Android:Java.NullPointerException在我的应用程序上出错
我是新来的,但我每天都在这个论坛上读问题。 我正在基于左侧的侧抽屉(使用库“simple side drawer”)构建一个音乐播放器,当我触摸操作栏上的向上按钮时,左抽屉打开。 在左边的抽屉里有一个列表视图(简单),上面有你所有的歌曲。当我点击一个项目时,它应该开始播放…但是应用程序崩溃了。 这就是错误所在Android:Java.NullPointerException在我的应用程序上出错,java,android,eclipse,listview,nullpointerexception,Java,Android,Eclipse,Listview,Nullpointerexception,我是新来的,但我每天都在这个论坛上读问题。 我正在基于左侧的侧抽屉(使用库“simple side drawer”)构建一个音乐播放器,当我触摸操作栏上的向上按钮时,左抽屉打开。 在左边的抽屉里有一个列表视图(简单),上面有你所有的歌曲。当我点击一个项目时,它应该开始播放…但是应用程序崩溃了。 这就是错误所在 12-08 14:33:58.760: E/AndroidRuntime(12420): FATAL EXCEPTION: main 12-08 14:33:58.760: E/Andro
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();
为什么当我尝试播放某个东西时应用程序会崩溃?请帮助我:(:)这是因为您的
mAudioPath
成员为null。请确保在调用onItemClick()
所有其他事情放在一边之前进行设置,您的NullPointerException from onItemClick()方法可能会在以下情况下发生:
playSong(mAudioPath[arg2]);
原因是mAudioPath未初始化且为空。为什么
您已在类Maincu中将其声明为字段,如下所示:
private String[] mAudioPath;
您认为是通过调用getAudioList()来初始化它,但在此方法中,您声明:
String[] mAudioPath = new String[count];
这会隐藏全局变量mAudioPath,因此将初始化本地mAudioPath,而不是用于播放歌曲的全局mAudioPath。要修复此问题,请在getAudioList()中更改:
致:
java.lang.NullPointerException 12-08 14:33:58.760:E/AndroidRuntime(12420):在com.xand.holomiscplayer.Maincu$1.onItemClick(Maincu.java:58)
第58行是什么?看起来gahfy是对的。在哪里初始化和设置mAudioPath?}catch(IOE异常){否。该行不会导致此异常。可能是您发布的代码与运行该行并获取异常时的代码不完全相同,可能是您计算的行数不正确,也可能是您没有了解到IDE编辑器在状态栏中显示了行号。
String[] mAudioPath = new String[count];
String[] mAudioPath = new String[count];
mAudioPath = new String[count];