Android studio " Attempt to invoke virtual method on a null object reference"

Question

when i create the custom view of each items of the list view, i get a null pointer exception and i dont know why, the layout id seems correct

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.TextView;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;


public class ActivityMainWish extends Activity {

private List<Wish> myWishs = new ArrayList<>();

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

    creerListe();
    creerListeView();
    afficherWishView();
    ajouterWishListe();
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.menu_activity_main_wish, 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.action_settings) {
        //fct
        return true;
    }
    if (id ==R.id.action_add_wish){
        startActivity(new Intent(this,ActivityAddWish.class));
        return true;
    }
    return super.onOptionsItemSelected(item);
}

public void creerListe() {
    myWishs.add(new Wish("Voiture", 50000, getResources().getDrawable(R.drawable.voiture,null)));
    myWishs.add(new Wish("TV", 5000, getResources().getDrawable(R.drawable.tv,null)));
    myWishs.add(new Wish("Smartphone", 500, getResources().getDrawable(R.drawable.smarphone, null)));
}

public void creerListeView (){
    //convertire les items en views appropier
    //prend cette liste, le Layout utilise (creer), et la liste d'items a afficher
    ArrayAdapter<Wish> adapter = new MyListAdapter();
    //prend la liste
    ListView list = (ListView) findViewById(R.id.ListViewWishList);
    //configure la liste
    list.setAdapter(adapter);
}

private class MyListAdapter extends ArrayAdapter<Wish>{
    public MyListAdapter(){
        super(ActivityMainWish.this, R.layout.item_view, myWishs);
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        View itemView = convertView;
        if (itemView==null)
            itemView = getLayoutInflater().inflate(R.layout.item_view, parent, false);

        Wish currentWish = myWishs.get(position);

        TextView textView = (TextView) itemView.findViewById(R.id.TextViewWishListNom);
        textView.setText((currentWish.getNom()));

        TextView prixView = (TextView) itemView.findViewById(R.id.TextViewWishListPrix);
        prixView.setText(("" + currentWish.getPrix()));

        ImageView imageView = (ImageView) itemView.findViewById(R.id.ImageViewWishListImage);
        imageView.setImageDrawable(currentWish.getImage());

        return itemView;
    }
}
}

main activity layout :

<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
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=".ActivityMainWish">

<ListView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/ListViewWishList"
    android:layout_alignParentTop="true"
    android:layout_centerHorizontal="true" />

the item view layout :

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="@+id/wishList">

<ImageView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/ImageViewWishListImage"
    android:src="@drawable/voiture"
    android:minWidth="80dp"
    android:minHeight="80dp"
    android:layout_alignParentLeft="true"
    android:layout_alignParentTop="true"
    android:adjustViewBounds="true"
    android:maxHeight="80dp"
    android:maxWidth="80dp" />

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:textAppearance="?android:attr/textAppearanceLarge"
    android:text="Voiture"
    android:id="@+id/TextViewWishListNom"
    android:layout_alignParentTop="true"
    android:layout_alignParentEnd="true" />

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:textAppearance="?android:attr/textAppearanceSmall"
    android:text="50000"
    android:id="@+id/TextViewWishListPrix"
    android:layout_alignBottom="@+id/ImageViewWishListImage"
    android:layout_alignParentEnd="true" />

and here the error

java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.View.findViewById(int)' on a null object reference
        at com.gokhan.mywishlist.ActivityMainWish$MyListAdapter.getView(ActivityMainWish.java:90)
        at android.widget.AbsListView.obtainView(AbsListView.java:2347)
        at android.widget.ListView.measureHeightOfChildren(ListView.java:1270)
        at android.widget.ListView.onMeasure(ListView.java:1182)
        at android.view.View.measure(View.java:17547)
        at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:727)
        at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:463)
        at android.view.View.measure(View.java:17547)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5535)
        at android.widget.FrameLayout.onMeasure(FrameLayout.java:436)
        at android.view.View.measure(View.java:17547)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5535)
        at com.android.internal.widget.ActionBarOverlayLayout.onMeasure(ActionBarOverlayLayout.java:447)
        at android.view.View.measure(View.java:17547)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5535)
        at android.widget.FrameLayout.onMeasure(FrameLayout.java:436)
        at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2615)
        at android.view.View.measure(View.java:17547)
        at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2015)
        at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1173)
        at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1379)
        at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1061)
        at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5885)
        at android.view.Choreographer$CallbackRecord.run(Choreographer.java:767)
        at android.view.Choreographer.doCallbacks(Choreographer.java:580)
        at android.view.Choreographer.doFrame(Choreographer.java:550)
        at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:753)
        at android.os.Handler.handleCallback(Handler.java:739)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:135)
        at android.app.ActivityThread.main(ActivityThread.java:5254)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)

any help and explanition is welcomed

Answer 1

In your code

itemView = getLayoutInflater().inflate(R.layout.item_view, parent, false);

the getLayoutInflater() method is not usable in The inner adapter class. Hence you should try creating an Variable to have the Layout inflater object of the parent class and hence access it ,or you can send in the context of the calling class in the constructor of the adapter class.

Hence you can use either like this:

public class ActivityMainWish extends Activity {

LayoutInflate inflater;
private List<Wish> myWishs = new ArrayList<>();

@Override
protected void onCreate(Bundle savedInstanceState) {
inflater=getLayoutInflater()
...
}

and use this inflater variable over here: itemView = inflater.inflate(R.layout.item_view, parent, false);

Or like this:

private class MyListAdapter extends ArrayAdapter<Wish>{
private Context mContext;
public MyListAdapter(Context ctx){
    super(ActivityMainWish.this, R.layout.item_view, myWishs);
    mContext=ctx;
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    View itemView = convertView;
    if (itemView==null)
        itemView = LayoutInflater.from(mContext).inflate(R.layout.item_view, parent, false);

and send the Context object like:

ArrayAdapter<Wish> adapter = new MyListAdapter(getApplicationContext());