, ClassLoader loader) {
    Bundle bundle = ((Bundle)state);
    bundle.setClassLoader(loader);
    fragmentIdentifiers = bundle.getParcelableArrayList("fragmentIdentifiers");
}
}