Android的工作室＆QUOT;尝试在空对象引用＆QUOT调用虚函数; [英] Android studio " Attempt to invoke virtual method on a null object reference"

问题描述

当我创建的列表视图中的每个项目的自定义视图，我得到一个空指针异常，我不知道为什么，布局ID似乎是正确的。

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;
    }
}
}

主要活动布局：

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" />

该项目视图布局：

<?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" />

和这里的错误

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)

任何帮助和explanition受到欢迎。

any help and explanition is welcomed

推荐答案

在你的code

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

的getLayoutInflater（）方法，没有在内部适配器类可用。因此，你应该尝试创建一个变量有父类的布局充气物体，因此访问它，或者你可以把在调用类的上下文中的适配器类的构造函数。

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.

因此​​，你可以使用这样的：

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()
...
}

和使用充气变量在这里：     ItemView控件= inflater.inflate（R.layout.item_view，父母，假）;

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

或者是这样的：

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);

和发送上下文对象，如：

and send the Context object like:

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

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