用android写一个简单的音乐播放器

好的，下面是一个简单的 Android 音乐播放器的示例代码：

1. 首先，在 AndroidManifest.xml 文件中添加以下权限：

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

2. 创建布局文件 activity_main.xml，包含一个 ListView 和一个 Button：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >
    
    <ListView
        android:id="@+id/listView"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1" />
    
    <Button
        android:id="@+id/buttonPlay"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Play" />
    
</LinearLayout>

3. 创建自定义适配器 MusicListAdapter.java，用于在 ListView 中显示音乐列表：

public class MusicListAdapter extends BaseAdapter {

    private Context mContext;
    private ArrayList<Music> mMusicList;

    public MusicListAdapter(Context context, ArrayList<Music> musicList) {
        mContext = context;
        mMusicList = musicList;
    }

    @Override
    public int getCount() {
        return mMusicList.size();
    }

    @Override
    public Object getItem(int position) {
        return mMusicList.get(position);
    }

    @Override
    public long getItemId(int position) {
        return position;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        if (convertView == null) {
            convertView = LayoutInflater.from(mContext).inflate(android.R.layout.simple_list_item_1, parent, false);
        }

        TextView textView = convertView.findViewById(android.R.id.text1);
        textView.setText(mMusicList.get(position).getTitle());

        return convertView;
    }
}

4. 创建实体类 Music.java，表示一首歌曲：

public class Music {

    private String mTitle;
    private String mPath;

    public Music(String title, String path) {
        mTitle = title;
        mPath = path;
    }

    public String getTitle() {
        return mTitle;
    }

    public String getPath() {
        return mPath;
    }
}

5. 在 MainActivity.java 中实现音乐播放器的逻辑：

public class MainActivity extends AppCompatActivity implements View.OnClickListener {

    private ListView mListView;
    private Button mButtonPlay;

    private ArrayList<Music> mMusicList;
    private MediaPlayer mMediaPlayer;
    private int mCurrentPosition;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mListView = findViewById(R.id.listView);
        mButtonPlay = findViewById(R.id.buttonPlay);
        mButtonPlay.setOnClickListener(this);

        mMusicList = new ArrayList<>();
        loadMusicList();

        MusicListAdapter adapter = new MusicListAdapter(this, mMusicList);
        mListView.setAdapter(adapter);
        mListView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                mCurrentPosition = position;
                playMusic(mMusicList.get(position).getPath());
            }
        });
    }

    @Override
    public void onClick(View v) {
        if (v.getId() == R.id.buttonPlay) {
            if (mMediaPlayer != null && mMediaPlayer.isPlaying()) {
                mMediaPlayer.pause();
                mButtonPlay.setText("Play");
            } else {
                if (mMediaPlayer != null) {
                    mMediaPlayer.start();
                    mButtonPlay.setText("Pause");
                } else {
                    if (mMusicList.size() > 0) {
                        mCurrentPosition = 0;
                        playMusic(mMusicList.get(0).getPath());
                    }
                }
            }
        }
    }

    private void loadMusicList() {
        String[] projection = {MediaStore.Audio.Media.TITLE, MediaStore.Audio.Media.DATA};
        Cursor cursor = getContentResolver().query(MediaStore.Audio.Media.EXTERNAL_CONTENT_URI, projection, null, null, null);
        if (cursor != null && cursor.moveToFirst()) {
            do {
                String title = cursor.getString(cursor.getColumnIndex(MediaStore.Audio.Media.TITLE));
                String path = cursor.getString(cursor.getColumnIndex(MediaStore.Audio.Media.DATA));
                mMusicList.add(new Music(title, path));
            } while (cursor.moveToNext());
            cursor.close();
        }
    }

    private void playMusic(String path) {
        mMediaPlayer = new MediaPlayer();
        try {
            mMediaPlayer.setDataSource(path);
            mMediaPlayer.prepare();
            mMediaPlayer.start();
            mButtonPlay.setText("Pause");
            mMediaPlayer.setOnCompletionListener(new MediaPlayer.OnCompletionListener() {
                @Override
                public void onCompletion(MediaPlayer mp) {
                    mCurrentPosition++;
                    if (mCurrentPosition >= mMusicList.size()) {
                        mCurrentPosition = 0;
                    }
                    playMusic(mMusicList.get(mCurrentPosition).getPath());
                }
            });
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        if (mMediaPlayer != null) {
            mMediaPlayer.release();
            mMediaPlayer = null;
        }
    }
}

6. 运行应用程序，点击列表中的歌曲即可播放，点击播放按钮可以切换播放和暂停状态。