Android实验音乐播放器

好的，Android实验中实现一个音乐播放器可以分为以下几个步骤：

1. 添加权限

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

2. 构建UI

在activity_main.xml文件中添加以下UI控件：

<RelativeLayout
    android:id="@+id/parent_view"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/colorPrimaryDark">

    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerInParent="true"
        android:textColor="@android:color/white"
        android:textSize="24sp"
        android:textStyle="bold" />

    <LinearLayout
        android:id="@+id/control_panel"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:background="@color/colorPrimary">

        <ImageButton
            android:id="@+id/previous_button"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center_vertical"
            android:background="@null"
            android:padding="10dp"
            android:src="@drawable/ic_skip_previous_white_48dp" />

        <ImageButton
            android:id="@+id/play_button"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center_vertical"
            android:background="@null"
            android:padding="10dp"
            android:src="@drawable/ic_play_arrow_white_48dp" />

        <ImageButton
            android:id="@+id/next_button"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center_vertical"
            android:background="@null"
            android:padding="10dp"
            android:src="@drawable/ic_skip_next_white_48dp" />

    </LinearLayout>

</RelativeLayout>

3. 实现音乐播放

在MainActivity.java文件中实现音乐播放功能，包括播放、暂停、上一曲、下一曲等功能。

public class MainActivity extends AppCompatActivity implements View.OnClickListener {

    private MediaPlayer mediaPlayer;
    private ArrayList<String> musicList;
    private int currentIndex = 0;
    private boolean isPlaying = false;
    private Handler handler = new Handler();

    private TextView textView;
    private ImageButton previousButton, playButton, nextButton;

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

        textView = findViewById(R.id.textView);
        previousButton = findViewById(R.id.previous_button);
        playButton = findViewById(R.id.play_button);
        nextButton = findViewById(R.id.next_button);

        previousButton.setOnClickListener(this);
        playButton.setOnClickListener(this);
        nextButton.setOnClickListener(this);

        // 获取音乐列表
        musicList = new ArrayList<>();
        ContentResolver contentResolver = getContentResolver();
        Uri uri = MediaStore.Audio.Media.EXTERNAL_CONTENT_URI;
        Cursor cursor = contentResolver.query(uri, null, null, null, null);
        if (cursor != null && cursor.moveToFirst()) {
            do {
                String path = cursor.getString(cursor.getColumnIndex(MediaStore.Audio.Media.DATA));
                musicList.add(path);
            } while (cursor.moveToNext());
            cursor.close();
        }

        // 初始化MediaPlayer
        mediaPlayer = new MediaPlayer();
        mediaPlayer.setWakeMode(getApplicationContext(), PowerManager.PARTIAL_WAKE_LOCK);
        mediaPlayer.setOnCompletionListener(new MediaPlayer.OnCompletionListener() {
            @Override
            public void onCompletion(MediaPlayer mediaPlayer) {
                playNext();
            }
        });

        // 播放第一首歌
        playMusic(currentIndex);
    }

    @Override
    public void onClick(View view) {
        switch (view.getId()) {
            case R.id.previous_button:
                playPrevious();
                break;
            case R.id.play_button:
                if (isPlaying) {
                    pauseMusic();
                } else {
                    startMusic();
                }
                break;
            case R.id.next_button:
                playNext();
                break;
        }
    }

    private void playMusic(int index) {
        try {
            mediaPlayer.reset();
            mediaPlayer.setDataSource(musicList.get(index));
            mediaPlayer.prepare();
            mediaPlayer.start();
            isPlaying = true;
            updatePlayButton();
            updateTextView();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    private void pauseMusic() {
        mediaPlayer.pause();
        isPlaying = false;
        updatePlayButton();
    }

    private void startMusic() {
        mediaPlayer.start();
        isPlaying = true;
        updatePlayButton();
    }

    private void playPrevious() {
        if (currentIndex > 0) {
            currentIndex--;
            playMusic(currentIndex);
        } else {
            Toast.makeText(this, "已经是第一首歌了", Toast.LENGTH_SHORT).show();
        }
    }

    private void playNext() {
        if (currentIndex < musicList.size() - 1) {
            currentIndex++;
            playMusic(currentIndex);
        } else {
            Toast.makeText(this, "已经是最后一首歌了", Toast.LENGTH_SHORT).show();
        }
    }

    private void updatePlayButton() {
        if (isPlaying) {
            playButton.setImageResource(R.drawable.ic_pause_white_48dp);
        } else {
            playButton.setImageResource(R.drawable.ic_play_arrow_white_48dp);
        }
    }

    private void updateTextView() {
        handler.post(new Runnable() {
            @Override
            public void run() {
                textView.setText(musicList.get(currentIndex));
            }
        });
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        mediaPlayer.stop();
        mediaPlayer.release();
    }
}

4. 运行程序

运行程序，可以看到一个简单的音乐播放器界面，可以通过上一曲、播放/暂停、下一曲按钮进行操作，同时也可以通过列表选择音乐进行播放。