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Im new in Android Studio and Im working in my college capstone project, and I`m trying to generate some cards trough recyclerview.
The problem is that depending on the CardID, I need to change the card Icon and the header card background color, and for both command the program crash and shows that error " Attempt to invoke virtual method....on a null object reference".
I tried different ways to change the images and the background color but with no success, and following the research that I did here, I believe that both command are correct:

 viewHolder.backgroundHeader.setBackgroundColor(Color.parseColor("#567845"));
 viewHolder.iconCard.setImageResource(R.drawable.health_icon);

This is my XML layout file that I`m using to generate the cards:

 <?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
 xmlns:app="http://schemas.android.com/apk/res-auto"
 xmlns:tools="http://schemas.android.com/tools"
 android:id="@+id/longTermCardHealth"
 android:layout_width="match_parent"
 android:layout_height="wrap_content"
 android:layout_marginTop="0dp"
 android:layout_marginBottom="10dp"
 android:background="@color/monocolorPallete04"
 android:orientation="vertical"
 tools:context=".LongTermCardHealth">

 <android.support.v7.widget.CardView
 android:id="@+id/card_view"
 android:layout_width="match_parent"
 android:layout_height="wrap_content"
 android:elevation="3dp">

<LinearLayout
 android:layout_width="match_parent"
 android:layout_height="wrap_content"
 android:orientation="vertical">


 <GridLayout
 android:id="@+id/backgroundHeader"
 android:layout_width="match_parent"
 android:layout_height="wrap_content"
 android:background="@color/mainPallete02">

 <ImageView
 android:id="@+id/iconCard"
 android:layout_width="43dp"
 android:layout_height="42dp"
 android:layout_marginLeft="20dp"
 android:layout_marginTop="8dp"
 android:layout_weight="1"
 app:srcCompat="@drawable/fun_icon" />

 <LinearLayout
 android:layout_width="wrap_content"
 android:layout_height="wrap_content"
 android:layout_marginLeft="5dp"
 android:layout_marginRight="60dp"
 android:orientation="vertical"
 android:paddingTop="5dp">

 <TextView
 android:id="@+id/categoryLabel"
 android:layout_width="200dp"
 android:layout_height="wrap_content"
 android:text="HEALTH"
 android:textColor="@color/monocolorPallete04"
 android:textSize="18sp" />

 <TextView
 android:id="@+id/cardTitle"
 android:layout_width="match_parent"
 android:layout_height="wrap_content"
 android:text="Get in shape for skiing"
 android:textColor="@color/monocolorPallete04"
 android:textSize="20sp"
 app:fontFamily="@font/alegreya_sans_medium_italic" />

 </LinearLayout>
 </GridLayout>


 <GridLayout
 android:layout_width="match_parent"
 android:layout_height="wrap_content"
 android:layout_marginLeft="20dp"
 android:layout_marginTop="30dp"
 android:layout_marginRight="20dp"
 android:orientation="horizontal">

 <ImageView
 android:id="@+id/imageView4"
 android:layout_width="10dp"
 android:layout_height="20dp"
 android:layout_marginRight="5dp"
 android:layout_weight="1"
 app:srcCompat="@drawable/ic_list_icon" />

 <TextView
 android:id="@+id/goalsCompleted"
 android:layout_width="30dp"
 android:layout_height="wrap_content"
 android:layout_weight="1"
 android:width="50dp"
 android:text="3/4" />

 <TextView
 android:id="@+id/goalsCompletedText"
 android:layout_width="131dp"
 android:layout_height="wrap_content"
 android:layout_weight="1"
 android:width="250dp"
 android:text="COMPLETED" />

 <ImageView
 android:id="@+id/imageView5"
 android:layout_width="10dp"
 android:layout_height="20dp"
 android:layout_gravity="top"
 android:layout_marginRight="5dp"
 android:layout_weight="1"
 app:srcCompat="@drawable/ic_calelndar_icon" />

 <TextView
 android:id="@+id/dateComplete"
 android:layout_width="wrap_content"
 android:layout_height="wrap_content"
 android:layout_weight="1"
 android:text="FEBRUARY 28" />


 </GridLayout>

 <LinearLayout
 android:layout_width="match_parent"
 android:layout_height="wrap_content"
 android:layout_marginLeft="20dp"
 android:layout_marginRight="20dp"
 android:layout_marginBottom="20dp"
 android:orientation="horizontal">

 <ProgressBar
 android:id="@+id/progressBar"
 style="?android:attr/progressBarStyleHorizontal"
 android:layout_width="wrap_content"
 android:layout_height="wrap_content"
 android:layout_weight="1"
 android:progress="75" />
 </LinearLayout>
</LinearLayout>
 </android.support.v7.widget.CardView>

</LinearLayout>

And this is my LongTErm page that calls the RecyclerView to generate the cards:

 package com.example.hackachieve;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.view.View;
import android.content.Intent;
import android.widget.ImageView;

import org.json.JSONException;
import org.json.JSONObject;
import org.json.JSONArray;

import java.util.ArrayList;


public class LongTermPage extends AppCompatActivity

// Creating longTermCardVariable(one variable for each card)
 private ImageView ongoingButton;
 private ImageView addButton;
 private ImageView completedButton;

 //vars
 private ArrayList<String> mCardTitle = new ArrayList<>();
 private ArrayList<String> mGoalsCompleted = new ArrayList<>();
 private ArrayList<String> mDataCompleted = new ArrayList<>();
 private ArrayList<Integer> mBoard_id = new ArrayList<Integer>();

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

 initVars();


// Defining Bottom Buttons
 ongoingButton = (ImageView) findViewById(R.id.ongoingIcon);
 addButton = (ImageView) findViewById(R.id.addIcon);
 completedButton = (ImageView) findViewById(R.id.completedIcon);


 completedButton.setOnClickListener(new View.OnClickListener() 
 @Override
 public void onClick(View v) 
 openLongTermGoalsCompleted();
 
 );

 

 public void openLongTermGoalsCompleted()
 Intent intent = new Intent(this, LongTermPageCompleted.class);
 startActivity(intent);
 overridePendingTransition(R.anim.slide_in_right, R.anim.slide_out_left);
 

 private void initVars()

 mCardTitle.add("Save Money to Buy a Car");
 mGoalsCompleted.add("6");
 mDataCompleted.add("2019-03-14T16:36:25.019Z");
 mBoard_id.add(1);

 mCardTitle.add("Get in shape until winter");
 mGoalsCompleted.add("5");
 mDataCompleted.add("2019-02-14T16:36:25.019Z");
 mBoard_id.add(2);

 mCardTitle.add("Invest money in Bitcoins");
 mGoalsCompleted.add("4");
 mDataCompleted.add("2019-01-14T16:36:25.019Z");
 mBoard_id.add(1);

 mCardTitle.add("Learn Yoga");
 mGoalsCompleted.add("3");
 mDataCompleted.add("2019-04-14T16:36:25.019Z");
 mBoard_id.add(2);

 initRecyclerView();
 

 private void initRecyclerView()
 RecyclerView recyclerView = findViewById(R.id.recycler_view);
 RecyclerViewAdapter adapter = new RecyclerViewAdapter(this, mCardTitle, mGoalsCompleted,mDataCompleted, mBoard_id);
 recyclerView.setAdapter(adapter);
 recyclerView.setLayoutManager(new LinearLayoutManager(this));
 

This is my Recycler view file, and I commented before exactly the part that Im trying t change the background color and the Icon that gives the error, and I tried to execute one isolated or another and didnt work:

package com.example.hackachieve;

import android.annotation.SuppressLint;
import android.graphics.Color;
import android.support.annotation.NonNull;
import android.support.v7.widget.AppCompatImageView;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.GridLayout;
import android.widget.ImageView;
import android.widget.LinearLayout;
import android.widget.TextView;

import java.util.ArrayList;

public class RecyclerViewAdapter extends RecyclerView.Adapter<RecyclerViewAdapter.ViewHolder>

 private static final String TAG = "RecyclerViewAdapter";
 private ArrayList<String> mCardTitle = new ArrayList<>();
 private ArrayList<String> mGoalsCompleted = new ArrayList<>();
 private ArrayList<String> mDataCompleted = new ArrayList<>();
 private ArrayList<Integer> mBoard_id = new ArrayList<Integer>();
// private String iconCard;

 public RecyclerViewAdapter(LongTermPage longTermPage, ArrayList<String> mCardTitle, ArrayList<String> mGoalsCompleted, ArrayList<String> mDataCompleted, ArrayList<Integer> mBoard_id) 
 this.mCardTitle = mCardTitle;
 this.mGoalsCompleted = mGoalsCompleted;
 this.mDataCompleted = mDataCompleted;
 this.mBoard_id = mBoard_id;
 

 @NonNull
 @Override
 public ViewHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int position) 
 View cardType = null;
 if (mBoard_id.get(position) == 1)
 cardType= LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.activity_long_term_card_finance, viewGroup,false);
 
 if (mBoard_id.get(position) == 2)
 cardType = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.activity_long_term_card_health, viewGroup,false);
 
 View view = cardType;
 ViewHolder holder = new ViewHolder(view);
 return holder;
 

 @SuppressLint("ResourceAsColor")
 @Override
 public void onBindViewHolder(@NonNull ViewHolder viewHolder, int position) 
 viewHolder.cardTitle.setText(mCardTitle.get(position));
 viewHolder.goalsCompleted.setText(mGoalsCompleted.get(position));
 viewHolder.dateComplete.setText(mDataCompleted.get(position));

 if(mBoard_id.get(position) == 2) 
 viewHolder.categoryLabel.setText("HEALTH");

// Both command bellow are presenting the same "attempt to invoke virtual method '....' on a null object reference" error
 viewHolder.backgroundHeader.setBackgroundColor(Color.parseColor("#567845"));
 viewHolder.iconCard.setImageResource(R.drawable.health_icon);

 
 if(mBoard_id.get(position) == 1) 
 viewHolder.categoryLabel.setText("FINANCE");
 

 

 @Override
 public int getItemCount() 
 return mCardTitle.size();
 

 public class ViewHolder extends RecyclerView.ViewHolder

 TextView cardTitle;
 TextView goalsCompleted;
 TextView dateComplete;
 ImageView iconCard;
 GridLayout backgroundHeader;
 TextView categoryLabel;

 public ViewHolder(View itemView) 
 super(itemView);
 cardTitle = itemView.findViewById(R.id.cardTitle);
 goalsCompleted = itemView.findViewById(R.id.goalsCompleted);
 dateComplete = itemView.findViewById(R.id.dateComplete);
 iconCard = itemView.findViewById(R.id.iconCard);
 backgroundHeader = itemView.findViewById(R.id.backgroundHeader);
 categoryLabel = itemView.findViewById(R.id.categoryLabel);
 
 

To finalize, this is the full error that shows when I try to execute my program:

E/AndroidRuntime: FATAL EXCEPTION: main
 Process: com.example.hackachieve, PID: 12375
 java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ImageView.setImageResource(int)' on a null object reference
 at com.example.hackachieve.RecyclerViewAdapter.onBindViewHolder(RecyclerViewAdapter.java:59)
 at com.example.hackachieve.RecyclerViewAdapter.onBindViewHolder(RecyclerViewAdapter.java:18)
 at android.support.v7.widget.RecyclerView$Adapter.onBindViewHolder(RecyclerView.java:6781)
 at android.support.v7.widget.RecyclerView$Adapter.bindViewHolder(RecyclerView.java:6823)
 at android.support.v7.widget.RecyclerView$Recycler.tryBindViewHolderByDeadline(RecyclerView.java:5752)
 at android.support.v7.widget.RecyclerView$Recycler.tryGetViewHolderForPositionByDeadline(RecyclerView.java:6019)
 at android.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:5858)
 at android.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:5854)
 at android.support.v7.widget.LinearLayoutManager$LayoutState.next(LinearLayoutManager.java:2230)
 at android.support.v7.widget.LinearLayoutManager.layoutChunk(LinearLayoutManager.java:1557)
 at android.support.v7.widget.LinearLayoutManager.fill(LinearLayoutManager.java:1517)
 at android.support.v7.widget.LinearLayoutManager.onLayoutChildren(LinearLayoutManager.java:612)
 at android.support.v7.widget.RecyclerView.dispatchLayoutStep2(RecyclerView.java:3924)
 at android.support.v7.widget.RecyclerView.dispatchLayout(RecyclerView.java:3641)
 at android.support.v7.widget.RecyclerView.onLayout(RecyclerView.java:4194)
 at android.view.View.layout(View.java:22399)
 at android.view.ViewGroup.layout(ViewGroup.java:6572)
 at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1812)
 at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1656)
 at android.widget.LinearLayout.onLayout(LinearLayout.java:1565)
 at android.view.View.layout(View.java:22399)
 at android.view.ViewGroup.layout(ViewGroup.java:6572)
 at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
 at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
 at android.view.View.layout(View.java:22399)
 at android.view.ViewGroup.layout(ViewGroup.java:6572)
 at android.support.v7.widget.ActionBarOverlayLayout.onLayout(ActionBarOverlayLayout.java:444)
 at android.view.View.layout(View.java:22399)
 at android.view.ViewGroup.layout(ViewGroup.java:6572)
 at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
 at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
 at android.view.View.layout(View.java:22399)
 at android.view.ViewGroup.layout(ViewGroup.java:6572)
 at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1812)
 at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1656)
 at android.widget.LinearLayout.onLayout(LinearLayout.java:1565)
 at android.view.View.layout(View.java:22399)
 at android.view.ViewGroup.layout(ViewGroup.java:6572)
 at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
 at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
 at com.android.internal.policy.DecorView.onLayout(DecorView.java:1042)
 at android.view.View.layout(View.java:22399)
 at android.view.ViewGroup.layout(ViewGroup.java:6572)
 at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:3340)
 at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2804)
 at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1850)
 at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:8455)
 at android.view.Choreographer$CallbackRecord.run(Choreographer.java:949)
 at android.view.Choreographer.doCallbacks(Choreographer.java:761)
 at android.view.Choreographer.doFrame(Choreographer.java:696)
 at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:935)
 at android.os.Handler.handleCallback(Handler.java:873)
 at android.os.Handler.dispatchMessage(Handler.java:99)
 at android.os.Looper.loop(Looper.java:214)
E/AndroidRuntime: at android.app.ActivityThread.main(ActivityThread.java:6981)
 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:1445)
I/Process: Sending signal. PID: 12375 SIG: 9
Application terminated.

If someone has some idea about what can be the solution to solve it, I really appreciate.

Thank you