Android：Java.NullPointerException在我的应用程序错误

我在这里是新的，但我每天都在这个论坛上阅读的问题。我正在建立一个基于左侧抽屉的音乐播放器（使用库“简单侧抽屉”），当我触摸向上按钮（在动作栏上）时，左侧抽屉打开。在左侧抽屉处是一个列表视图（简单）与你的所有的歌。当我在一个项目挖掘那么就应该开始播放......但应用程序崩溃。这是错误Android：Java.NullPointerException在我的应用程序错误

12-08 14:33:58.760: E/AndroidRuntime(12420): FATAL EXCEPTION: main 
12-08 14:33:58.760: E/AndroidRuntime(12420): java.lang.NullPointerException 
12-08 14:33:58.760: E/AndroidRuntime(12420): at com.xand.holomusicplayer.Maincu$1.onItemClick(Maincu.java:58) 
12-08 14:33:58.760: E/AndroidRuntime(12420): at android.widget.AdapterView.performItemClick(AdapterView.java:297) 
12-08 14:33:58.760: E/AndroidRuntime(12420): at android.widget.AbsListView.performItemClick(AbsListView.java:1123) 
12-08 14:33:58.760: E/AndroidRuntime(12420): at android.widget.AbsListView$PerformClick.run(AbsListView.java:2931) 
12-08 14:33:58.760: E/AndroidRuntime(12420): at android.widget.AbsListView$2.run(AbsListView.java:3616) 
12-08 14:33:58.760: E/AndroidRuntime(12420): at android.os.Handler.handleCallback(Handler.java:730) 
12-08 14:33:58.760: E/AndroidRuntime(12420): at android.os.Handler.dispatchMessage(Handler.java:92) 
12-08 14:33:58.760: E/AndroidRuntime(12420): at android.os.Looper.loop(Looper.java:137) 
12-08 14:33:58.760: E/AndroidRuntime(12420): at android.app.ActivityThread.main(ActivityThread.java:5287) 
12-08 14:33:58.760: E/AndroidRuntime(12420): at java.lang.reflect.Method.invokeNative(Native Method) 
12-08 14:33:58.760: E/AndroidRuntime(12420): at java.lang.reflect.Method.invoke(Method.java:525) 
12-08 14:33:58.760: E/AndroidRuntime(12420): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:738) 
12-08 14:33:58.760: E/AndroidRuntime(12420): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:554) 
12-08 14:33:58.760: E/AndroidRuntime(12420): at dalvik.system.NativeStart.main(Native Method)

我不知道为什么，这是代码：

private String[] mAudioPath; 
private MediaPlayer mMediaPlayer; 
private String[] mMusicList; 
private SimpleSideDrawer mSlidingMenu; 
ListView list; 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.main_activity); 
    getActionBar().setDisplayHomeAsUpEnabled(true); 
    mSlidingMenu = new SimpleSideDrawer(this); 
    mSlidingMenu.setLeftBehindContentView(R.layout.playlist); 
    list = (ListView) findViewById (R.id.listView1); 
    mMediaPlayer = new MediaPlayer(); 
    mMusicList = getAudioList(); 
    ArrayAdapter<String> mAdapter = new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1, mMusicList); 
    list.setAdapter(mAdapter); 
    list.setOnItemClickListener(new OnItemClickListener() { 

     @Override 
     public void onItemClick(AdapterView<?> arg0, View arg1, int arg2, 
     long arg3) { 
     try { 
      playSong(mAudioPath[arg2]); 
     } catch (IllegalArgumentException e) { 
      e.printStackTrace(); 
     } catch (IllegalStateException e) { 
      e.printStackTrace(); 
     } catch (IOException e) { 
      e.printStackTrace(); 
     } 
     } 
     }); 
    } 
private String[] getAudioList() { 
    final Cursor mCursor = getContentResolver().query(
      MediaStore.Audio.Media.EXTERNAL_CONTENT_URI, 
      new String[] { MediaStore.Audio.Media.DISPLAY_NAME, MediaStore.Audio.Media.DATA }, null, null, 
      "LOWER(" + MediaStore.Audio.Media.TITLE + ") ASC"); 

    int count = mCursor.getCount(); 

    String[] songs = new String[count]; 
    String[] mAudioPath = new String[count]; 
    int i = 0; 
    if (mCursor.moveToFirst()) { 
     do { 
      songs[i] = mCursor.getString(mCursor.getColumnIndexOrThrow(MediaStore.Audio.Media.DISPLAY_NAME)); 
      mAudioPath[i] = mCursor.getString(mCursor.getColumnIndexOrThrow(MediaStore.Audio.Media.DATA)); 
      i++; 
     } while (mCursor.moveToNext()); 
    } 

    mCursor.close(); 

    return songs; 
} 

private void playSong(String path) throws IllegalArgumentException, 
IllegalStateException, IOException { 

Log.d("ringtone", "playSong :: " + path); 

mMediaPlayer.reset(); 
mMediaPlayer.setDataSource(path);  
mMediaPlayer.prepare(); 
mMediaPlayer.start();

}

@Override 
public boolean onOptionsItemSelected(MenuItem item) { 
    switch (item.getItemId()) { 
    // Respond to the action bar's Up/Home button 
    case android.R.id.home: 
     mSlidingMenu.toggleLeftDrawer(); 
     return true; 
    } 
    return super.onOptionsItemSelected(item); 
} 
}

为什么当我尝试播放某些内容时应用程序崩溃？请帮助我:(:)

来源

2013-12-08 XandaPPds

'显示java.lang.NullPointerException 12-08 14：33：58.760：E/AndroidRuntime（12420）：在com.xand.holomusicplayer.Maincu $ 1.onItemClick（Maincu.java:58）'第58行是什么？看起来gahfy是对的。你在哪里初始化并设置mAudioPath？ – Simon

} catch（IOException e）{ – XandaPPds

Nope。该行不会导致此异常。您发布的代码与运行代码时出现的错误并不完全相同，您得到的错误数字不正确，或者您还没有得知IDE编辑器在状态栏中显示行号。 – Simon

所有其他的事情，从onItemClick您的NullPointerException（）当你的方法可能会发生：

playSong(mAudioPath[arg2]);

这样做的原因是，mAudioPath未初始化和空。为什么？

你已经宣布它作为你的类Maincu一个字段：

private String[] mAudioPath;

你以为你是通过调用getAudioList（）初始化，但是，这个方法里面，您声明：

String[] mAudioPath = new String[count];

其中SHADOWS你的全局变量mAudioPath，所以你的本地mAudioPath被初始化，而不是全局的，然后用于播放歌曲。要解决，你的getAudioList（），更改：

String[] mAudioPath = new String[count];

到：

mAudioPath = new String[count];

来源

2013-12-08 17:05:09 Melquiades

这是因为您的mAudioPath成员为空。请务必在致电onItemClick()之前进行设置。抛开

来源

2013-12-08 14:03:53 gahfy

请告诉我更多 – XandaPPds

Android：Java.NullPointerException在我的应用程序错误

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