在Android应用中读取SD卡文件时程序NullPointerException报错如何解决

本篇文章为大家展示了在Android应用中读取SD卡文件时程序NullPointerException报错如何解决，内容简明扼要并且容易理解，绝对能使你眼前一亮，通过这篇文章的详细介绍希望你能有所收获。

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;    }  }}