Develop Reference

Firebase add new child when an item on adapter is non-zero

Hello so I have a function in an app where you will add a data from the adapter if the quantity is non-zero and it will be saved to the firebase realtime database. What i wanna do is if the other item in adapter is non-zero it will add a child to the database but instead firebase is just replacing the item instead of adding a new child what should i do?
here is the code
public class UsualFragRViewAdapter extends RecyclerView.Adapter <UsualFragRViewAdapter.ViewHolder> {
private List<FragmentsUsualModels> items;
private Context context;
public UsualFragRViewAdapter( Context context,List<FragmentsUsualModels> items ) {
this.context = context;
this.items = items;
}
#NonNull
#Override
public ViewHolder onCreateViewHolder(#NonNull ViewGroup parent, int viewType) {
View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.fragment_usual_array, parent, false);
ViewHolder holder = new ViewHolder(view);
return holder;
}
#Override
public void onBindViewHolder(#NonNull final ViewHolder holder, final int position) {
final FragmentsUsualModels arrayitems = items.get(position);
holder.itemName.setText(arrayitems.getItemName());
holder.price.setText(String.valueOf("$ " +arrayitems.getPrice()));
holder.quantity.setNumber(arrayitems.getQuantity());
holder.card.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
}
});
holder.quantity.setOnValueChangeListener(new ElegantNumberButton.OnValueChangeListener() { //all items are located in its positions
#Override
public void onValueChange(ElegantNumberButton view, int oldValue, int newValue) { //Need to pass all non-zero items as chatview
arrayitems.setQuantity(String.valueOf(newValue));
if (newValue !=0){
String datavalue = holder.itemName.getText().toString();
String dataprice = holder.price.getText().toString();
String dataquantity = holder.quantity.getNumber().toString();
DatabaseReference data = FirebaseDatabase.getInstance().getReference("itemdata");
data.child("dataname").setValue(datavalue);
data.child("dataprice").setValue(dataprice);
data.child("dataquantity").setValue(dataquantity);
Log.d(TAG, "the new value of this data is: " +dataquantity);
Log.d(TAG, "the itemname of this position is: "+datavalue);
Log.d(TAG, "the price of this item in this position is: " +dataprice);
}
Log.d(TAG, "user changed the quantity in this position to " +arrayitems);
}
});
}
#Override
public int getItemCount() {
return items.size();
}
public class ViewHolder extends RecyclerView.ViewHolder {
CardView card;
ImageView image;
TextView itemName;
TextView price;
ElegantNumberButton quantity;
Button donebtn;
public ViewHolder(#NonNull View itemView) {
super(itemView);
card = itemView.findViewById(R.id.ucard);
image = itemView.findViewById(R.id.uimage);
itemName = itemView.findViewById(R.id.uitemName);
price = itemView.findViewById(R.id.uprice);
quantity = itemView.findViewById(R.id.uquantity);
donebtn = itemView.findViewById(R.id.udonebtn);
}
}
}

If you want to generate a new child node under a location, call push() on that DatabaseReference. So to create a new child node under itemdata:
DatabaseReference data = FirebaseDatabase.getInstance().getReference("itemdata");
DatabaseReference newData = data.push();
Now you can write the data to this new location as:
newData.child("dataname").setValue(datavalue);
newData.child("dataprice").setValue(dataprice);
newData.child("dataquantity").setValue(dataquantity);
One additional change to consider is the reducing the number of writes. Your current code does a separate setValue() call for each property. This works, but it means that any listeners will get called three times, once for each property.
While this may be what you want, it is quite common to want these writes to appear as one operation. If that is the case, you can perform a single setValue() with:
Map<String,Object> values = new HashMap<>();
values.put("dataname", datavalue);
values.put("dataprice", dataprice);
values.put("dataquantity", dataquantity);
newData.setValue(values);
The end result will be exactly the same as before, but now with a single write operation.

You should use push() to create unique id for database item
dataBase.child(/*CHILD*/).push().setValue(dataValue);

Getting a null object exception when using an interface

I have created a shopping cart via recyclerview. Each viewholder also has a + and - button to add or remove quantity. This functionality is done in the adapter and I have to notify the parent fragment of the updated total amount. This last bit is done via an interface. The problem is, I am getting the following error:
Process: com.ecomm.market, PID: 6630
java.lang.NullPointerException: Attempt to invoke interface method 'void com.ecomm.market.SelectionAdapter$OnUpdateCartListener.onUpdateCart(int)' on a null object reference
at com.ecomm.market.SelectionAdapter$ViewHolder$1.onClick(SelectionAdapter.java:103)
at android.view.View.performClick(View.java:5637)
at android.view.View$PerformClick.run(View.java:22429)
at android.os.Handler.handleCallback(Handler.java:751)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6119)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
The selected item and corresponding quantity are stored in a hashmap that I convert to an array to populate the recycler view cart. This is what the relevant part of my main fragment MenuFragment looks like:
// Using the adapter interface to add items to cart and adding up total amount
menuItemAdapter.setOnAddToCartListener(new MenuItemAdapter.OnAddToCartListener() {
#Override
public void onAddToCart(final HashMap selectionItemsHashMap) {
setupSelectionRecycler(menuView);
totalAmount = mapToArray(selectionItemsHashMap);
selectionAdapter = new SelectionAdapter(selectionItemArrayList, selectionItemsHashMap, totalAmount);
selectionRecycler.setAdapter(selectionAdapter);
cartItemsHashmap = selectionItemsHashMap;
selectionAdapter.setUpdateCartListener(new SelectionAdapter.OnUpdateCartListener() {
#Override
public void onUpdateCart(int updatedTotalAmount) {
String stringTotalAmount = Integer.toString(updatedTotalAmount);
Log.d(TAG, "received total:" +stringTotalAmount);
tvTotalAmount.setText("$"+ stringTotalAmount);
totalAmount = updatedTotalAmount;
}
});
}
});
}
And here is an excerpt from my adapter SelectionAdapter:
public class SelectionAdapter extends RecyclerView.Adapter<SelectionAdapter.ViewHolder> {
private static final String TAG = SelectionAdapter.class.getSimpleName();
private ArrayList<SelectionItem> selectionItemArrayList = new ArrayList<>();
public HashMap<String, Integer> selectionItemsHashMap = new HashMap<String, Integer>();
public int totalAmount;
private OnUpdateCartListener updateCartListener;
public interface OnUpdateCartListener {
void onUpdateCart(int totalAmount);
}
public void setUpdateCartListener(OnUpdateCartListener updateCartListener) {
this.updateCartListener = updateCartListener;
}
public SelectionAdapter(ArrayList<SelectionItem> selectionItemArrayList, HashMap<String, Integer> selectionItemsHashMap, int currentTotalAmount) {
this.selectionItemArrayList = selectionItemArrayList;
this.selectionItemsHashMap = selectionItemsHashMap;
this.totalAmount = currentTotalAmount;
}
#NonNull
#Override
public ViewHolder onCreateViewHolder(#NonNull ViewGroup viewGroup, int viewType) {
View view = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.selection_card, viewGroup, false);
ViewHolder viewHolder = new ViewHolder(view);
return viewHolder;
}
#Override
public void onBindViewHolder(#NonNull ViewHolder viewHolder, int position) {
viewHolder.tvSelectItem.setText(selectionItemArrayList.get(position).getSelectionName());
String quantity = Integer.toString(selectionItemArrayList.get(position).getSelectionQuantity());
viewHolder.tvDishQuantity.setText(quantity);
}
#Override
public int getItemCount() {
return selectionItemArrayList.size();
}
public class ViewHolder extends RecyclerView.ViewHolder {
TextView tvSelectItem, tvDishQuantity;
ImageView addQuantity, subtractQuantity, deleteItem;
public ViewHolder(#NonNull View itemView) {
super(itemView);
tvSelectItem = itemView.findViewById(R.id.dish_selection);
tvDishQuantity = itemView.findViewById(R.id.dish_quantity);
addQuantity = itemView.findViewById(R.id.button_add);
subtractQuantity = itemView.findViewById(R.id.button_subtract);
deleteItem = itemView.findViewById(R.id.delete_item);
addQuantity.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
// Find the name of the menu item
int position = getAdapterPosition();
String itemName = selectionItemArrayList.get(position).getSelectionName();
// Increase quantity
int currentQuantity = selectionItemsHashMap.get(itemName);
currentQuantity += 1;
// Update the hashmap with the new quantity
selectionItemsHashMap.put(itemName,currentQuantity);
//Update total amount
for (Object name: selectionItemsHashMap.keySet()) {
String key = (String) name;
if (key.equals(selectionItemArrayList.get(position).getSelectionName())) {
int eachPrice = Integer.parseInt(selectionItemArrayList.get(position).getSelectionPrice());
totalAmount += eachPrice;
}
}
// Display the new quantity
String stringCurrentQuantity = Integer.toString(currentQuantity);
tvDishQuantity.setText(stringCurrentQuantity);
//updateCartListener.onUpdateCart(totalAmount);
}
});
}
EDIT
A couple of points:
- When the cart is initially filled, I use this same code and it works fine.
- The problem occurs once the user returns to the cart and I have to repopulate it from a bundle. Everything works fine, except when the user goes straight to the cart and attempts to alter the quantity from there.

Pass interface implementation into the constructor of Adapter as follows :
public SelectionAdapter(ArrayList<SelectionItem> selectionItemArrayList, HashMap<String, Integer> selectionItemsHashMap, int currentTotalAmount,UpdateCartListener updateCartListener ) {
this.selectionItemArrayList = selectionItemArrayList;
this.selectionItemsHashMap = selectionItemsHashMap;
this.totalAmount = currentTotalAmount;
this.updateCartListener = updateCartListener
}
This will provide an implementation of your interface on the initialization of your adapter so it will be not null when you are using it for update cart.

So you try to access the listener inside the ViewHolder which is probably the cause of the crash, what the standard way is setting the OnClickListener inside your adapter
#Override
public void onBindViewHolder(#NonNull ViewHolder viewHolder, int position) {
viewHolder.tvSelectItem.setText(selectionItemArrayList.get(position).getSelectionName());
String quantity = Integer.toString(selectionItemArrayList.get(position).getSelectionQuantity());
viewHolder.tvDishQuantity.setText(quantity);
viewHolder.addQuantity.setOnClickListener(new View.OnClickListener() {
...
}
}

You need to instantiate your updateCartListener begfore you use it. Do updateCartListener = new WhatverClassThatImplementsYourInterafce() before you use it or make your method to override Default if you are using Java 8 using the new FunctionalInterface in java.util.Function.

I guess you forget assignment the updateCartListener in your adapter.
SelectionAdapter(selectionItemArrayList, selectionItemsHashMap, totalAmount);
cartItemsHashmap = selectionItemsHashMap;
selectionAdapter.setUpdateCartListener(new SelectionAdapter.OnUpdateCartListener() {
#Override
public void onUpdateCart(int updatedTotalAmount) {
String stringTotalAmount = Integer.toString(updatedTotalAmount);
Log.d(TAG, "received total:" +stringTotalAmount);
tvTotalAmount.setText("$"+ stringTotalAmount);
totalAmount = updatedTotalAmount;
}
});
selectionRecycler.setAdapter(selectionAdapter);

android fragment to fragment communication : update recyclerView of the ReceiverFragment via interface

I have two fragments and I am trying to update the recyclerView of the ReceiverFragment via interface. Both fragments have its own adapter (SenderAdapter and ReceiverAdapter).
I have to mention that I also have two SQLDatabase, where group.db is used to populate the SenderFragment and client.db is used to populate the ReceiverFragment.
But ReceiverFragment will only be populate if a CheckBox is ticked in the SenderAdapter.
All the communication between the fragments is ok. When I tick a CheckBox, The SenderAdapter sends a message to MainActivity and the MainActivity sends the same message to ReceiverFragment.
This is SenderFragment:
This would be the desired result.
When I use the message from interface to read the client.db, I get the nullException.
This is the ReceiverFragment:
public class ReceiverFragment extends Fragment {
View view;
private RecyclerView mClientList;
private RecyclerView.Adapter mClientListAdapter;
private RecyclerView.LayoutManager mClientListLayoutManager;
private String receivedFromSender;
ArrayList<ClientObject> clientList;
SQLiteDatabase clientListTable;
ClientRepository clientRepository;
private static String rootPath = Environment.getExternalStorageDirectory()+"/PassKeyBF/";
public ReceiverFragment() {
// Required empty public constructor
}
public String getMessageFromSender(String message){
if (message != null) {
receivedFromSender = message;
Log.i("debinf recfrag", "message from sender (function) is : " + receivedFromSender);
//Log.i("debinf recgfrag", "mContext in interface : " + mContext);
if (message != null) {
if (new File(rootPath + receivedFromSender, "client.db").isFile()) {
clientReading(message);
}
}
}
return null;
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
view = inflater.inflate(R.layout.fragment_receiver, container, false);
// If I use mContext instead of getContext(), I get rid of the context error showed below.
//mContext = getContext();
clientList = new ArrayList<>();
initializeRecyclerView();
//clientReading("-LWBPaM7RA9UOcUVty79");
return view;
}
private void clientReading(String pathToClientTable) {
if (new File(rootPath + pathToClientTable, "client.db").isFile()) {
Log.i("debinf recgfrag", "mContext in clientReading" + mContext);
ClientDatabaseHelper clientDatabaseHelper = new ClientDatabaseHelper(mContext,"client.db", rootPath+pathToClientTable+"/");
clientListTable = clientDatabaseHelper.getReadableDatabase();
clientRepository = new ClientRepository(clientListTable);
clientList = clientRepository.SearchAllClients();
Log.i("debinf recfrag", "clientList in clientReading is " + clientList.get(0).getName());
mClientListAdapter = new ReceiverAdapter(mContext,clientList);
mClientList.setAdapter(mClientListAdapter);
//mClientListAdapter.notifyDataSetChanged();
}
}
private void initializeRecyclerView() {
mClientList = (RecyclerView) view.findViewById(R.id.clientList);
mClientList.setNestedScrollingEnabled(false);
mClientList.setHasFixedSize(false);
mClientListLayoutManager = new LinearLayoutManager(mContext,LinearLayout.VERTICAL,false);
mClientList.setLayoutManager(mClientListLayoutManager);
mClientListAdapter = new ReceiverAdapter(mContext,clientList);
mClientList.setAdapter(mClientListAdapter);
}
}
This is the ReceiverAdapter
public class ReceiverAdapter extends RecyclerView.Adapter<ReceiverAdapter.ReceiverViewHolder> {
ArrayList<ClientObject> clientList;
Context mContext;
private ReceiverAdapter adapter;
public ReceiverAdapter(Context mContext, ArrayList<ClientObject> clientList) {
this.clientList = clientList;
this.mContext = mContext;
}
#NonNull
#Override
public ReceiverViewHolder onCreateViewHolder(#NonNull ViewGroup parent, int viewType) {
View layoutView = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_callcenter_client, null, false);
RecyclerView.LayoutParams lp = new RecyclerView.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT,ViewGroup.LayoutParams.WRAP_CONTENT);
layoutView.setLayoutParams(lp);
ReceiverViewHolder rcv = new ReceiverViewHolder(layoutView);
return rcv;
}
#Override
public void onBindViewHolder(#NonNull ReceiverViewHolder holder, int position) {
holder.mName.setText(clientList.get(position).getName());
holder.mPhone.setText(clientList.get(position).getPhone());
}
#Override
public int getItemCount() {
return clientList.size();
}
public class ReceiverViewHolder extends RecyclerView.ViewHolder {
public TextView mName, mPhone;
//public LinearLayout mLayout;
public ReceiverViewHolder(#NonNull View itemView) {
super(itemView);
mName = (TextView) itemView.findViewById(R.id.client_name);
mPhone = (TextView) itemView.findViewById(R.id.client_phone);
//mLayout = (LinearLayout) itemView.findViewById(R.id.layoutItemClient);
}
}
}
EDIT
I changed the ReceiverFragment so that it could be more understandable.
That's the FATAL ERROR I get when I use the getContext(). I simply cannot make a connection with my SQLDatabase.
2019-01-31 15:41:45.118 22318-22318/com.example.aliton.passkeybetweenfrags E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.aliton.passkeybetweenfrags, PID: 22318
java.lang.NullPointerException: Attempt to invoke virtual method 'java.io.File android.content.Context.getDatabasePath(java.lang.String)' on a null object reference
at android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked(SQLiteOpenHelper.java:352)
at android.database.sqlite.SQLiteOpenHelper.getReadableDatabase(SQLiteOpenHelper.java:322)
at com.example.aliton.passkeybetweenfrags.ReceiverFragment.clientReading(ReceiverFragment.java:104)
at com.example.aliton.passkeybetweenfrags.ReceiverFragment.getMessageFromSender(ReceiverFragment.java:53)
at com.example.aliton.passkeybetweenfrags.MainActivity.getMessage(MainActivity.java:64)
at com.example.aliton.passkeybetweenfrags.SenderAdapter$1.onCheckedChanged(SenderAdapter.java:54)
at android.widget.CompoundButton.setChecked(CompoundButton.java:171)
at android.widget.CompoundButton.toggle(CompoundButton.java:127)
at android.widget.CompoundButton.performClick(CompoundButton.java:132)
at android.view.View.performClickInternal(View.java:6574)
at android.view.View.access$3100(View.java:778)
at android.view.View$PerformClick.run(View.java:25885)
at android.os.Handler.handleCallback(Handler.java:873)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6669)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
Now, when I suppress getContext() and make it static in mContext. I can make a connection with SQLDatabase, but I get this FATAL error because the ReceiverAdapter:
2019-01-31 15:35:05.541 21936-21936/com.example.aliton.passkeybetweenfrags E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.aliton.passkeybetweenfrags, PID: 21936
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.RecyclerView.setAdapter(android.support.v7.widget.RecyclerView$Adapter)' on a null object reference
at com.example.aliton.passkeybetweenfrags.ReceiverFragment.clientReading(ReceiverFragment.java:110)
at com.example.aliton.passkeybetweenfrags.ReceiverFragment.getMessageFromSender(ReceiverFragment.java:53)
at com.example.aliton.passkeybetweenfrags.MainActivity.getMessage(MainActivity.java:64)
at com.example.aliton.passkeybetweenfrags.SenderAdapter$1.onCheckedChanged(SenderAdapter.java:54)
at android.widget.CompoundButton.setChecked(CompoundButton.java:171)
at android.widget.CompoundButton.toggle(CompoundButton.java:127)
at android.widget.CompoundButton.performClick(CompoundButton.java:132)
at android.view.View.performClickInternal(View.java:6574)
at android.view.View.access$3100(View.java:778)
at android.view.View$PerformClick.run(View.java:25885)
at android.os.Handler.handleCallback(Handler.java:873)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6669)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
I can either get an error while reading the SQLDatabase (client.db) or while updating the ReceiverAdapter.
This is the link for the Main folder of the app:
https://1drv.ms/u/s!AjteqjTsJm9qgn6kODT9OJmMcY4e
This is the link to the SQLDatabase (group.db and client.db)
https://1drv.ms/u/s!AjteqjTsJm9qgn_L52cz3lDWOOWe

I finally found an answer.
The whole problem happened in the MainActivity. I was communicating from the MainActivity to the ReceiverFragment like this :
ReceiverFragment receiverFragment = new ReceiverFragment();
And sending the message like this:
#Override
public void getMessage(String message) {
receiverFragment.getMessageFromSender(message);
}
The message was been passed from MainActivity to ReceiverFragment normally, But I was getting a NullPointerException for the recyclerView of the ReceiverFragment.
The problem was solved by using the following way to deliver the message to the ReceiverFragment (answer found in this link https://www.journaldev.com/14207/android-passing-data-between-fragments):
#Override
public void getMessage(String message) {
String tag = "android:switcher:" + R.id.tabs_pager + ":" + 1;
ReceiverFragment rf = (ReceiverFragment) getSupportFragmentManager().findFragmentByTag(tag);
rf.getMessageFromSender(message);
}
The links for the code and the SQLDatabase (group.db and client.db) are still available for download.
For those who are starting in Android like me and interested in the code, please do not forget to change the delivering function in the MainActivity.
Thank you all and good luck!

Compare Old Data with New Data in Recyclerview

I am new in Android Development and working on a project where I need to call an API after every one second, in that API there is field "Amount"(dBID) which keeps on changing, so I need to update the latest Amount (dBID) in recyclerview.
In order to do so, I have called this API in a service after every interval of one second.
The data is Showing Properly no Issue.
But for Now I need to perform some action on the Old Amount and New Amount.
Action Required : I need to compare the old value (dBID) with the New Value (dBID).
If the New Value is greater then I need to change the Text Color of Amount (dBID) to BLUE.
If the New Value is smaller then I need to change the Text Color of Amount (dBID) to RED.
Tried to achieve this by storing the old data in a Variable and then Comparing it to the new Value.
Issue : This logic is working fine until there are 5 or less Items in recyclerview as soon as the sixth item is added the same logic does not work.
Help me if anyone knows how I can achieve this.
For Example you can refer an App Vertexfx : Quotes Tab.
Below is the Code which I Tried.
Adapter class of the RecyclerView:
public class QuoteAdapter extends RecyclerView.Adapter <QuoteAdapter.MyViewHolder>{
Context context;
List<QuoteData> data;
public QuoteAdapter(Context context,List<QuoteData> data)
{
this.data = data;
this.context = context;
}
class MyViewHolder extends RecyclerView.ViewHolder{
TextView time,symbol,sellmax,selllow,buymax,buylow,buy,sell,spread,lowtext,hightext;
LinearLayout layout,layoutbid,layoutask;
float currentbid,lastbid,currentask,lastask;
public MyViewHolder(#NonNull View itemView) {
super(itemView);
time = itemView.findViewById(R.id.TVTime);
symbol = itemView.findViewById(R.id.TVSymbol);
sellmax = itemView.findViewById(R.id.TVSELLMAX);
selllow = itemView.findViewById(R.id.TVSELLLOW);
buymax = itemView.findViewById(R.id.TVBUYMAX);
buylow = itemView.findViewById(R.id.TVBUYHIGH);
buy = itemView.findViewById(R.id.TVBUY);
sell = itemView.findViewById(R.id.TVSELL);
spread = itemView.findViewById(R.id.TVSpread1);
lowtext = itemView.findViewById(R.id.low);
hightext = itemView.findViewById(R.id.high);
layout = itemView.findViewById(R.id.layout);
layoutbid = itemView.findViewById(R.id.LLBid);
layoutask = itemView.findViewById(R.id.LLAsk);
currentbid = 0;
lastbid = 0;
currentask = 0;
lastask = 0;
}
}
#NonNull
#Override
public MyViewHolder onCreateViewHolder(#NonNull ViewGroup viewGroup, int i) {
View view = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.quotelist,viewGroup,false);
return new MyViewHolder(view);
}
#SuppressLint("ResourceAsColor")
#Override
public void onBindViewHolder(#NonNull final MyViewHolder myViewHolder, final int i) {
final QuoteData data1 = data.get(i);
myViewHolder.time.setText(data1.dLut);
myViewHolder.symbol.setText(data1.dSymbol);
myViewHolder.sellmax.setText(data1.dBid); //Bid
myViewHolder.selllow.setText(data1.dLow);
myViewHolder.buymax.setText(data1.dAsk); //ask
myViewHolder.buylow.setText(data1.dHigh);
myViewHolder.currentbid = Float.parseFloat((data1.dBid));
myViewHolder.currentask = Float.parseFloat((data1.dAsk));
if (myViewHolder.currentbid > myViewHolder.lastbid)
{
myViewHolder.sellmax.setTextColor(Color.BLUE);
}
if (myViewHolder.currentbid < myViewHolder.lastbid)
{
myViewHolder.sellmax.setTextColor(Color.RED);
}
myViewHolder.lastbid = myViewHolder.currentbid;
myViewHolder.lastask = myViewHolder.currentask;
}
});
}

I suggest you take a look at those classes from the Android SDK:
DiffUtil
AsyncListDiffer
ItemAnimator
DiffUtil
DiffUtil is designed to compare existing and new recycler view items and fires appropriate events. You need to pass a callback that can tell if two items are the same and if their content has changed.
AsyncListDiffer
It wraps the DiffUtil and executes it's logic asynchronously, giving better performance.
ItemAnimator
The ItemAnimator for a given RecyclerView is called by default when change events are fired on it's items. You can provide an implementation of the animateChange method to change your color accordingly.

For Future reference I have resolved the above mentioned issue using the below code.
Defined two ArrayList of String in Adapter
public class QuoteAdapter extends RecyclerView.Adapter <QuoteAdapter.MyViewHolder>{
Context context;
List<QuoteData> data;
List<String> olddatabid = new ArrayList<String>();
List<String> newdatabid = new ArrayList<String>();
List<String> olddataask = new ArrayList<String>();
List<String> newdataask = new ArrayList<String>();
class MyViewHolder extends RecyclerView.ViewHolder{
TextView time,symbol,sellmax,selllow,buymax,buylow,buy,sell,spread,lowtext,hightext;
LinearLayout layout,layoutbid,layoutask;
public MyViewHolder(#NonNull View itemView) {
super(itemView);
time = itemView.findViewById(R.id.TVTime);
symbol = itemView.findViewById(R.id.TVSymbol);
sellmax = itemView.findViewById(R.id.TVSELLMAX);
selllow = itemView.findViewById(R.id.TVSELLLOW);
buymax = itemView.findViewById(R.id.TVBUYMAX);
buylow = itemView.findViewById(R.id.TVBUYHIGH);
buy = itemView.findViewById(R.id.TVBUY);
sell = itemView.findViewById(R.id.TVSELL);
spread = itemView.findViewById(R.id.TVSpread1);
lowtext = itemView.findViewById(R.id.low);
hightext = itemView.findViewById(R.id.high);
layout = itemView.findViewById(R.id.layout);
layoutbid = itemView.findViewById(R.id.LLBid);
layoutask = itemView.findViewById(R.id.LLAsk);
}
}
public QuoteAdapter(Context context,List<QuoteData> data)
{
this.data = data;
this.context = context;
}
#NonNull
#Override
public MyViewHolder onCreateViewHolder(#NonNull ViewGroup viewGroup, int i) {
View view = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.quotelist,viewGroup,false);
return new MyViewHolder(view);
}
#SuppressLint("ResourceAsColor")
#Override
public void onBindViewHolder(#NonNull final MyViewHolder myViewHolder, final int i) {
final QuoteData data1 = data.get(i);
myViewHolder.time.setText(data1.dLut);
myViewHolder.symbol.setText(data1.dSymbol);
myViewHolder.sellmax.setText(data1.dBid); //Bid
myViewHolder.selllow.setText(data1.dLow);
myViewHolder.buymax.setText(data1.dAsk); //ask
myViewHolder.buylow.setText(data1.dHigh);
if (newdatabid.size()< data.size())
{
newdatabid.add(data1.dBid); //Insert Value in array for the first time
}
if (olddatabid.size()< data.size())
{
olddatabid.add(data1.dBid); //Insert Value in array for the first time
}
if (newdataask.size()< data.size())
{
newdataask.add(data1.dAsk); //Insert Value in array for the first time
}
if (olddataask.size()< data.size()) //Insert Value in array for the first time
{
olddataask.add(data1.dAsk);
}
newdatabid.set(i,data1.dBid); //Store Value in array
newdataask.set(i,data1.dAsk); //Store Value in array
//Compare and perform Logic
if (Float.valueOf(newdatabid.get(i)) > Float.valueOf(olddatabid.get(i)))
{
myViewHolder.sellmax.setTextColor(Color.BLUE);
}
if (Float.valueOf(newdatabid.get(i)) < Float.valueOf(olddatabid.get(i)))
{
myViewHolder.sellmax.setTextColor(Color.RED);
}
if (Float.valueOf(newdataask.get(i)) > Float.valueOf(olddataask.get(i)))
{
myViewHolder.buymax.setTextColor(Color.BLUE);
}
if (Float.valueOf(newdataask.get(i)) < Float.valueOf(olddataask.get(i)))
{
myViewHolder.buymax.setTextColor(Color.RED);
}
olddatabid.set(i,newdatabid.get(i));
olddataask.set(i,newdataask.get(i));
}
});
}
}
#Override
public int getItemCount() {
return data.size();
}
}

Nested ArrayList while creating RecyclerView

I am developing an android application where i am using a RecyclerView to display a list of items.I am getting the list from server as json.So my problem is within this list i am getting another list as item.That is if my main arraylist contain title and materials, the material is another arraylist.So can you please suggest a solution to display a list within recyclerview.
The code below is my adapter
public class CurriculumAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {
private Context mContext;
private ArrayList<Curriculum> mArrayListCurriculum;
public CurriculumAdapter(Context mContext, ArrayList<Curriculum> mArrayListCurriculum) {
this.mContext = mContext;
this.mArrayListCurriculum = mArrayListCurriculum;
}
#Override
public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View v = LayoutInflater.from(parent.getContext()).inflate(R.layout.adapter_key_features, parent,false);
return new KeyFeatureViewHolder(v);
}
#Override
public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
if (holder instanceof KeyFeatureViewHolder) {
((KeyFeatureViewHolder) holder).mTextViewFeatureTitle.setText(mArrayListCurriculum.get(position).getTitle());
}
}
#Override
public int getItemCount() {
return mArrayListCurriculum == null ? 0 : mArrayListCurriculum.size();
}
public static class KeyFeatureViewHolder extends RecyclerView.ViewHolder {
public TextView mTextViewFeatureTitle;
public KeyFeatureViewHolder(View itemView) {
super(itemView);
mTextViewFeatureTitle = (TextView) itemView.findViewById(R.id.txtFeature);
}
}
}
The code below is my fragment with dummy arraylist data
public class CourseCurriculumFragment extends Fragment {
private FragmentInterface mFragmentInterface;
private ArrayList<Curriculum> mArrayListCurriculum;
private ArrayList<Material> mArrayListMaterial;
private RecyclerView mRecyclerViewCurriculum;
private LinearLayoutManager mLinearLayoutManager;
private CurriculumAdapter mCurriculumAdapter;
#Override
public View onCreateView(LayoutInflater inflater, #Nullable ViewGroup container, #Nullable Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_course_curriculum, container, false);
return view;
}
#Override
public void onViewCreated(View view, #Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
initView(view);
}
private void initView(View view) {
mArrayListMaterial = new ArrayList<>();
mArrayListCurriculum = new ArrayList<>();
populateMaterials();
populateKeyFeatures();
mRecyclerViewCurriculum = (RecyclerView) view.findViewById(R.id.recyclerViewCurriculum);
mCurriculumAdapter = new CurriculumAdapter(getActivity(), mArrayListCurriculum);
mLinearLayoutManager = new LinearLayoutManager(getActivity());
mRecyclerViewCurriculum.setLayoutManager(mLinearLayoutManager);
mRecyclerViewCurriculum.setAdapter(mCurriculumAdapter);
mRecyclerViewCurriculum.setItemAnimator(new DefaultItemAnimator());
}
private void populateMaterials() {
mArrayListMaterial.add(new Material("12:00","pdf","","Sample Text","0"));
mArrayListMaterial.add(new Material("12:00","pdf","","Sample Text","0"));
}
private void populateKeyFeatures() {
mArrayListCurriculum.add(new Curriculum("UNIT 1",mArrayListMaterial));
mArrayListCurriculum.add(new Curriculum("UNIT 2",mArrayListMaterial));
mArrayListCurriculum.add(new Curriculum("UNIT 3",mArrayListMaterial));
}
}

A bind method in a holder is a good way to pass data to it.
In your case this bind method should take in a Curriculum and a Material object as parameters.
Inside the onBindViewHolder method of the adapter, instead of reaching into the variables of the holder, you should call this bind method.
In the implementation of the method inside the you KeyFeatureViewHolder class you should use these passed parameters and display them in the appropriate UI elements.
Lastly, to get the Material object data into adapter, add ArrayList<Material> as a constructor parameter just like you did with Curriculum.

Use RecyclerView with header, title as header and materials as items of that header. Look at this example.

You need to design a custom list for yourself. For example take an object like this.
public class ListItem {
public curriculumName = null;
public materialName = null;
}
Now populate this list after you parse the JSON string. Get your first Curriculum and populate the object like this
private ArrayList<ListItem> mListItemArray = new ArrayList<ListItem> ();
for(curriculum : mArrayListCurriculum) {
ListItem mListItemHead = new ListItem();
mListItemHead.curriculumName = curriculum.getName();
// Set the header here
mListItemArray.add(mListItemHead);
for(material : curriculum.getMaterials()){
ListItem mListItem = new ListItem();
mListItem.materialName = material.getName();
// Add materials here
mListItemArray.add(mListItem);
}
}
Now, you've a list with headers and materials. When the materialName in your mListItemArray is null, it identifies that this is a header and vice versa.
Now the trick is to modify your adapter of your RecyclerView so that you can bind proper view to your items in your list.
You can find an indication from this answer on how you can achieve this desired behaviour.
Basically, the idea is to modify your getItemViewType to pass the proper view in your onBindViewHolder. Your getItemViewType might look like this.
#Override
public int getItemViewType(int position) {
if (mListItemArray.get(position).curriculumName != null) {
// This is where we'll add header.
return HEADER_VIEW;
}
return super.getItemViewType(position);
}