Question

我已经将代码从活动转移到片段，我有一个完美的simillar应用程序，我检查了每个sentance，看起来一切都匹配，但遇到了这个问题，。

实际错误：

                                                                     Process: com.example.android.miwok, PID: 7432
                                                                     java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.android.miwok/com.example.android.miwok.Numbers_activity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference
                                                                         at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2927)
                                                                         at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2988)
                                                                         at android.app.ActivityThread.-wrap14(ActivityThread.java)
                                                                         at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1631)
                                                                         at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                         at android.os.Looper.loop(Looper.java:154)
                                                                         at android.app.ActivityThread.main(ActivityThread.java:6682)
                                                                         at java.lang.reflect.Method.invoke(Native Method)
                                                                         at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1520)
                                                                         at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1410)
                                                                      Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference
                                                                         at com.example.android.miwok.numeriuFragmentai.onCreateView(numeriuFragmentai.java:81)
                                                                         at android.support.v4.app.Fragment.performCreateView(Fragment.java:1974)
                                                                         at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1067)
                                                                         at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1252)
                                                                         at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:742)
                                                                         at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1617)
                                                                         at android.support.v4.app.FragmentController.execPendingActions(FragmentController.java:339)
                                                                         at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:602)
                                                                         at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1256)
                                                                         at android.app.Activity.performStart(Activity.java:6959)
                                                                         at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2890)
                                                                         at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2988) 
                                                                         at android.app.ActivityThread.-wrap14(ActivityThread.java) 
                                                                         at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1631) 
                                                                         at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                                         at android.os.Looper.loop(Looper.java:154) 
                                                                         at android.app.ActivityThread.main(ActivityThread.java:6682) 
                                                                         at java.lang.reflect.Method.invoke(Native Method) 
                                                                         at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1520) 
                                                                         at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1410)

用其他simillar代码检查一切都匹配，但我确定我错过了一些东西。

numeriuFragmentai.java

package com.example.android.miwok;


import android.content.Context;
import android.media.AudioManager;
import android.media.MediaPlayer;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.ListView;
import com.example.android.miwok.word;
import com.example.android.miwok.Adaptoreditor;
import android.view.LayoutInflater;
import java.util.ArrayList;

import static com.example.android.miwok.R.id.container;


public class numeriuFragmentai extends Fragment {

private MediaPlayer mMediaPlayer;

private AudioManager mAudio;

private AudioManager.OnAudioFocusChangeListener focuslistener = new AudioManager.OnAudioFocusChangeListener() {
    @Override
    public void onAudioFocusChange(int focusChange) {
        if (focusChange==AudioManager.AUDIOFOCUS_LOSS_TRANSIENT || focusChange == AudioManager.AUDIOFOCUS_LOSS_TRANSIENT_CAN_DUCK)
        {
            mMediaPlayer.pause();
            mMediaPlayer.seekTo(0);
        }
        else if (focusChange==AudioManager.AUDIOFOCUS_GAIN)
        {
            mMediaPlayer.start();
        }
        else if (focusChange==AudioManager.AUDIOFOCUS_LOSS)
        {
            releaseMediaPlayer();
        }
    }
};
private MediaPlayer.OnCompletionListener completed = new MediaPlayer.OnCompletionListener() {
    @Override
    public void onCompletion(MediaPlayer mediaPlayer) {
        releaseMediaPlayer();
    }
};
public numeriuFragmentai() {

}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {

    View rootView = inflater.inflate(R.layout.list_item, container, false);

    mAudio=(AudioManager)getActivity().getSystemService(Context.AUDIO_SERVICE);

    final ArrayList<word> numbers = new ArrayList<word>();
    numbers.add(new word(R.string.number_one, R.string.miwok_number_one,R.drawable.yplay, R.raw.number_one, R.drawable.number_one));
    numbers.add(new word(R.string.number_two, R.string.miwok_number_two,R.drawable.yplay, R.raw.number_two, R.drawable.number_two));
    numbers.add(new word(R.string.number_three, R.string.miwok_number_three,R.drawable.yplay, R.raw.number_three, R.drawable.number_three));
    numbers.add(new word(R.string.number_four, R.string.miwok_number_four,R.drawable.yplay, R.raw.number_four, R.drawable.number_four));
    numbers.add(new word(R.string.number_five, R.string.miwok_number_five, R.drawable.yplay, R.raw.number_five, R.drawable.number_five));
    numbers.add(new word(R.string.number_six, R.string.miwok_number_six,R.drawable.yplay, R.raw.number_six, R.drawable.number_six));
    numbers.add(new word(R.string.number_seven, R.string.miwok_number_seven,R.drawable.yplay, R.raw.number_seven, R.drawable.number_seven));
    numbers.add(new word(R.string.number_eight, R.string.miwok_number_eight,R.drawable.yplay, R.raw.number_eight, R.drawable.number_eight));
    numbers.add(new word(R.string.number_nine, R.string.miwok_number_nine,R.drawable.yplay, R.raw.number_nine, R.drawable.number_nine));
    numbers.add(new word(R.string.number_ten, R.string.miwok_number_ten,R.drawable.yplay, R.raw.number_ten, R.drawable.number_ten));

    Adaptoreditor adapteris = new Adaptoreditor(getActivity(), numbers, R.color.numeriai);

    Adaptoreditor adapter = new Adaptoreditor(getActivity(), numbers, R.color.spalvos);

    ListView listView = (ListView) rootView.findViewById(R.id.list);

    listView.setAdapter(adapter);

    listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> adapterView, View view, int position, long l) {

            releaseMediaPlayer();

            word words = numbers.get(position);

            int result = mAudio.requestAudioFocus(focuslistener, AudioManager.STREAM_MUSIC, AudioManager.AUDIOFOCUS_GAIN_TRANSIENT);

            if (result == AudioManager.AUDIOFOCUS_REQUEST_GRANTED) {

                mMediaPlayer = MediaPlayer.create(getActivity(), words.getSound());
                mMediaPlayer.start();
                mMediaPlayer.setOnCompletionListener(completed);
            }
        }
    });

    return rootView;
}
@Override
public void onStop() {
    super.onStop();
    releaseMediaPlayer();
}
private void releaseMediaPlayer()
{
    if (mMediaPlayer!=null)
    {
        mMediaPlayer.release();
        mMediaPlayer=null;
        mAudio.abandonAudioFocus(focuslistener);
    }
}
}

NumbersActivity.java

package com.example.android.miwok;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;

public class Numbers_activity extends AppCompatActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_category);
    getSupportFragmentManager().beginTransaction()
            .replace(R.id.container, new numeriuFragmentai())
            .commit();
}
}

Adaptoreditor.java

package com.example.android.miwok;

import android.content.Context;
import android.support.v4.content.ContextCompat;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
import android.widget.TextView;
import com.example.android.miwok.word;

import java.util.ArrayList;

public class Adaptoreditor extends ArrayAdapter<word> {

    private int mcolorid;

    public Adaptoreditor(Context context, ArrayList<word> word, int colorid) {

        super(context, 0, word);
        mcolorid=colorid;
    }
    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        View listItemView = convertView;
        if(listItemView == null) {
            listItemView = LayoutInflater.from(getContext()).inflate(R.layout.list_item, parent, false);
        }
        word vertimas = getItem(position);

        TextView nameTextView = (TextView) listItemView.findViewById(R.id.first);
        nameTextView.setText(vertimas.getMiwok());

        TextView numberTextView = (TextView) listItemView.findViewById(R.id.second);

        numberTextView.setText(vertimas.getTranslated());

        ImageView img = (ImageView) listItemView.findViewById(R.id.img);

        if (vertimas.yrft()) {

            img.setImageResource(vertimas.getImgR());
            img.setVisibility(View.VISIBLE);
        } else {

            img.setVisibility(View.GONE);
        }

        ImageView pic = (ImageView)listItemView.findViewById(R.id.player);
        pic.setImageResource(vertimas.getPlayImg());

        View vieta = listItemView.findViewById(R.id.linearas);
        int color = ContextCompat.getColor(getContext(), mcolorid);
        vieta.setBackgroundColor(color);

        return listItemView;
    }
}

word.java

package com.example.android.miwok;


public class word {

   private int mtranslated;

   private  int mmiwok;

    private int mimgid=NER_FOTO;

    private int mpImg;

    private int mSound;

    public final static int NER_FOTO = -1;

    public word (int translated, int miwok, int pimg,int sound)
    {
        mtranslated = translated;
        mmiwok=miwok;
        mpImg=pimg;
        mSound=sound;
    }
    public word (int translated, int miwok,int pimg, int sound,int imgid)
    {
        mtranslated = translated;
        mmiwok=miwok;
        mimgid=imgid;
        mpImg=pimg;
        mSound=sound;
    }
    public int getMiwok()
    {
        return mmiwok;
    }
    public int getTranslated()
    {
        return mtranslated;
    }
    public int getSound(){return  mSound;}
    public int getImgR ()
    {
        return mimgid;
    }
    public int getPlayImg ()
    {
        return mpImg;
    }
    public boolean yrft ()
    {
        return mimgid !=NER_FOTO;
    }
}

activity_category.XML

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

List_item.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:layout_width="match_parent"
    android:layout_height="88dp"
    android:id="@+id/linearas"
    android:background="?android:attr/selectableItemBackground">

    <ImageView
    android:layout_width="32dp"
    android:layout_height="40dp"
    android:src="@mipmap/ic_launcher"
    android:layout_centerInParent="true"
    android:layout_alignParentRight="true"
    android:layout_marginRight="8dp"
    android:id="@+id/player"/>
<LinearLayout
    android:orientation="horizontal"
    android:layout_width="wrap_content"
    android:layout_height="88dp"
    android:layout_alignParentTop="true"
    android:layout_alignParentLeft="true"
    android:layout_alignParentStart="true">
    <ImageView
        android:layout_width="88dp"
        android:layout_height="88dp"
        tools:src="@mipmap/ic_launcher"
        android:id="@+id/img"
        />

<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:gravity="center_vertical"
    android:paddingLeft="16dp">

        <TextView
            android:id="@+id/first"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:textStyle="bold"
            tools:text="Pirmas" />

        <TextView
            android:id="@+id/second"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            tools:text="Antras" />
</LinearLayout>
</LinearLayout>
</RelativeLayout

Wordlist.XML

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

链接到整个应用 App

Answer 1

引起：java.lang.NullPointerException：尝试调用虚拟方法＆＃39;无效 android.widget.ListView.setAdapter（android.widget.ListAdapter）＆＃39;在...上 null对象引用

指向

listView.setAdapter(adapter);

这意味着这是不正确的

ListView listView = (ListView) rootView.findViewById(R.id.list);

因为您的rootView使用了错误的布局

View rootView = inflater.inflate(R.layout.list_item, container, false);

您的R.layout.list_item似乎是针对列表项目...正确的引用应该是R.layout.wordlist？

ListView setAdapter on null object reference

1 个答案: