android - 空对象引用上的 NullPointerException : Attempt to invoke virtual method android. content.Context.getApplicationContext()'

Question

我有一个 Main-Activity，它看起来像:

public class MainActivity extends Activity {

ExpandableListAdapter listAdapter;
ExpandableListView expListView;  
WeaponList listData = new WeaponList();
public static StatusCheck checkBombStatus = new StatusCheck();
String weapon = null;
Intent openGameplay;


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

    setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_PORTRAIT);

    // get the listview
    expListView = (ExpandableListView) findViewById(R.id.expandableListView1);

    // preparing list data
    listData.prepareWeaponList();

    listAdapter = new ExpandableListAdapter(this, listData.listDataHeader, listData.listDataChild);

    // setting list adapter
    expListView.setAdapter(listAdapter);

    //collapse all child-items from the listview
    collapseItems();

    // Listview on child click listener       
    expListView.setOnChildClickListener(new OnChildClickListener() {

        @Override
        public boolean onChildClick(ExpandableListView parent, View v,
                                    int groupPosition, int childPosition, long id) {
            weapon = listData.listDataChild.get(listData.listDataHeader.get(groupPosition)).get(childPosition);

            openGameplay = new Intent(MainActivity.this, GamePlay.class);
            openGameplay.putExtra("weapon", weapon);
            startActivity(openGameplay);

            return false;
        }
    });
}

private void collapseItems() {

    expListView.expandGroup(0);
    expListView.expandGroup(1);
    expListView.expandGroup(2);
    expListView.expandGroup(3);
    expListView.expandGroup(4);
    expListView.expandGroup(5);
    expListView.expandGroup(6);
    expListView.expandGroup(7);
}




public void exitApplication() {
    this.finish();
}

我的第二个 Activity :

public class GamePlay extends Activity {
...
static MediaPlayer mediaPlayer = new MediaPlayer();
static SoundPool soundPool;
static boolean loaded = false;
private static Context mContext;
public static StatusCheck statusCheck;

 public static Context getContext() {
       return mContext;
 }

    public void setContext(Context mContext) {
        GamePlay.mContext = mContext;
 }

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

    setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE);

    Bundle extras = getIntent().getExtras();    

    ....    

    loadweapon(weapon = extras.getString("weapon"));
    loadsound();

    imageView.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View v) {

            if(j == 1) {
                playAudioFromMediaPlayer();

            }

            else {
                //MediaPlayerService.loadAudioToSoundPool(getApplicationContext(), 54);
            }
        }
    });

    reload.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View v) {
            ...
        }
    });
}


private void loadweapon(String weapon) {

    if() ....
}


private void loadsound() {
    if(j == 1 && soundID != 29) {

        loadAudioToMediaPlayer(soundID);
    }
    else {

        loadAudioToSoundPool(soundID);
    }
}


public static void loadAudioToMediaPlayer(int id) {

    soundID = id;
    mediaPlayer = MediaPlayer.create(mContext.getApplicationContext(), SoundList.soundListfire.get(id));
}

public static void loadAudioToSoundPool(int id) {

  soundPool.setOnLoadCompleteListener(new OnLoadCompleteListener() {
      @Override
      public void onLoadComplete(SoundPool soundPool, int sampleId, int status) {
        loaded = true;
      }
});
  soundID = soundPool.load(mContext.getApplicationContext(), SoundList.soundListfire.get(id), 1);
}

....
}

当我点击 Imageview 时出现以下异常:

03-11 12:01:20.199: E/AndroidRuntime(8929): java.lang.RuntimeException: Unable to start activity ComponentInfo{....GamePlay}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.Context android.content.Context.getApplicationContext()' on a null object reference
03-11 12:01:20.199: E/AndroidRuntime(8929):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2329)
03-11 12:01:20.199: E/AndroidRuntime(8929):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2391)
03-11 12:01:20.199: E/AndroidRuntime(8929):     at android.app.ActivityThread.access$900(ActivityThread.java:147)
03-11 12:01:20.199: E/AndroidRuntime(8929):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1296)
03-11 12:01:20.199: E/AndroidRuntime(8929):     at android.os.Handler.dispatchMessage(Handler.java:102)
03-11 12:01:20.199: E/AndroidRuntime(8929):     at android.os.Looper.loop(Looper.java:135)
03-11 12:01:20.199: E/AndroidRuntime(8929):     at android.app.ActivityThread.main(ActivityThread.java:5256)
03-11 12:01:20.199: E/AndroidRuntime(8929):     at java.lang.reflect.Method.invoke(Native Method)
03-11 12:01:20.199: E/AndroidRuntime(8929):     at java.lang.reflect.Method.invoke(Method.java:372)
03-11 12:01:20.199: E/AndroidRuntime(8929):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:898)
03-11 12:01:20.199: E/AndroidRuntime(8929):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:693)
03-11 12:01:20.199: E/AndroidRuntime(8929): Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.Context android.content.Context.getApplicationContext()' on a null object reference
03-11 12:01:20.199: E/AndroidRuntime(8929):     at cs16.tacticalguns.GamePlay.loadAudioToMediaPlayer(GamePlay.java:442)
03-11 12:01:20.199: E/AndroidRuntime(8929):     at cs16.tacticalguns.GamePlay.loadsound(GamePlay.java:423)
03-11 12:01:20.199: E/AndroidRuntime(8929):     at cs16.tacticalguns.GamePlay.onCreate(GamePlay.java:72)
03-11 12:01:20.199: E/AndroidRuntime(8929):     at android.app.Activity.performCreate(Activity.java:5938)
03-11 12:01:20.199: E/AndroidRuntime(8929):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
03-11 12:01:20.199: E/AndroidRuntime(8929):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2282)
03-11 12:01:20.199: E/AndroidRuntime(8929):     ... 10 more

我尝试用 this 或 Gameplay.this 替换 mContext.getApplicationContext()，但是我遇到了错误 Cannot在静态上下文中使用它。我做错了什么，我该如何解决？

Answer 1

通过loadAudioToSoundPool方法传递context参数

private Context mContext;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.gameplay);
    mContext=this;


public static void loadAudioToSoundPool(Context mContext, int id) {

  soundPool.setOnLoadCompleteListener(new OnLoadCompleteListener() {
      @Override
      public void onLoadComplete(SoundPool soundPool, int sampleId, int status) {
        loaded = true;
      }
});
  soundID = soundPool.load(mContext, SoundList.soundListfire.get(id), 1);
}