发布于 2017-08-18 20:58:04 | 124 次阅读 | 评论: 0 | 来源: 网友投递
Android移动端操作系统
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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"感谢阅读，希望能帮助到大家，谢谢大家对本站的支持！