Android 中读取SD卡文件时抛出NullPointerException错误解决办法

Android 中读取SD卡文件时抛出NullPointerException错误解决办法

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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