Android--关于Cursor空指针的问题
最近几天无聊自己动手写个音乐播放器，用到Cursor来取得数据库中音乐文件的
信息，但是当用到Cursor的时候总是报空指针错误，后来发现是模拟器上没有
音乐文件，使用Cursor的时候 ，若Cursor中没有结果，则Cursor的对象则为空
，所以在使用Cursor的时候最好先判断Cursor对象是否为空且其结果是否大于等于1，
以下是最开始的代码：
private void getSongMessage(){String TITLE = MediaStore.Audio.Media.TITLE;String DATA = MediaStore.Audio.Media.DATA;String ALBUM = MediaStore.Audio.Media.ALBUM;String ARTIST = MediaStore.Audio.Media.ARTIST;Uri uri = MediaStore.Audio.Media.EXTERNAL_CONTENT_URI;ContentResolver cr = getContentResolver(); Cursor cs = cr.query(uri, null, null, null, null); while (cs.moveToNext()) {String title = cs.getString(cs.getColumnIndex(TITLE));String data = cs.getString(cs.getColumnIndex(DATA));String album = cs.getString(cs.getColumnIndex(ALBUM));String artist = cs.getString(cs.getColumnIndex(ARTIST));MusicData.title.add(title);MusicData.data.add(data);MusicData.album.add(album);MusicData.artist.add(artist);}}
以下 是修改后的代码：
private void getSongMessage(){String TITLE = MediaStore.Audio.Media.TITLE;String DATA = MediaStore.Audio.Media.DATA;String ALBUM = MediaStore.Audio.Media.ALBUM;String ARTIST = MediaStore.Audio.Media.ARTIST;Uri uri = MediaStore.Audio.Media.EXTERNAL_CONTENT_URI;ContentResolver cr = getContentResolver(); Cursor cs = cr.query(uri, null, null, null, null); if(cs != null && cs.getCount() >= 1){while (cs.moveToNext()) {String title = cs.getString(cs.getColumnIndex(TITLE));String data = cs.getString(cs.getColumnIndex(DATA));String album = cs.getString(cs.getColumnIndex(ALBUM));String artist = cs.getString(cs.getColumnIndex(ARTIST));MusicData.title.add(title);MusicData.data.add(data);MusicData.album.add(album);MusicData.artist.add(artist);}}else{Toast.makeText(this, "No Data", Toast.LENGTH_LONG).show();}}