错误：尝试调用虚方法＆＃39; void android.widget.ListView.setAdapter

Question

我正在使用改造从服务器获取JSON，现在我想使用listView来显示它，但显然我卡住了。我对android比较新，所以我可能会做的完全错了。 我试图创建一个ListView并将POJO对象提供给适配器，但适配器似乎崩溃导致零点异常。任何帮助将不胜感激

清单：

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<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.nmc.viewbeem">
    <uses-permission android:name="android.permission.INTERNET"/>

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity
            android:name=".MainActivity"
            android:label="@string/app_name"
            android:theme="@style/AppTheme.NoActionBar">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

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主要活动：

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package com.nmc.viewbeem;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;

import android.widget.ListAdapter;
import android.widget.ListView;


import retrofit2.Call;
import retrofit2.Callback;
import retrofit2.Response;
import retrofit2.Retrofit;
import retrofit2.converter.gson.GsonConverterFactory;


public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);


        Retrofit retrofit = new Retrofit.Builder()
                .baseUrl("http://nmc.no-ip.org:8888/")
                .addConverterFactory(GsonConverterFactory.create())
                .build();


        StreamingOfferService service = retrofit.create(StreamingOfferService.class);
        Call<ResponseResult> response = service.getStreamingOffers();


        response.enqueue(new Callback<ResponseResult>() {
            @Override
            public void onResponse(Call<ResponseResult> result, Response<ResponseResult> response) {
                ListView listview = (ListView) findViewById(R.id.listview);
                StreamingOffersAdapter<ListAdapter> adapter = new StreamingOffersAdapter(this,R.layout.listofusers,response);
                listview.setAdapter(adapter);


            }

            @Override
            public void onFailure(Call<ResponseResult> result, Throwable t) {

            }


        });

    }


    @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_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        int id = item.getItemId();


        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }
}

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适配器：

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package com.nmc.viewbeem;

import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.TextView;

import java.util.List;

import retrofit2.Response;

/**
 * Created by Katerina on 07.04.2016.
 */
public class StreamingAdapter extends BaseAdapter {

      private Context context;
      private int resource;
      private LayoutInflater inflater;
      private List<StreamingOffer> streamingOfferList;


    public StreamingAdapter(Context context, int resource, Response<ResponseResult> response) {

        this.context=context;
        this.resource=resource;
        this.inflater=LayoutInflater.from(context);

        streamingOfferList = response.body().getData();
        

    }


    public class Holder extends User {

        private TextView full_name;
        private TextView location;
        private TextView price;
        private TextView currency_symbol;
        private TextView total_streamed;

        private ImageView background;
        private  ImageView offer;
        private  ImageView profile;
        private  ImageView iconUser;
        private  ImageView iconStar;
    }



    @Override
    public View getView(int position, View convertView, ViewGroup parent) {

        Holder holder = new Holder();
        View itemView = convertView;

        StreamingOffer streamingOffer = getItem(position);
        User u = streamingOffer.getUser();

        if(itemView==null) {
            itemView = inflater.inflate(resource, parent, false);
            itemView.setTag(holder);

            holder.full_name = (TextView) itemView.findViewById(R.id.full_name);
            holder.full_name.setText(u.getFullName());

            holder.location = (TextView) itemView.findViewById(R.id.location);
            holder.location.setText(streamingOffer.getLocation());
            holder.price = (TextView) itemView.findViewById(R.id.price);
            holder.price.setText(streamingOffer.getPrice());

            holder.currency_symbol = (TextView) itemView.findViewById(R.id.currency_symbol);
            holder.currency_symbol.setText(streamingOffer.getCurrencySymbol());
            holder.total_streamed = (TextView) itemView.findViewById(R.id.total_streamed);
            holder.total_streamed.setText(u.getTotalStreamed());


        }
        return itemView;
    }


    @Override
    public int getCount() {
        return streamingOfferList.size();
    }

    @Override
    public StreamingOffer getItem(int position) {
        return streamingOfferList.get(position);
    }

    @Override
    public long getItemId(int position) {
        return 0;
    }



}

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服务

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package com.nmc.viewbeem;
        import android.provider.SyncStateContract;
        import java.util.List;

        import retrofit2.Call;
        import retrofit2.http.Path;
        import retrofit2.http.Query;
        import retrofit2.http.GET;
        import retrofit2.http.Headers;

/**
 * Created by Katerina on 30.03.2016.
 */
public interface StreamingOfferService {

    @Headers("api-key: ukGspo1hmXGp1BkxzAMRYWcOsmpvacHlxPKKkmZX")

    @GET("api/v1/offers")
    Call<ResponseResult> getStreamingOffers();


}

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和logCat：

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04-06 16:27:13.899 3518-3518/? E/Zygote: MountEmulatedStorage()
04-06 16:27:13.899 3518-3518/? E/Zygote: v2
04-06 16:27:13.899 3518-3518/? I/libpersona: KNOX_SDCARD checking this for 10272
04-06 16:27:13.899 3518-3518/? I/libpersona: KNOX_SDCARD not a persona
04-06 16:27:13.939 3518-3518/? I/SELinux: Function: selinux_compare_spd_ram, SPD-policy is existed. and_ver=SEPF_SM-G900F_5.0 ver=27
04-06 16:27:13.939 3518-3518/? I/SELinux: Function: selinux_compare_spd_ram , priority [2] , priority version is VE=SEPF_SM-G900F_5.0-1_0032
04-06 16:27:13.939 3518-3518/? E/SELinux: [DEBUG] get_category: variable seinfo: default sensitivity: NULL, cateogry: NULL
04-06 16:27:13.939 3518-3518/? I/art: Late-enabling -Xcheck:jni
04-06 16:27:13.999 3518-3518/? D/TimaKeyStoreProvider: TimaSignature is unavailable
04-06 16:27:14.009 3518-3518/? D/ActivityThread: Added TimaKeyStore provider
04-06 16:27:14.109 3518-3518/com.nmc.viewbeem D/ResourcesManager: creating new AssetManager and set to /data/app/com.nmc.viewbeem-1/base.apk
04-06 16:27:14.379 3518-3518/com.nmc.viewbeem D/Activity: performCreate Call secproduct feature valuefalse
04-06 16:27:14.379 3518-3518/com.nmc.viewbeem D/Activity: performCreate Call debug elastic valuetrue
04-06 16:27:14.399 3518-3588/com.nmc.viewbeem D/OpenGLRenderer: Render dirty regions requested: true
04-06 16:27:14.429 3518-3588/com.nmc.viewbeem I/Adreno-EGL: <qeglDrvAPI_eglInitialize:410>: EGL 1.4 QUALCOMM build:  ()
                                                            OpenGL ES Shader Compiler Version: E031.25.01.03
                                                            Build Date: 03/03/15 Tue
                                                            Local Branch: LA.BF.1.1_RB1_20150108_025_1077123_1158499
                                                            Remote Branch: 
                                                            Local Patches: 
                                                            Reconstruct Branch: 
04-06 16:27:14.429 3518-3588/com.nmc.viewbeem I/OpenGLRenderer: Initialized EGL, version 1.4
04-06 16:27:14.499 3518-3588/com.nmc.viewbeem I/OpenGLRenderer: HWUI protection enabled for context ,  &this =0xaf922088 ,&mEglDisplay = 1 , &mEglConfig = 8 
04-06 16:27:14.499 3518-3588/com.nmc.viewbeem D/OpenGLRenderer: Enabling debug mode 0
04-06 16:27:14.589 3518-3518/com.nmc.viewbeem I/Timeline: Timeline: Activity_idle id: android.os.BinderProxy@1ddb875a time:316868548
04-06 16:27:14.909 3518-3518/com.nmc.viewbeem D/AndroidRuntime: Shutting down VM
04-06 16:27:14.909 3518-3518/com.nmc.viewbeem E/AndroidRuntime: FATAL EXCEPTION: main
                                                                Process: com.nmc.viewbeem, PID: 3518
                                                                java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference
                                                                    at com.nmc.viewbeem.MainActivity$1.onResponse(MainActivity.java:45)
                                                                    at retrofit2.ExecutorCallAdapterFactory$ExecutorCallbackCall$1$1.run(ExecutorCallAdapterFactory.java:68)
                                                                    at android.os.Handler.handleCallback(Handler.java:739)
                                                                    at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                    at android.os.Looper.loop(Looper.java:145)
                                                                    at android.app.ActivityThread.main(ActivityThread.java:5832)
                                                                    at java.lang.reflect.Method.invoke(Native Method)
                                                                    at java.lang.reflect.Method.invoke(Method.java:372)
                                                                    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1399)
                                                                    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194)

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布局：

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

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="RECENT STREAMING OFFERS"
        android:gravity="center"
        android:textStyle="bold"
        />

<RelativeLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    >
    <ImageView
        android:layout_width="100dp"
        android:layout_height="100dp"
        android:id="@+id/offer"
        android:layout_alignParentStart="true" />

    <ImageView
        android:layout_width="50dp"
        android:layout_height="50dp"
        android:id="@+id/profile"
        android:layout_alignParentTop="true"
        android:layout_toEndOf="@+id/offer" />


    <ImageView
        android:layout_width="10dp"
        android:layout_height="10dp"
        android:id="@+id/iconUser"
        android:layout_toRightOf="@+id/offer"/>


        <ImageView
            android:layout_height="50dp"
            android:layout_width="200dp"
            android:id="@+id/iconStar"
            android:layout_below="@+id/offer"
            android:layout_alignEnd="@+id/location" />


<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/full_name"
    android:layout_toRightOf="@+id/profile"
    android:text="Name Surname"/>
    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/offered"
        android:text="Offered location to stream:"
        android:layout_alignBottom="@+id/profile"
        android:layout_toEndOf="@+id/profile" />
    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/location"
        android:text="Location"
        android:layout_below="@+id/profile"
        android:layout_toEndOf="@+id/profile" />

     <TextView
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
         android:id="@+id/price"
         android:text="10.00"
         android:layout_alignParentTop="true"
         android:layout_toEndOf="@+id/stream" />
    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/currency_symbol"
        android:text="$"
        android:layout_alignParentTop="true"
        android:layout_toEndOf="@+id/price" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/stream"
        android:text="Stream time:"
        android:layout_alignTop="@+id/iconStar"
        android:layout_alignEnd="@+id/offered" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/total_streamed"
        android:text="15 min:"
        android:layout_alignTop="@+id/stream"
        android:layout_alignParentEnd="true"
        android:layout_alignBottom="@+id/stream"
        android:layout_toEndOf="@+id/stream" />

</RelativeLayout>
</LinearLayout>

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的ListView：

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<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <ListView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/listview">
    </ListView>
</FrameLayout>

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activity_main：

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<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/toolbar"
    android:layout_width="match_parent"
    android:layout_height="100dp"
    android:minHeight="100dp">
    tools:context="com.nmc.viewbeem.MainActivity">

    

</RelativeLayout>

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Answer 1

  

发布R.layout.activity_main代码也是.....
  我怀疑你提供的listview ID不正确

您必须在ListView中提供activity_main 使用以下代码替换activity_main.xml：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/toolbar"
    android:layout_width="match_parent"
    android:layout_height="100dp"
    android:minHeight="100dp"
    tools:context="com.nmc.viewbeem.MainActivity">

    <ListView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/listview">
    </ListView>

</RelativeLayout>

修改您的List Adapter，如下所示：

package com.nmc.viewbeem;

import android.app.Activity;
import android.content.Context;
import android.database.DataSetObserver;
import android.support.v7.view.menu.MenuView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.ListAdapter;
import android.widget.TextView;
import  com.nmc.viewbeem.StreamingOffers;

import retrofit2.Callback;
import retrofit2.Response;

/**
 * Created by Katerina on 05.04.2016.
 */
public class StreamingOffersAdapter<L> extends User implements ListAdapter {


    private Activity activity;
    private Context context;
    private Callback<ResponseResult> callback;
    private Response<ResponseResult> response;
    private LayoutInflater inflater;


    public StreamingOffersAdapter(Activity activity) {
        this.activity=activity;
    }

    public StreamingOffersAdapter(Context context,Callback<ResponseResult> callback, Response<ResponseResult> response) {
    this.callback=callback;
    this.response=response;
    this.context=context;
    inflater=(LayoutInflater)context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    }


    public class Holder {

        private TextView full_name;
        private TextView offeredStreams;
        private TextView location;
        private TextView price;
        private TextView currency_symbol;
        private TextView total_streamed;

        private  ImageView background;
        private  ImageView offer;
        private  ImageView profile;
        private  ImageView iconUser;
        private  ImageView icoStar;
    }
    @Override
    public View getView(int position, View convertView, ViewGroup parent) {

        Holder holder = new Holder();
        View itemView = convertView;
        itemView = inflater.inflate(R.layout.listofusers, null);
        StreamingOffers s = new StreamingOffers();
        User u = new User();

       if(itemView==null) {

           holder.full_name = (TextView) itemView.findViewById(R.id.full_name);
           holder.full_name.setText(getFullName());

           holder.location = (TextView) itemView.findViewById(R.id.location);
           holder.location.setText(s.getLocation());
           holder.price = (TextView) itemView.findViewById(R.id.price);
           holder.price.setText(s.getPrice());

           holder.currency_symbol = (TextView) itemView.findViewById(R.id.currency_symbol);
           holder.currency_symbol.setText(s.getCurrencySymbol());
           holder.total_streamed = (TextView) itemView.findViewById(R.id.total_streamed);
           holder.total_streamed.setText(u.getTotalStreamed());

       }
        return itemView;
    }

    @Override
    public boolean areAllItemsEnabled() {
        return false;
    }

    @Override
    public boolean isEnabled(int position) {
        return false;
    }

    @Override
    public void registerDataSetObserver(DataSetObserver observer) {

    }

    @Override
    public void unregisterDataSetObserver(DataSetObserver observer) {

    }

    @Override
    public int getCount() {
        return response.getCount();
    }

    @Override
    public Object getItem(int position) {
        return response[position];
    }

    @Override
    public long getItemId(int position) {
        return position;
    }

    @Override
    public boolean hasStableIds() {
        return false;
    }

    @Override
    public int getItemViewType(int position) {
        return 0;
    }

    @Override
    public int getViewTypeCount() {
        return 0;
    }

    @Override
    public boolean isEmpty() {
        return false;
    }
}