firebase nullpointerexception android-recyclerview android-tabbed-activity

Android-Firebase- java.lang.NullPointerException in recyclerView

I am making a tabbed activity with multiple fragments which populate themselves with RecyclerView and the data for this is being retrieved from Firebase Realtime database and Storage as backend.

The error:

E/AndroidRuntime: FATAL EXCEPTION: main
              Process: com.example.visan.peds, PID: 1522
              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.visan.peds.Landing_mother.getData(Landing_mother.java:76)
                  at com.example.visan.peds.Landing_mother.onCreateView(Landing_mother.java:43)
                  at android.support.v4.app.Fragment.performCreateView(Fragment.java:2087)
                  at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1113)
                  at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1295)
                  at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:801)
                  at android.support.v4.app.FragmentManagerImpl.execSingleAction(FragmentManager.java:1643)
                  at android.support.v4.app.BackStackRecord.commitNowAllowingStateLoss(BackStackRecord.java:679)
                  at android.support.v4.app.FragmentPagerAdapter.finishUpdate(FragmentPagerAdapter.java:143)
                  at android.support.v4.view.ViewPager.populate(ViewPager.java:1272)
                  at android.support.v4.view.ViewPager.populate(ViewPager.java:1120)
                  at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1646)
                  at android.view.View.measure(View.java:18991)
                  at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:716)
                  at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:462)
                  at android.view.View.measure(View.java:18991)
                  at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5952)
                  at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
                  at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:139)
                  at android.view.View.measure(View.java:18991)
                  at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5952)
                  at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1465)
                  at android.widget.LinearLayout.measureVertical(LinearLayout.java:748)
                  at android.widget.LinearLayout.onMeasure(LinearLayout.java:630)
                  at android.view.View.measure(View.java:18991)
                  at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5952)
                  at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
                  at android.view.View.measure(View.java:18991)
                  at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5952)
                  at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1465)
                  at android.widget.LinearLayout.measureVertical(LinearLayout.java:748)
                  at android.widget.LinearLayout.onMeasure(LinearLayout.java:630)
                  at android.view.View.measure(View.java:18991)
                  at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5952)
                  at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
                  at com.android.internal.policy.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2645)
                  at android.view.View.measure(View.java:18991)
                  at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2403)
                  at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1342)
                  at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1591)
                  at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1233)
                  at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6552)
                  at android.view.Choreographer$CallbackRecord.run(Choreographer.java:919)
                  at android.view.Choreographer.doCallbacks(Choreographer.java:710)
                  at android.view.Choreographer.doFrame(Choreographer.java:645)
                  at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:905)
                  at android.os.Handler.handleCallback(Handler.java:739)
                  at android.os.Handler.dispatchMessage(Handler.java:95)
                  at android.os.Looper.loop(Looper.java:148)
                  at android.app.ActivityThread.main(ActivityThread.java:5582)
                  at java.lang.reflect.Method.invoke(Native Method)
                  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
                  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

My Main Activity, Landing.java

package com.example.visan.peds;

import android.os.Bundle;
import android.support.design.widget.TabLayout;
import android.support.v4.view.ViewPager;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;

public class Landing extends AppCompatActivity {

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

    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    TabLayout tabLayout=(TabLayout)findViewById(R.id.tab_layout);
    tabLayout.addTab(tabLayout.newTab().setText("CHILD"));
    tabLayout.addTab(tabLayout.newTab().setText("MOTHER"));
    tabLayout.setTabGravity(TabLayout.GRAVITY_FILL);

    final ViewPager viewPager=(ViewPager) findViewById(R.id.pager);
    final Landing_frag_manager frag_manager=new Landing_frag_manager(getSupportFragmentManager(),tabLayout.getTabCount(),Landing.this);

    viewPager.setAdapter(frag_manager);
    viewPager.addOnPageChangeListener(new TabLayout.TabLayoutOnPageChangeListener(tabLayout));

    tabLayout.setOnTabSelectedListener(new TabLayout.OnTabSelectedListener(){
        @Override
        public void onTabReselected(TabLayout.Tab tab) {
            viewPager.setCurrentItem(tab.getPosition());
        }

        @Override
        public void onTabSelected(TabLayout.Tab tab) {

        }

        @Override
        public void onTabUnselected(TabLayout.Tab tab) {

        }
    });
}

}

Its layout file, activity_landing.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
android:id="@+id/main_layout"
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:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">

<android.support.v7.widget.Toolbar
    android:id="@+id/toolbar"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_alignParentTop="true"
    android:background="?attr/colorPrimary"
    android:elevation="6dp"
    android:minHeight="?attr/actionBarSize"
    android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
    app:popupTheme="@style/ThemeOverlay.AppCompat.Light"/>

<android.support.design.widget.TabLayout
    android:id="@+id/tab_layout"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_below="@+id/toolbar"
    android:background="?attr/colorPrimary"
    android:elevation="6dp"
    android:minHeight="?attr/actionBarSize"
    android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"/>

<android.support.v4.view.ViewPager
    android:id="@+id/pager"
    android:layout_width="match_parent"
    android:layout_height="fill_parent"
    android:layout_below="@id/tab_layout"/>

</RelativeLayout>

The fragment adapter, Landing_frag_manager.java

    package com.example.visan.peds;

import android.content.Context;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;

public class Landing_frag_manager extends FragmentPagerAdapter {
    private int num_of_tabs;
    Context context;

    public Landing_frag_manager(FragmentManager fm, int numOfTabs, Context context){
        super(fm);
        this.num_of_tabs=numOfTabs;
        this.context=context;
    }

    @Override
    public Fragment getItem(int position) {
        switch (position){
            case 0:
                Landing_child child=new Landing_child();
                return child;
            case 1:
                Landing_mother mother=new Landing_mother();
                return mother;
            default:
                return null;
        }
    }

    @Override
    public int getCount() {
        return num_of_tabs;
    }
}

Code for Fragment, Landing_mother.java

package com.example.visan.peds;

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.google.firebase.database.ValueEventListener;

import java.util.ArrayList;
import java.util.List;


public class Landing_mother extends Fragment {

    private List<Ailment> ailments;

    private RecyclerView recyclerView;
    LinearLayoutManager layoutManager;
    private RecyclerView.Adapter adapter;

    public Landing_mother(){}

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

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

        ailments=new ArrayList<>();
        getData();

        recyclerView =(RecyclerView)view.findViewById(R.id.recyclerView1);
        recyclerView.setHasFixedSize(true);

        layoutManager=new LinearLayoutManager(getActivity());
        layoutManager.setOrientation(LinearLayoutManager.VERTICAL);
        recyclerView.setLayoutManager(layoutManager);
        return view;
    }

    private void getData(){
        FirebaseDatabase db=FirebaseDatabase.getInstance();
        DatabaseReference ref=db.getReference().child("Mother").child("0");

        ref.addListenerForSingleValueEvent(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                if (dataSnapshot.exists()){
                    Log.v("SNAPSHOT::",dataSnapshot.toString());
                    for (DataSnapshot snapshot:dataSnapshot.getChildren()){
                        Ailment ailment=snapshot.getValue(Ailment.class);
                        ailments.add(ailment);
                    }
                }
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });
        adapter=new LandingAdapter(ailments,getActivity());
        recyclerView.setAdapter(adapter);
    }
}

Its layout file, fragment_landing_mother.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
    android:orientation="vertical"
    android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity">

    <android.support.v7.widget.RecyclerView
        android:id="@+id/recyclerView1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">
    </android.support.v7.widget.RecyclerView>


</LinearLayout>

The Ailment object class, Ailment.java

package com.example.visan.peds;

public class Ailment {
    private String name, image_url;

    public void setName(String name){
        this.name=name;
    }
    public String getName(){
        return name;
    }

    public void setImage_url(String image_url){
        this.image_url=image_url;
    }

    public String getImage_url(){
        return image_url;
    }
}

Adapterfor RecyclerView, LandingAdapter.java

package com.example.visan.peds;

import android.content.Context;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.TextView;

import com.bumptech.glide.Glide;
import com.firebase.ui.storage.images.FirebaseImageLoader;
import com.google.firebase.storage.FirebaseStorage;
import com.google.firebase.storage.StorageReference;

import java.util.List;

public class LandingAdapter extends RecyclerView.Adapter<LandingAdapter.ViewHolder>{

    private List<Ailment> list;
    private Context context;
    FirebaseStorage storage;
    LayoutInflater inflater;

    public LandingAdapter(List<Ailment> list, Context context){
        super();
        this.list=list;
        this.context=context;
        inflater=LayoutInflater.from(context);
    }

    @Override
    public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View itemView = LayoutInflater.from(parent.getContext()).inflate(R.layout.landing_list_row,parent,false);
        ViewHolder viewHolder=new ViewHolder(itemView);
        return viewHolder;
    }

    @Override
    public void onBindViewHolder(ViewHolder holder, int position) {
        Ailment ailment=list.get(position);

        StorageReference storageReference=storage.getReferenceFromUrl(ailment.getImage_url());
        Glide.with(context).using(new FirebaseImageLoader()).load(storageReference).into(holder.imageView);

        holder.textView.setText(ailment.getName());
    }

    @Override
    public int getItemCount() {
        return list.size();
    }

    class ViewHolder extends RecyclerView.ViewHolder{
        public ImageView imageView;
        public TextView textView;

        public ViewHolder(View view){
            super(view);
            imageView=(ImageView)view.findViewById(R.id.row_image);
            textView=(TextView)view.findViewById(R.id.row_name);
        }
    }
}

Layout file for Single Row of recyclerView, landing_list_row.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent">
    <ImageView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/row_image"/>
    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/row_name"
        android:layout_below="@+id/row_image"/>

</RelativeLayout>

Solution

Your are calling getData(); which is trying to access RecyclerView before it has been initialised. Call it after you finish recycler view initialisation. For example after recyclerView.setLayoutManager(layoutManager);