Android Studio "Attempting to call a virtual method by reference to a null object"

Question

when I create a custom view for each item in the list view, I get a null pointer exception and I don’t know why, the layout identifier 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; } } } 

primary occupation:

 <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" /> 

layout view of elements:

 <?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 is a mistake

 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 explanation are welcome

Answer 1

In your code

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

The getLayoutInflater () method cannot be used in the adapter's inner class. Therefore, you should try to create a variable to have an inflatable layout object of the parent class and, therefore, access it, or you can send it in the context of the calling class in the adapter class constructor.

Therefore, 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 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, for example:

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

Answer 2

Try changing the appropriate code inside your adapter class to the following

 @Override public View getView(int position, View convertView, ViewGroup parent) { LayoutInflater inflater = (LayoutInflater)getSystemService(Context.LAYOUT_INFLATER_SERVICE); View itemView; if (convertView == null) { itemView = inflater.inflate(R.layout.item_view, parent, false); } else { itemView = convertView; } ... ... return itemView; }