得到错误而执行MediaPlayer.start（）方法

Question

我总是得到这个错误： -

m.example.android.miwok E/AndroidRuntime: FATAL EXCEPTION: main 
Process: com.example.android.miwok, PID: 23463 
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.media.MediaPlayer.start()' on a null object reference 
    at com.example.android.miwok.NumbersActivity$1.onItemClick(NumbersActivity.java:46) 
    at android.widget.AdapterView.performItemClick(AdapterView.java:310) 
    at android.widget.AbsListView.performItemClick(AbsListView.java:1188) 
    at android.widget.AbsListView$PerformClick.run(AbsListView.java:3231) 
    at android.widget.AbsListView.onTouchUp(AbsListView.java:4176) 
    at android.widget.AbsListView.onTouchEvent(AbsListView.java:3887) 
    at android.view.View.dispatchTouchEvent(View.java:8593) 
    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2513) 
    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2157) 
    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2519) 
    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2171) 
    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2519) 
    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2171) 
    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2519) 
    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2171) 
    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2519) 
    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2171) 
    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2519) 
    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2171) 
    at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchTouchEvent(PhoneWindow.java:2484) 
    at com.android.internal.policy.impl.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1800) 
    at android.app.Activity.dispatchTouchEvent(Activity.java:2797) 
    at android.support.v7.view.WindowCallbackWrapper.dispatchTouchEvent(WindowCallbackWrapper.java:60) 
    at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:2445) 
    at android.view.View.dispatchPointerEvent(View.java:8799) 
    at android.view.ViewRootImpl$ViewPostImeInputStage.processPointerEvent(ViewRootImpl.java:4662) 
    at android.view.ViewRootImpl$ViewPostImeInputStage.onProcess(ViewRootImpl.java:4520) 
    at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:4034) 
    at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:4087) 
    at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:4053) 
    at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:4190) 
    at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:4061) 
    at android.view.ViewRootImpl$AsyncInputStage.apply(ViewRootImpl.java:4247) 
    at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:4034) 
    at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:4087) 
    at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:4053) 
    at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:4061) 
    at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:4034) 
    at android.view.ViewRootImpl.deliverInputEvent(ViewRootImpl.java:6463) 
    at android.view.ViewRootImpl.doProcessInputEvents(ViewRootImpl.java:6437) 
    at android.view.ViewRootImpl.enqueueInputEvent(ViewRootImpl.java:6390) 
    at android.view.ViewRootImpl$WindowInputEventReceiver.onInputEvent(ViewRootImpl.java:6622) 
    at android.view.InputEventReceiver.dispatchInputEvent(InputEventReceiver.java:185) 
    at android.os.MessageQueue.nativePollOnce(Native Method) 
    at android.os.MessageQueue.next(MessageQueue.java:148) 
    at android.os.Looper.loop(Looper.java:151) 
    at android.app.ActivityThread.main(ActivityThread.java:5649) 
    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:959) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:754) 

这里是我的代码（NumbersActivity）： -

package com.example.android.miwok; 
import android.media.MediaPlayer; 
import android.os.Bundle; 
import android.support.v7.app.AppCompatActivity; 
import android.view.View; 
import android.widget.AdapterView; 
import android.widget.ListView; 

import java.util.ArrayList; 

public class NumbersActivity extends AppCompatActivity{ 

    private MediaPlayer mediaplayer; 

    @Override 
    protected void onCreate(Bundle savedInstanceState) 
    { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_numbers); 

     final ArrayList<word> Word = new ArrayList<>(); 
     Word.add(new word("One","Lutti",R.drawable.number_one, R.raw.number_one)); 
     Word.add(new word("Two","Otiiko",R.drawable.number_two, R.raw.number_two)); 
     Word.add(new word("Three","Tolookosu",R.drawable.number_three, R.raw.number_three)); 
     Word.add(new word("Four","Oyyisa",R.drawable.number_four, R.raw.number_four)); 
     Word.add(new word("Five","Massokka",R.drawable.number_five, R.raw.number_five)); 
     Word.add(new word("Six","Temmokka",R.drawable.number_six, R.raw.number_six)); 
     Word.add(new word("Seven","Kenekaku",R.drawable.number_seven, R.raw.number_seven)); 
     Word.add(new word("Eight","Kawinta",R.drawable.number_eight, R.raw.number_eight)); 
     Word.add(new word("Nine","Wo’e",R.drawable.number_nine, R.raw.number_nine)); 
     Word.add(new word("Ten","Na’aacha",R.drawable.number_ten, R.raw.number_ten)); 

     WordAdapter itemsAdapter = new WordAdapter(this, Word,R.color.category_numbers); 
     ListView listView = (ListView) findViewById(R.id.list_num); 
     listView.setAdapter(itemsAdapter); 

     listView.setOnItemClickListener 
       (new AdapterView.OnItemClickListener() 
       { 
        @Override 
        public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) 
        { 
         word Woord = Word.get(i); 
         mediaplayer.create(NumbersActivity.this, Woord.getAudioSRC()); 
         mediaplayer.start(); 
        } 

       } 
       ); 
    } 
} 

为word.java代码： - 为WordAdapter

package com.example.android.miwok; 


public class word 
{ 

    private String mDefaultTranslation; 
    private String mMiwokTranslation; 
    private int mAudio; 
    private int mImage = NO_IMAGE_PROVIDED ; 
    private static final int NO_IMAGE_PROVIDED = -1; 

    public word(String mdefaultTranslation, String mmiwokTranslation, int mimage, int maudio) 
    { 
     mDefaultTranslation = mdefaultTranslation; 
     mMiwokTranslation = mmiwokTranslation; 
     mImage = mimage; 
     mAudio = maudio; 
    } 

    public word(String mdefaultTranslation, String mmiwokTranslation, int maudio) 
    { 
     mDefaultTranslation = mdefaultTranslation; 
     mMiwokTranslation = mmiwokTranslation; 
     mAudio = maudio; 
    } 

    public String getDefaultTranslation() 
    { 
     return(mDefaultTranslation); 
    } 

    public String getMiwokTranslation() 
    { 
     return(mMiwokTranslation); 
    } 

    public int getImageSRC() {return(mImage);} 

    public boolean hasImage() 
    { 
     return(mImage != NO_IMAGE_PROVIDED); 
    } 

    public int getAudioSRC() {return(mAudio);} 

} 

代码： -

package com.example.android.miwok; 

import android.app.Activity; 
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 java.util.ArrayList; 

/** 
* Created by chhotu lal jain on 09/07/2016. 
*/ 
public class WordAdapter extends ArrayAdapter<word> 
{ 
int ColorPath = -1; 
public WordAdapter(Activity context, ArrayList<word> Wordss, int colorPath) 
{ 
    super(context, 0, Wordss); 
    ColorPath = colorPath; 
} 

@Override 
public View getView(int position, View convertView, ViewGroup parent) 
{ 
    word currentword = getItem(position); 

    View VconvertView = convertView; 
    if(VconvertView == null) 
    { 
     VconvertView = LayoutInflater.from(getContext()).inflate(R.layout.list_item, parent, false); 
    } 

    TextView TV1 = (TextView) VconvertView.findViewById(R.id.miwok_text_view); 
    TV1.setText(currentword.getMiwokTranslation()); 

    TV1 = (TextView) VconvertView.findViewById(R.id.default_text_view); 
    TV1.setText(currentword.getDefaultTranslation()); 

    ImageView IV1 = (ImageView) VconvertView.findViewById(R.id.Image_View); 

    if(currentword.hasImage()) 
    { 
     IV1.setImageResource(currentword.getImageSRC()); 
     IV1.setVisibility(View.VISIBLE); 
    } 
    else 
    { 
     IV1.setVisibility(View.GONE); 
    } 

    View textContainer = VconvertView.findViewById(R.id.text_container); 
    int color = ContextCompat.getColor(getContext(), ColorPath); 
    textContainer.setBackgroundColor(color); 

    return VconvertView; 


} 
} 

我相信其他活动和java文件不是必需的。

*所有的音频文件的ID是100％正确的。

Answer 1

替换：

mediaplayer.create(NumbersActivity.this, Woord.getAudioSRC()); 
mediaplayer.start(); 

与

mediaplayer = Mediaplayer.create(NumbersActivity.this, Woord.getAudioSRC()); 
mediaplayer.start();