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初学小白的疑问

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[已解决问题] 解决于 2016-10-31 16:15
package com.fengchuxiaodai.musicplayer;

import java.io.File;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

import com.fengchuxiaodai.bean.Music;
import com.fengchuxiaodai.music.db.MyMusicDao;
import com.lidroid.xutils.ViewUtils;
import com.lidroid.xutils.view.annotation.ViewInject;

import android.media.MediaPlayer;
import android.os.Bundle;
import android.os.Environment;
import android.os.Handler;
import android.os.Message;
import android.app.Activity;
import android.content.Context;
import android.database.Cursor;
import android.util.Log;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
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 final String TAG = "MainActivity";

    private Message msg;
    protected static final int SUCCESSDELETE = 0;
    protected static final int ERRORDELETE = 1;
    protected static final int ITEMDELETE = 2;
    protected static final int FINDMUSIC = 3;

    private static final int SDCARDERROR = 4;

    private ListView lv_main_listview;
    private List<Music> musicList;
    private MediaPlayer mediaPlayer;
    private MyMusicDao myMusicDao;
    private Music music;

    private Handler handler = new Handler() {
        public void handleMessage(Message msg) {
            switch (msg.what) {
            case SUCCESSDELETE:
                Toast.makeText(MainActivity.this, msg.obj + "", 0).show();
                break;
            case ERRORDELETE:
                Toast.makeText(MainActivity.this, msg.obj + "", 0).show();
                break;
            case ITEMDELETE:
                Toast.makeText(MainActivity.this, msg.obj + "", 0).show();
                break;
            case SDCARDERROR:
                Toast.makeText(MainActivity.this, msg.obj + "", 0).show();
                break;

            }
        };
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        lv_main_listview = (ListView) findViewById(R.id.lv_main_listview);
        msg = Message.obtain();
        myMusicDao = new MyMusicDao(MainActivity.this);
        // 每次打开软件先从music表获取所有数据,添加进一个集合,将集合的内容添加进item,在listview中显示出来
        // 如果music表为空,也就是musicList集合长度为0,提示搜索歌曲
        runOnUiThread(new Runnable() {
            @Override
            public void run() {
                musicList = myMusicDao.findAll();
                if (musicList == null || musicList.size() == 0) {
                    findAllMusic();
                }
            }
        });
        // musicList = new ArrayList<Music>()
        lv_main_listview.setAdapter(new MyAdapter());
    }

    protected void findAllMusic() {
        File sdcard = null;
        if (Environment.getExternalStorageState().equals(
                android.os.Environment.MEDIA_MOUNTED)) {
            sdcard = Environment.getExternalStorageDirectory();
            Log.i(TAG, sdcard.getPath());
            musicList = new ArrayList<Music>();
            selectSdcard(sdcard);
        } else {
            msg.what = SDCARDERROR;
            msg.obj = "内存卡不可用";
            handler.sendMessage(msg);
        }

    }

    private void selectSdcard(File sdcard) {//我在部署项目的时候回提示我这个方法有空指针异常   
        Log.i(TAG, sdcard.getPath());
        if (sdcard != null && sdcard.exists()) {
            File[] files = sdcard.listFiles();
            if (files != null) {
                for (File file : files) {
                    Log.i(TAG, file.getPath());
                    if (file != null && file.isDirectory()) {
                        selectSdcard(file);
                    } else {
                        String name = file.getName();
                        String end = name.substring(name.lastIndexOf(".") + 1,
                                name.length());
                        if ("mp3".equalsIgnoreCase(end)) {
                            music = new Music();
                            music.setName(file.getName());
                            music.setPath(file.toString());
                            musicList.add(music);
                        }
                    }
                }
            }
        }
    }

    private class MyAdapter extends BaseAdapter {

        @Override
        public int getCount() {
            // TODO Auto-generated method stub
            return musicList.size();
        }

        @Override
        public View getView(final int position, View convertView,
                ViewGroup parent) {
            ViewHolder holder = null;
            if (convertView == null) {
                convertView = View.inflate(MainActivity.this,
                        R.layout.item_listview, null);
                holder = new ViewHolder(convertView);
                convertView.setTag(holder);
            }
            holder = (ViewHolder) convertView.getTag();
            holder.tv_name.setText(musicList.get(position).getName());
            // 设置点击歌曲的方法
            holder.tv_name.setOnClickListener(new OnClickListener() {

                @Override
                public void onClick(View v) {
                    String path = musicList.get(position).getPath();
                    if (mediaPlayer != null || mediaPlayer.isPlaying()) {
                        mediaPlayer.stop();
                        mediaPlayer.release();
                        mediaPlayer = null;
                    }
                    mediaPlayer = new MediaPlayer();
                    try {
                        mediaPlayer.setDataSource(path);
                        mediaPlayer.prepare();
                        mediaPlayer.start();
                    } catch (IllegalArgumentException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    } catch (SecurityException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    } catch (IllegalStateException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    } catch (IOException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                }
            });
            // 设置点击删除的方法
            holder.tv_delete.setOnClickListener(new OnClickListener() {

                @Override
                public void onClick(View v) {
                    String path = musicList.get(position).getPath();
                    File file = new File(path);
                    if (file.exists()) {
                        Log.i(TAG, "文件存在");
                        if (file.delete()) {
                            Log.i(TAG, "删除成功");
                            msg.obj = "删除成功";
                            msg.what = SUCCESSDELETE;
                        } else {
                            Log.i(TAG, "删除失败");
                            msg.obj = "删除失败";
                            msg.what = ERRORDELETE;
                        }
                    } else {
                        Log.i(TAG, "文件不存在,删除当前记录");
                        msg.obj = "文件不存在,删除当前记录";
                        msg.what = ITEMDELETE;
                    }
                    handler.sendMessage(msg);
                }
            });
            return null;
        }

        @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;
        }

    }

    private class ViewHolder {
        @ViewInject(R.id.tv_name)
        private TextView tv_name;
        @ViewInject(R.id.tv_delete)
        private TextView tv_delete;

        public ViewHolder(View view) {
            ViewUtils.inject(this, view);
        }
    }

}

运行后提示空指针异常  就在遍历内存卡那个方法那里

凤雏小呆的主页 凤雏小呆 | 菜鸟二级 | 园豆:202
提问于:2016-01-22 19:00
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最佳答案
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按道理讲如果只分析selectSdcard方法只有Log.i(TAG, sdcard.getPath());和musicList.add(music);才会报空指针。但是在调该方法时会写日志且初始化musicList,不应该报空指针呀?另外该方法有多处冗余和逻辑问题。

奖励园豆:5
RNN | 菜鸟二级 |园豆:209 | 2016-01-23 22:30
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