Android-关于Cursor空指针的有关问题

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();
		}
	}