带有bug的列表视图

Question

我正在开发Soundplayer应用程序，何时在emulater上运行，但它在物理设备上无法运行。点击图标开始的错误，我得到了一个错误，并得到了保证。有人可以看看这个代码吗？ 这里是代码。

SoundPlayList活动@

public class SoundPlayList extends Activity { 
public final static int PLAY_MUSIC = 0; 
private ListView mListView; 

@Override 
public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.soundplayerlist); 

    mListView = (ListView)findViewById(R.id.listView1); 

    SoundPlayerAdapter adapter = new SoundPlayerAdapter(this); 
    mListView.setAdapter(adapter); 

    mListView.setOnItemClickListener(new AdapterView.OnItemClickListener() { 
     public void onItemClick(AdapterView<?> parent,View view,int position,long id){ 
     ListView listView = (ListView)parent; 

     String item = (String)listView.getItemAtPosition(position); 
     Intent intent = new Intent(SoundPlayList.this, SoundPlayerActivity.class); 
     intent.putExtra("id",parent.getItemIdAtPosition(position)); 
     intent.putExtra("name",item); 
     startActivityForResult(intent,PLAY_MUSIC); 

    } 
    }); 

} 

SoundPlayerAdapter @

public class SoundPlayerAdapter extends ArrayAdapter<String>{ 
    private ArrayList<Long> mMusicIds = new ArrayList<Long>(); 
    public SoundPlayerAdapter(Context context) { 
     super(context, android.R.layout.simple_list_item_1); 
     ContentResolver resolver = context.getContentResolver(); 
     Cursor cursor = resolver.query(MediaStore.Audio.Media.EXTERNAL_CONTENT_URI,null,null,null,null); 
    while(cursor.moveToNext()){ 
     String name = cursor.getString(cursor.getColumnIndex(MediaStore.Audio.Media.TITLE)); 
     long id = cursor.getLong(cursor.getColumnIndex(MediaStore.Audio.Media._ID)); 

     mMusicIds.add(id); 

     this.add(name); 

    } 
    } 
    public long getItemId(int position){ 
     return mMusicIds.get(position); 

    } 
} 

} 

日志跟踪@

11-12 15:45:04.985: D/AndroidRuntime(5288): Shutting down VM 
11-12 15:45:04.985: W/dalvikvm(5288): threadid=1: thread exiting with uncaught exception (group=0x2aac8578) 
11-12 15:45:04.985: E/AndroidRuntime(5288): FATAL EXCEPTION: main 
11-12 15:45:04.985: E/AndroidRuntime(5288): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.soundplayer/com.example.soundplayer.SoundPlayList}: java.lang.NullPointerException 
11-12 15:45:04.985: E/AndroidRuntime(5288):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1659) 
11-12 15:45:04.985: E/AndroidRuntime(5288):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1675) 
11-12 15:45:04.985: E/AndroidRuntime(5288):  at android.app.ActivityThread.access$1500(ActivityThread.java:121) 
11-12 15:45:04.985: E/AndroidRuntime(5288):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:943) 
11-12 15:45:04.985: E/AndroidRuntime(5288):  at android.os.Handler.dispatchMessage(Handler.java:99) 
11-12 15:45:04.985: E/AndroidRuntime(5288):  at android.os.Looper.loop(Looper.java:130) 
11-12 15:45:04.985: E/AndroidRuntime(5288):  at android.app.ActivityThread.main(ActivityThread.java:3701) 
11-12 15:45:04.985: E/AndroidRuntime(5288):  at java.lang.reflect.Method.invokeNative(Native Method) 
11-12 15:45:04.985: E/AndroidRuntime(5288):  at java.lang.reflect.Method.invoke(Method.java:507) 
11-12 15:45:04.985: E/AndroidRuntime(5288):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:866) 
11-12 15:45:04.985: E/AndroidRuntime(5288):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:624) 
11-12 15:45:04.985: E/AndroidRuntime(5288):  at dalvik.system.NativeStart.main(Native Method) 
11-12 15:45:04.985: E/AndroidRuntime(5288): Caused by: java.lang.NullPointerException 
11-12 15:45:04.985: E/AndroidRuntime(5288):  at com.example.soundplayer.SoundPlayList$SoundPlayerAdapter.<init>(SoundPlayList.java:52) 
11-12 15:45:04.985: E/AndroidRuntime(5288):  at com.example.soundplayer.SoundPlayList.onCreate(SoundPlayList.java:29) 
11-12 15:45:04.985: E/AndroidRuntime(5288):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 
11-12 15:45:04.985: E/AndroidRuntime(5288):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1623) 
11-12 15:45:04.985: E/AndroidRuntime(5288):  ... 11 more 
11-12 15:45:10.105: I/Process(5288): Sending signal. PID: 5288 SIG: 9 

Answer 1

11-12 15:45:04.985: E/AndroidRuntime(5288): Caused by: java.lang.NullPointerException 
11-12 15:45:04.985: E/AndroidRuntime(5288): at com.example.soundplayer.SoundPlayList$SoundPlayerAdapter.(SoundPlayList.java:52) 
11-12 15:45:04.985: E/AndroidRuntime(5288): at com.example.soundplayer.SoundPlayList.onCreate(SoundPlayList.java:29) 
11-12 15:45:04.985: E/AndroidRuntime(5288): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 
11-12 15:45:04.985: E/AndroidRuntime(5288): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1623) 
11-12 15:45:04.985: E/AndroidRuntime(5288): ... 11 more 
11-12 15:45:10.105: I/Process(5288): Sending signal. PID: 5288 SIG: 9 

根据日志信息，请参阅SoundPlayList.java:29文件。

EDIT：

ContentResolver.query方法可以返回null。所以你需要NullPoint检查。