Android Studio "Versuch, virtuelle Methode auf eine Null-Objekt Referenz aufzurufen"

Question

Wenn ich die benutzerdefinierte Ansicht jedes Elements der Listenansicht erstellen, bekomme ich eine Nullzeiger Ausnahme und ich weiß nicht, warum die Layout-ID scheint

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; 
    } 
} 
} 

Haupttätigkeit 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" /> 

der Artikel Ansicht 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" /> 

und hier der Fehler

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) 

jede Hilfe und explanition begrüßt

Answer 1

In Ihr Code

Die getLayoutInFlater() -Methode kann nicht in der inneren Adapterklasse verwendet werden. Daher sollten Sie versuchen, eine Variable zu erstellen, um das Layout-Inflater-Objekt der Elternklasse zu erhalten und damit darauf zuzugreifen, oder Sie können den Kontext der aufrufenden Klasse im Konstruktor der Adapterklasse senden.

Daher können Sie entweder wie folgt verwenden:

public class ActivityMainWish extends Activity { 

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

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

und verwenden diese inflater Variable hier: itemView = inflater.inflate (R.layout.item_view, Eltern, false);

Oder wie folgt aus:

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); 

und das Kontextobjekt senden wie:

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

Answer 2

Versuchen Sie, den entsprechenden Code in Ihrem Adapter Klasse Wechsel in den folgenden

@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; 
}