读取SD卡文件时抛出NullPointerException

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相关源码：

package com.example.musicplayer;import java.io.File;import java.util.ArrayList;import java.util.List;import android.app.Activity;import android.os.Bundle;import android.os.Environment;import android.view.Menu;import android.view.MenuItem;import android.view.View;import android.view.ViewGroup;import android.widget.BaseAdapter;import android.widget.ListView;import android.widget.TextView;import android.widget.Toast;public class MainActivity extends Activity {    private ListView listView;    private final String path = "/storage/sdcard/mp3/";    private List<String> musicList;    private ViewHolder viewHolder;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        listView = (ListView) findViewById(R.id.lv_music);        Toast.makeText(getApplicationContext(), path, Toast.LENGTH_SHORT).show();        initMusic();    }    private void initMusic() {        File file = new File(path);        File[] files = file.listFiles();        musicList = new ArrayList<String>();        for (File f : files) {            if (f.getName().endsWith(".mp3")) {                musicList.add(f.getAbsolutePath());            }        }        listView.setAdapter(new MusicListAdapter());    }    private class MusicListAdapter extends BaseAdapter{        @Override        public int getCount() {            return musicList.size();        }        @Override        public View getView(int position, View convertView, ViewGroup parent) {            View view = null;            if(convertView == null){                view = View.inflate(getApplicationContext(), R.layout.activity_music_item, null);                viewHolder = new ViewHolder();                viewHolder.musicName = (TextView) view.findViewById(R.id.tv_music_name);            } else {                view = convertView;            }            String path = musicList.get(position);            viewHolder.musicName.setText(path.substring(path.lastIndexOf("/") + 1));            return view;        }        @Override        public Object getItem(int position) {            // TODO Auto-generated method stub            return null;        }        @Override        public long getItemId(int position) {            // TODO Auto-generated method stub            return 0;        }    }}

获取SD卡中MP3文件夹下的文件信息时在foreach时抛出NullPointerException，最后发现是没有添加读取SD卡的权限

<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>

获取SD卡路径：”/mnt/sdcard/” “/storage/sdcard/”

官方推荐：

Environment.getExternalStorageDirectory.getPath();

该方法获取的路径最后没有’/’

"/mnt/sdcard"   "/storage/sdcard"

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