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Recycler View double items on change fragment

I have a problem with the recyclerview in my app i have 2 fragments in the first one there is the recycler view which has to find the songs present in the device and put them in line in the second for now nothing. when I switch from one fragment to another the recycler view items double each time.
CODE:
HomeActvity
public class HomeActivity extends AppCompatActivity {
BottomNavigationView bottomNavigationView;
RecyclerView recyclerView;
TextView noMusicTextView;
HomeFragment homeFragment = new HomeFragment();
ProvaFragment provaFragment = new ProvaFragment();
#SuppressLint("MissingInflatedId")
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_home);
getSupportActionBar().hide();
noMusicTextView = findViewById(R.id.noSongs);
recyclerView = findViewById(R.id.recycler_view);
bottomNavigationView = findViewById(R.id.barra_navigazione);
getSupportFragmentManager().beginTransaction().replace(R.id.contenitore_frammenti, homeFragment).commit();
bottomNavigationView.setOnItemSelectedListener(new NavigationBarView.OnItemSelectedListener() {
#Override
public boolean onNavigationItemSelected(MenuItem item) {
switch (item.getItemId()) {
case R.id.home:
getSupportFragmentManager().beginTransaction().replace(R.id.contenitore_frammenti, homeFragment).commit();
return true;
case R.id.prova:
getSupportFragmentManager().beginTransaction().replace(R.id.contenitore_frammenti, provaFragment).commit();
return true;
}
return false;
}
});
}
}
HomeFragment
public class HomeFragment extends Fragment {
ArrayList<AudioModel> songsList = new ArrayList<>();
RecyclerView recyclerView;
TextView noMusicTextView;
#SuppressLint("MissingInflatedId")
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_home, container, false);
recyclerView = view.findViewById(R.id.recycler_view);
noMusicTextView = view.findViewById(R.id.noSongs);
String[] projection = {
MediaStore.Audio.Media.TITLE,
MediaStore.Audio.Media.DATA,
MediaStore.Audio.Media.DURATION,
};
String selection = MediaStore.Audio.Media.IS_MUSIC + " !=0";
Cursor cursor = getActivity().getContentResolver().query(MediaStore.Audio.Media.EXTERNAL_CONTENT_URI,projection,selection,null,null);
while(cursor.moveToNext()){
AudioModel songData = new AudioModel(cursor.getString(1), cursor.getString(0),cursor.getString(2));
if(new File(songData.getPath()).exists())
songsList.add(songData);
}
if(songsList.size() == 0){
noMusicTextView.setVisibility(View.VISIBLE);
}else{
recyclerView.setLayoutManager(new LinearLayoutManager(getActivity()));
recyclerView.setAdapter(new MusicListAdapter(songsList, getContext()));
}
return view;
}
}
MusicListAdapter
public class MusicListAdapter extends RecyclerView.Adapter<MusicListAdapter.ViewHolder>{
ArrayList<AudioModel> songsList;
Context context;
public MusicListAdapter(ArrayList<AudioModel> songsList, Context context) {
this.songsList = songsList;
this.context = context;
}
#Override
public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View view = LayoutInflater.from(context).inflate(R.layout.recycler_item,parent,false);
return new MusicListAdapter.ViewHolder(view);
}
#Override
public void onBindViewHolder(ViewHolder holder, int position) {
AudioModel songData = songsList.get(position);
holder.titleTextView.setText(songData.getTitle());
}
#Override
public int getItemCount() {
return songsList.size();
}
public class ViewHolder extends RecyclerView.ViewHolder{
TextView titleTextView;
ImageView iconImageView;
public ViewHolder(View itemView) {
super(itemView);
titleTextView = itemView.findViewById(R.id.music_title_text);
iconImageView = itemView.findViewById(R.id.icon_view);
}
}
}
I have tryed to use songsList.clear(); but this don't work(Sorry for my english).

When switching fragments, existing fragments aren't deleted.
Also, songsList isn't initialized; onViewCreated() is called at this time, so it seems that the transition adds the item to the songsList.
In order to solve the problem, it seems that it is necessary to do a good comparison so that the same item as the previously saved item is not added, or to not add an item every time in onViewCreated.

RecyclerView not updating on Fragment - Adapter shows null on notifyDataSetChanged()

I am trying to implement a sales app with 3 stages, whereby a user first adds the items, views the cart to checkout and prints a receipt. The first stage is done and works well. I am implementing this using one Activity with a tabbed layout and 3 fragments for each of the tabs.
On the activity for viewing the cart, I am using a RecyclerView which loads well when the activity is created, but once I add an item and try to view the list, there is no update. However, when I print the item list, the item has been added.
I have tried to update the RecyclerView using notifyDataSetChanged() but it gives me a null pointer exception. I have and tried several solutions but none has worked. Kindly assist.
Below is my code.
NewSaleActivity.java
public class NewSaleActivity extends AppCompatActivity implements NavigationView.OnNavigationItemSelectedListener {
private ActivityNewSaleBinding binding;
DrawerLayout drawerLayout;
NavigationView navigationView;
TabLayout tabLayout;
Context context;
ViewPager viewPager;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
binding = ActivityNewSaleBinding.inflate(getLayoutInflater());
setContentView(binding.getRoot());
Toolbar toolbar = findViewById(R.id.new_sale_toolbar);
toolbar.setTitle(R.string.new_sale);
setSupportActionBar(toolbar);
drawerLayout = findViewById(R.id.new_sale_drawer);
navigationView = findViewById(R.id.new_sale_navigation);
navigationView.bringToFront();
navigationView.setNavigationItemSelectedListener(this);
navigationView.setCheckedItem(R.id.nav_sale);
ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(this, drawerLayout, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
drawerLayout.addDrawerListener(toggle);
toggle.setDrawerIndicatorEnabled(true);
toggle.syncState();
context = getApplicationContext();
tabLayout = findViewById(R.id.tab_layout);
SectionsPagerAdapter sectionsPagerAdapter = new SectionsPagerAdapter(this, getSupportFragmentManager());
viewPager = binding.viewPager;
viewPager.setAdapter(sectionsPagerAdapter);
viewPager.setOffscreenPageLimit(1);
TabLayout tabs = binding.tabLayout;
tabs.setupWithViewPager(viewPager);
viewPager.addOnPageChangeListener(new TabLayout.TabLayoutOnPageChangeListener(tabLayout));
tabLayout.addOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {
#Override
public void onTabSelected(TabLayout.Tab tab) {
//When cart tab is selected
if(tab.getPosition() == 1) {
CartFragment cartFragment = new CartFragment();
cartFragment.loadItemsInCart();
}
}
#Override
public void onTabUnselected(TabLayout.Tab tab) {
}
#Override
public void onTabReselected(TabLayout.Tab tab) {
}
});
}
#Override
public boolean onNavigationItemSelected(#NonNull MenuItem item) {
switch (item.getItemId()) {
case R.id.nav_home:
Intent mainIntent = new Intent(NewSaleActivity.this, MainActivity.class);
startActivity(mainIntent);
finish();
break;
case R.id.nav_inventory:
Intent inventoryIntent = new Intent(NewSaleActivity.this, InventoryActivity.class);
startActivity(inventoryIntent);
finish();
break;
case R.id.nav_sale:
break;
case R.id.nav_logout:
UserLogout.userLogout(NewSaleActivity.this);
break;
}
drawerLayout.closeDrawer(GravityCompat.START);
return true;
}
}
CartFragment.java
public class CartFragment extends Fragment {
RecyclerView cartRecyclerView;
TextInputLayout grossTotalInput, discountInput, netTotalInput;
Button checkoutButton;
CartItemAdapter cartItemAdapter;
ArrayList<CartItem> cartItemList;
public CartFragment() {
// Required empty public constructor
}
public static CartFragment newInstance() {
CartFragment fragment = new CartFragment();
Bundle args = new Bundle();
return fragment;
}
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
#Override
public void onViewCreated(#NonNull View view, #Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
cartRecyclerView = view.findViewById(R.id.cart_recycler_view);
grossTotalInput = view.findViewById(R.id.gross_total_input);
discountInput = view.findViewById(R.id.discount_input);
netTotalInput = view.findViewById(R.id.net_total_input);
checkoutButton = view.findViewById(R.id.checkout_button);
Paper.init(requireContext());
cartItemList = Paper.book().read("cartItems", new ArrayList<CartItem>());
cartRecyclerView.setLayoutManager(new LinearLayoutManager(getContext()));
cartItemAdapter = new CartItemAdapter(cartItemList);
cartRecyclerView.setAdapter(cartItemAdapter);
checkoutButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
checkoutOrder();
}
});
cartItemAdapter.notifyDataSetChanged();
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
return inflater.inflate(R.layout.fragment_cart, container, false);
}
public void loadItemsInCart() {
ArrayList<CartItem> cartList = Paper.book().read("cartItems", new ArrayList<CartItem>());
for(CartItem cartItem : cartList) {
Log.d("cartItem", cartItem.getItemName());
}
cartItemAdapter.updateCartList(cartList);
Log.d("loadItemsInCart", "Load Items In Cart is triggered");
}
CartItemAdapter.java
public class CartItemAdapter extends RecyclerView.Adapter<CartItemAdapter.ViewHolder> {
private final ArrayList<CartItem> cartItems;
public CartItemAdapter(ArrayList<CartItem> cartItems) {
this.cartItems = cartItems;
}
public static class ViewHolder extends RecyclerView.ViewHolder {
public TextView itemCode, itemName, quantity, price;
public ViewHolder(View itemView) {
super(itemView);
this.itemCode = itemView.findViewById(R.id.item_code);
this.itemName = itemView.findViewById(R.id.item_name);
this.quantity = itemView.findViewById(R.id.item_quantity);
this.price = itemView.findViewById(R.id.item_price);
}
}
#NonNull
#Override
public ViewHolder onCreateViewHolder(#NonNull ViewGroup parent, int viewType) {
LayoutInflater layoutInflater = LayoutInflater.from(parent.getContext());
View cartListItem = layoutInflater.inflate(R.layout.add_to_cart_item, parent, false);
return new CartItemAdapter.ViewHolder(cartListItem);
}
#Override
public void onBindViewHolder(#NonNull ViewHolder holder, int position) {
holder.itemCode.setText(cartItems.get(position).getItemCode());
holder.itemName.setText(cartItems.get(position).getItemName());
holder.quantity.setText(cartItems.get(position).getQuantity().toString());
holder.price.setText(cartItems.get(position).getTotalAmount().toString());
}
#Override
public int getItemCount() {
return cartItems.size();
}
#SuppressLint("NotifyDataSetChanged")
public void updateCartList(ArrayList<CartItem> cartList) {
cartItems.clear();
this.cartItems.addAll(cartList);
notifyDataSetChanged();
}
}
The error message that I get is as below
java.lang.NullPointerException: Attempt to invoke virtual method 'void app.project.jsml_sales_app.adapters.CartItemAdapter.updateCartList(java.util.ArrayList)' on a null object reference
at app.project.jsml_sales_app.activities.fragments.CartFragment.loadItemsInCart(CartFragment.java:128)
at app.project.jsml_sales_app.activities.NewSaleActivity$1.onTabSelected(NewSaleActivity.java:78)
at com.google.android.material.tabs.TabLayout.dispatchTabSelected(TabLayout.java:1993)
at com.google.android.material.tabs.TabLayout.selectTab(TabLayout.java:1986)

RecyclerView: No adapter attached; skipping layout? What should I do? [duplicate]

This question already has answers here:
recyclerview No adapter attached; skipping layout
(38 answers)
Closed 4 years ago.
Today I'm having this issue with my application; I want to say that I read almost ALL the other questions here on StackOverflow but nothing, always the same problem.
homepage.java (main class)
public class homepage extends AppCompatActivity {
private SectionsPagerAdapter mSectionsPagerAdapter;
private ViewPager mViewPager;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_homepage);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager());
mViewPager = (ViewPager) findViewById(R.id.container);
mViewPager.setAdapter(mSectionsPagerAdapter);
TabLayout tabLayout = (TabLayout) findViewById(R.id.tabs);
mViewPager.addOnPageChangeListener(new TabLayout.TabLayoutOnPageChangeListener(tabLayout));
tabLayout.addOnTabSelectedListener(new TabLayout.ViewPagerOnTabSelectedListener(mViewPager));
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.menu_homepage, menu);
return true;
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
int id = item.getItemId();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
public static class PlaceholderFragment extends Fragment {
private static final String ARG_SECTION_NUMBER = "section_number";
public PlaceholderFragment() {
}
public static PlaceholderFragment newInstance(int sectionNumber) {
PlaceholderFragment fragment = new PlaceholderFragment();
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 = null;
switch(getArguments().getInt(ARG_SECTION_NUMBER))
{
case 1:
rootView = inflater.inflate(R.layout.fragment_homepage, container, false);
break;
case 2:
rootView = inflater.inflate(R.layout.fragment_fibra, container, false);
break;
case 3:
rootView = inflater.inflate(R.layout.fragment_adsl, container, false);
break;
case 4:
rootView = inflater.inflate(R.layout.fragment_aiuto, container, false);
break;
}
return rootView;
}
}
public class SectionsPagerAdapter extends FragmentPagerAdapter {
public SectionsPagerAdapter(FragmentManager fm) {
super(fm);
}
#Override
public Fragment getItem(int position) {
return PlaceholderFragment.newInstance(position + 1);
}
#Override
public int getCount() {
// Show 4 total pages.
return 4;
}
}
}
MyAdapter.java (default code from Android Studio Guide)
public class MyAdapter extends RecyclerView.Adapter<MyAdapter.MyViewHolder>
{
private String[] mDataset;
public static class MyViewHolder extends RecyclerView.ViewHolder {
public TextView mTextView;
public MyViewHolder(TextView v) {
super(v);
mTextView = v;
}
}
public MyAdapter(String[] myDataset) {
mDataset = myDataset;
}
#Override
public MyAdapter.MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
TextView v = (TextView) LayoutInflater.from(parent.getContext()).inflate(android.R.layout.simple_list_item_1, parent, false);
MyViewHolder vh = new MyViewHolder(v);
return vh;
}
#Override
public void onBindViewHolder(MyViewHolder holder, int position) {
holder.mTextView.setText(mDataset[position]);
}
#Override
public int getItemCount() {
return mDataset.length;
}
}
And finally, one of the fragment that I'm using:
fibra.java
public class fibra extends Fragment {
private static final String ARG_PARAM1 = "param1";
private static final String ARG_PARAM2 = "param2";
private String mParam1;
private String mParam2;
private OnFragmentInteractionListener mListener;
private RecyclerView recyclerView;
private MyAdapter adapter;
private LinearLayoutManager llm;
String [] prova={"prova1","prova2","prova2","prova2","prova2","prova2","prova2"};
public fibra() {
}
public static fibra newInstance(String param1, String param2) {
fibra fragment = new fibra();
Bundle args = new Bundle();
args.putString(ARG_PARAM1, param1);
args.putString(ARG_PARAM2, param2);
fragment.setArguments(args);
return fragment;
}
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//setContentView(R.layout.my_activity); (doesn't work "cannot resolve method")
recyclerView.setHasFixedSize(true); //per migliorare performance
llm = new LinearLayoutManager(getActivity());
llm.setOrientation(LinearLayoutManager.VERTICAL);
recyclerView.setLayoutManager(llm);
adapter = new MyAdapter(prova);
recyclerView.setAdapter(adapter);
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_fibra, container, false);
return rootView;
}
// TODO: Rename method, update argument and hook method into UI event
public void onButtonPressed(Uri uri) {
if (mListener != null) {
mListener.onFragmentInteraction(uri);
}
}
#Override
public void onAttach(Context context) {
super.onAttach(context);
if (context instanceof OnFragmentInteractionListener) {
mListener = (OnFragmentInteractionListener) context;
} else {
throw new RuntimeException(context.toString()
+ " must implement OnFragmentInteractionListener");
}
}
#Override
public void onDetach() {
super.onDetach();
mListener = null;
}
public interface OnFragmentInteractionListener {
void onFragmentInteraction(Uri uri);
}
}

Here:
//setContentView(R.layout.my_activity); (doesn't work "cannot resolve method")
It's like inflating a layout inside an Activity which you already have onCreateView and in a Fragment.
Change the first codes to :
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
Then, initialize RecyclerView inside onCreateView().
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_fibra, container, false);
// Here you should initialize RecyclerView and other widgets by rootView.findViewById and etc
recyclerView = (RecyclerView) rootView.findViewById(R.id.recyclerView);
recyclerView.setHasFixedSize(true); //per migliorare performance
llm = new LinearLayoutManager(getActivity());
llm.setOrientation(LinearLayoutManager.VERTICAL);
recyclerView.setLayoutManager(llm);
adapter = new MyAdapter(prova);
recyclerView.setAdapter(adapter);
return rootView;
}

You forget to add tablaylout.setupWithViewPager(mViewPager); in your homepage.java

Why when switching fragments, recyclerview is lost?

Hello I am newbie in java programming(android). Currently I learn recyclerview use volley in fragments and need help. why when switching fragment one to fragment two and when back to fragment one, recycleview lost? even though at the beginning recyleview available? thanks for help
this is backgroundtask.java
Context mContext;
ArrayList<List> mArrayList = new ArrayList<>();
String json_url = "http://192.168.43.215/belajar/contact_mad.php";
private static final String TAG = "BackgroundTask";
public BackgroundTask(Context context) {
this.mContext = context;
}
public ArrayList<List> getList()
{
JsonArrayRequest jsonArrayRequest = new JsonArrayRequest(Request.Method.POST, json_url, (String) null,
new Response.Listener<JSONArray>() {
#Override
public void onResponse(JSONArray response) {
int count = 0;
while (count<response.length())
{
try {
JSONObject jsonObject = response.getJSONObject(count);
List list = new List(jsonObject.getString("Id"),jsonObject.getString("ImageUrl"),jsonObject.getString("Name"));
mArrayList.add(list);
count++;
} catch (JSONException e) {
e.printStackTrace();
}
}
}
}, new Response.ErrorListener() {
#Override
public void onErrorResponse(VolleyError error) {
Toast.makeText(mContext,"Errorr.............",Toast.LENGTH_SHORT).show();
error.printStackTrace();
}
}
);
MySingleton.getInstance(mContext).addToRequestQue(jsonArrayRequest);
Log.e(TAG, "Log Dari background");
return mArrayList;
}
this is recycleradapter.java
public class RecyclerAdapter extends RecyclerView.Adapter<RecyclerAdapter.MyViewHolder> {
ArrayList<List> mArrayList = new ArrayList<>();
private static final String TAG = "RecyclerAdapter";
public RecyclerAdapter(ArrayList<List> arrayList){
this.mArrayList = arrayList;
}
#Override
public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.row_item,parent,false);
MyViewHolder myViewHolder = new MyViewHolder(view);
return myViewHolder;
}
#Override
public void onBindViewHolder(MyViewHolder holder, int position) {
final String name = mTxtName.getText().toString();
final String email = mTxtEmail.getText().toString();
final String nameFood = this.mArrayList.get(position).getName();
final String imageUrl = this.mArrayList.get(position).getImageUrl();
holder.Name.setText(mArrayList.get(position).getName());
final Context context = holder.mImageView.getContext();
Picasso.with(context).load(mArrayList.get(position).getImageUrl()).into(holder.mImageView);
Log.e(TAG, "Log Dari On BindView");
holder.cvMain.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
/*Intent intent = new Intent(v.getContext(),ActivityClick.class);
Bundle bundle = new Bundle();
bundle.putString("imageUrl",imageUrl);
bundle.putString("name",name);
intent.putExtras(bundle);
v.getContext().startActivity(intent);*/
Toast.makeText(context, name, Toast.LENGTH_LONG).show();
}
});
}
#Override
public int getItemCount() {
return mArrayList.size();
}
public static class MyViewHolder extends RecyclerView.ViewHolder{
TextView Name;
RelativeLayout cvMain;
ImageView mImageView;
public MyViewHolder(View itemView) {
super(itemView);
mImageView = (ImageView) itemView.findViewById(R.id.imageView);
Name = (TextView)itemView.findViewById(R.id.txtName);
cvMain = (RelativeLayout) itemView.findViewById(R.id.cvMain);
}
}
this is MainMenu.java
public class MainMenu extends AppCompatActivity
implements NavigationView.OnNavigationItemSelectedListener {
public static TextView mTxtName, mTxtEmail;
private Fragment fragment;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main_menu);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
drawer.setDrawerListener(toggle);
toggle.syncState();
NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
navigationView.setNavigationItemSelectedListener(this);
mTxtName = (TextView)navigationView.getHeaderView(0).findViewById(R.id.txtNavName);
mTxtEmail = (TextView)navigationView.getHeaderView(0).findViewById(R.id.txtNavEmail);
Bundle bundle = getIntent().getExtras();
mTxtName.setText(bundle.getString("name"));
mTxtEmail.setText(bundle.getString("email"));
android.support.v4.app.FragmentManager fm = getSupportFragmentManager();
android.support.v4.app.FragmentTransaction transaction = fm.beginTransaction();
transaction.replace(R.id.tempatfragment, new ListMakanan()).addToBackStack(null).commit();
}
#Override
public void onBackPressed() {
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
if (drawer.isDrawerOpen(GravityCompat.START)) {
drawer.closeDrawer(GravityCompat.START);
} else {
super.onBackPressed();
}
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main_menu, menu);
return true;
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.cara_pesan) {
return true;
}else if(id == R.id.keluar){
finish();
return true;
}
return super.onOptionsItemSelected(item);
}
#SuppressWarnings("StatementWithEmptyBody")
#Override
public boolean onNavigationItemSelected(MenuItem item) {
// Handle navigation view item clicks here.
int id = item.getItemId();
android.support.v4.app.FragmentManager fm = getSupportFragmentManager();
android.support.v4.app.FragmentTransaction transaction = fm.beginTransaction();
if (id == R.id.list_makanan) {
transaction.replace(R.id.tempatfragment, new ListMakanan()).addToBackStack(null).commit();
} else if (id == R.id.pesan_makanan) {
transaction.replace(R.id.tempatfragment, new PesanMakanan()).addToBackStack(null).commit();
}
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
drawer.closeDrawer(GravityCompat.START);
return true;
}
this is fragment ListMakanan.java
public class ListMakanan extends Fragment {
RecyclerView mRecyclerView;
RecyclerView.Adapter mAdapter;
RecyclerView.LayoutManager mLayoutManager;
ArrayList<List> mArrayList = new ArrayList<>();
private static final String TAG = "ListMakanan";
public ListMakanan() {
// Required empty public constructor
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
return inflater.inflate(R.layout.fragment_list__makanan, container, false);
}
#Override
public void onViewCreated(View view, #Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
mRecyclerView = (RecyclerView)view.findViewById(R.id.recyclervView);
mLayoutManager = new LinearLayoutManager(getActivity());
mRecyclerView.setLayoutManager(mLayoutManager);
mRecyclerView.setHasFixedSize(true);
BackgroundTask backgroundTask = new BackgroundTask(getActivity());
mArrayList = backgroundTask.getList();
mAdapter = new RecyclerAdapter(mArrayList);
mRecyclerView.setAdapter(mAdapter);
Log.e(TAG, "Log Dari View Created");
}

Whenever you use replace on your FragmentManager to switch fragments you are doing a remove(remove any fragments from container) followed by an add(the new fragment). This wipes out the state of the previous fragment and forces a refresh when you go back, to avoid this you can just call add fragment instead of replace.

How to stop tab change from running fragment onCreateView in Andriod

I have three tabs using the implementation below and they perform very well. When tab is changed the proper fragment is load and so on. The problem is that, when i get to the last tab and comeback to the first fragment, its like its oncreateview method is always triggered again running the other codes it in causing duplicates. Any help will be greatly appreciated.
//Activity on the tab is based
public class Dashboard extends AppCompatActivity {
private TabLayout tabLayout;
private ViewPager viewPager;
private MyViewPagerAdapter myViewPagerAdapter;
private int[] tabIcon = {R.drawable.ic_home, R.drawable.ic_message, R.drawable.ic_person};
android.support.v7.widget.Toolbar toolbar;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.dashboard);
//Toolbar
toolbar = (android.support.v7.widget.Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
//ViewPager
viewPager = (ViewPager) findViewById(R.id.viewpager);
setupViewPager(viewPager);
//Tablayout
tabLayout = (TabLayout) findViewById(R.id.tabs);
tabLayout.setupWithViewPager(viewPager);
tabLayout.getTabAt(0).setIcon(tabIcon[0]);
tabLayout.getTabAt(1).setIcon(tabIcon[1]);
tabLayout.getTabAt(2).setIcon(tabIcon[2]);
viewPager.addOnPageChangeListener(new TabLayout.TabLayoutOnPageChangeListener(tabLayout));
tabLayout.setOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {
#Override
public void onTabSelected(TabLayout.Tab tab) {
switch(tab.getPosition()) {
case 0:
viewPager.setCurrentItem(0);
toolbar.setTitle("Home");
break;
case 1:
viewPager.setCurrentItem(1);
toolbar.setTitle("Messages");
break;
case 2:
viewPager.setCurrentItem(2);
toolbar.setTitle("Profile");
break;
}
}
#Override
public void onTabUnselected(TabLayout.Tab tab) {
}
#Override
public void onTabReselected(TabLayout.Tab tab) {
}
});
}
private void setupViewPager(ViewPager viewPager){
myViewPagerAdapter = new MyViewPagerAdapter(getSupportFragmentManager());
myViewPagerAdapter.addFragments(new CategoryFragment(), "Categories");
myViewPagerAdapter.addFragments(new MessagesFragment(), "Messages");
myViewPagerAdapter.addFragments(new ProfileFragment(), "Profile");
viewPager.setAdapter(myViewPagerAdapter);
}
//View Pager Adapter
public class MyViewPagerAdapter extends FragmentPagerAdapter {
ArrayList<Fragment> fragments = new ArrayList<>();
ArrayList<String> tabTitles = new ArrayList<>();
public void addFragments(Fragment fragments, String titles){
this.fragments.add(fragments);
this.tabTitles.add(titles);
}
public MyViewPagerAdapter(FragmentManager fm) {
super(fm);
}
#Override
public int getCount() {
return fragments.size();
}
#Override
public Fragment getItem(int position) {
return fragments.get(position);
}
#Override
public CharSequence getPageTitle(int position) {
//return tabTitles.get(position);
return null;
}
}
#Override
public void onBackPressed() {
super.onBackPressed();
}
}
//Main first fragment code
public class CategoryFragment extends Fragment {
private DBHandler dbHandler;
private ListView listView;
private ListAdapter adapter;
ArrayList<Categories> categoriesList = new ArrayList<Categories>();
public CategoryFragment() {
// Required empty public constructor
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
// Inflate the layout for this fragment
View view = inflater.inflate(R.layout.fragment_home, container, false);
//Setting up the basic categories
dbHandler = new DBHandler(view.getContext());
//Get Categories from database
final Cursor cursor = dbHandler.getCategories(0);
if (cursor != null) {
if(cursor.moveToFirst()){
do{
Categories categories = new Categories();
categories.set_id(cursor.getInt(0));
categories.set_categoryname(cursor.getString(2));
categories.set_categoriescaption(cursor.getString(3));
categoriesList.add(categories);
}while (cursor.moveToNext());
}
cursor.close();
}
listView = (ListView) view.findViewById(R.id.categories);
adapter = new CategoryAdapter(view.getContext(), R.layout.cursor_row, categoriesList);
listView.setAdapter(adapter);
listView.setOnItemClickListener(
new AdapterView.OnItemClickListener() {
#Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
Integer cid = (int) (long) adapter.getItemId(position);
TextView categoryname = (TextView) view.findViewById(R.id.cursor);
String cname = categoryname.getText().toString();
Intent i = new Intent(view.getContext(), CategoryList.class);
i.putExtra("categoryname", cname);
i.putExtra("categoryid", cid);
startActivity(i);
}
}
);
return view;
}
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
}
So when i swipe back here from the last tab. OncreateView runs again. How can i handle that and prevent duplicates. Thank you

By defaults ViewPager retains only 1 page in the view hierarchy in an idle state.So when you swipe to third tab the viepager destroys the first tab in order to retain the second one.
To solve this issue add this line
viewPager.setOffscreenPageLimit(3);
after you set your adapter.
Check here the documentation for more