移动开发音乐播放器

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <ImageView
        android:id="@+id/cover"
        android:layout_width="match_parent"
        android:layout_height="600dp"
        android:layout_weight="1"
        android:src="@drawable/composer" />

    <LinearLayout
        android:orientation="vertical"
        android:layout_width="match_parent"
        android:layout_height="300dp"
        android:layout_weight="1">

        <TextView
            android:id="@+id/title"
            android:layout_width="match_parent"
            android:layout_height="20dp"
            android:layout_weight="1"
            android:ellipsize="marquee"
            android:marqueeRepeatLimit="marquee_forever"
            android:text="歌曲名"
            android:gravity="center"
            android:textColor="#000000"
            android:textSize="30dp" />

        <TextView
            android:id="@+id/author"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:gravity="center"
            android:text="艺术家"
            android:textSize="20dp" />
    </LinearLayout>


    <LinearLayout
        android:orientation="horizontal"
        android:layout_width="match_parent"
        android:layout_height="90dp"
        android:gravity="center"
        android:layout_marginBottom="10dp">
        <ImageButton
            android:id="@+id/pre"
            android:layout_width="wrap_content"

            android:layout_height="wrap_content"
            android:src="@drawable/pre"
            android:background="#FFFFFF"/>
        <ImageButton
            android:id="@+id/play"
            android:layout_width="wrap_content"

            android:layout_height="wrap_content"
            android:src="@drawable/play"
            android:background="#FFFFFF"/>
        <ImageButton
            android:id="@+id/next"
            android:layout_width="wrap_content"

            android:layout_height="wrap_content"
            android:src="@drawable/next"
            android:background="#FFFFFF"/>
        <ImageButton
            android:id="@+id/stop"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:src="@drawable/stop"
            android:background="#FFFFFF"/>
    </LinearLayout>
</LinearLayout>

package com.example.mymusicbox;

import android.app.Service;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.content.res.AssetFileDescriptor;
import android.content.res.AssetManager;
import android.media.MediaPlayer;
import android.media.MediaPlayer.OnCompletionListener;
import android.os.IBinder;

import java.io.IOException;

public class MusicService extends Service
{
    MyReceiver serviceReceiver;
    AssetManager am;
    String[] musics = new String[] { "composer.mp3" +
            "", "bridge.mp3",
            "graininear.mp3" };
    MediaPlayer mPlayer;
    // 当前的状态，0x11代表没有播放；0x12代表正在播放；0x13代表暂停
    int status = 0x11;
    // 记录当前正在播放的音乐
    int current = 0;
    @Override
    public IBinder onBind(Intent intent)
    {
        return null;
    }
    @Override
    public void onCreate()
    {
        super.onCreate();
        am = getAssets();
        // 创建BroadcastReceiver
        serviceReceiver = new MyReceiver();
        // 创建IntentFilter
        IntentFilter filter = new IntentFilter();
        filter.addAction(MainActivity.CTL_ACTION);
        registerReceiver(serviceReceiver, filter);
        // 创建MediaPlayer
        mPlayer = new MediaPlayer();
        // 为MediaPlayer播放完成事件绑定监听器
        mPlayer.setOnCompletionListener(new OnCompletionListener() // ①
        {
            @Override
            public void onCompletion(MediaPlayer mp)
            {
                current++;
                if (current >= 3)
                {
                    current = 0;
                }
                //发送广播通知Activity更改文本框
                Intent sendIntent = new Intent(MainActivity.UPDATE_ACTION);
                sendIntent.putExtra("current", current);
                // 发送广播，将被Activity组件中的BroadcastReceiver接收到
                sendBroadcast(sendIntent);
                // 准备并播放音乐
                prepareAndPlay(musics[current]);
            }
        });
    }
    public class MyReceiver extends BroadcastReceiver
    {
        @Override
        public void onReceive(final Context context, Intent intent)
        {
            int control = intent.getIntExtra("control", -1);
            switch (control)
            {
                // 播放或暂停
                case 1:
                    // 原来处于没有播放状态
                    if (status == 0x11)
                    {
                        // 准备并播放音乐
                        prepareAndPlay(musics[current]);
                        status = 0x12;
                    }
                    // 原来处于播放状态
                    else if (status == 0x12)
                    {
                        // 暂停
                        mPlayer.pause();
                        // 改变为暂停状态
                        status = 0x13;
                    }
                    // 原来处于暂停状态
                    else if (status == 0x13)
                    {
                        // 播放
                        mPlayer.start();
                        // 改变状态
                        status = 0x12;
                    }
                    break;
                // 停止声音
                case 2:
                    // 如果原来正在播放或暂停
                    if (status == 0x12 || status == 0x13)
                    {
                        // 停止播放
                        mPlayer.stop();
                        status = 0x11;
                    }
                case 3:
                    current--;
                    if(current < 0)
                        current = 0;
                    prepareAndPlay(musics[current]);
                case 4:
                    current++;
                    if(current > musics.length-1)
                        current = 0;
                    prepareAndPlay(musics[current]);
            }
            // 广播通知Activity更改图标、文本框
            Intent sendIntent = new Intent(MainActivity.UPDATE_ACTION);
            sendIntent.putExtra("update", status);
            sendIntent.putExtra("current", current);
            // 发送广播，将被Activity组件中的BroadcastReceiver接收到
            sendBroadcast(sendIntent);
        }
    }
    private void prepareAndPlay(String music)
    {
        try
        {
            // 打开指定音乐文件
            AssetFileDescriptor afd = am.openFd(music);
            mPlayer.reset();
            // 使用MediaPlayer加载指定的声音文件。
            mPlayer.setDataSource(afd.getFileDescriptor(),
                    afd.getStartOffset(), afd.getLength());
            // 准备声音
            mPlayer.prepare();
            // 播放
            mPlayer.start();
        }
        catch (IOException e)
        {
            e.printStackTrace();
        }
    }
}

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.mymusicbox">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

        <service android:name=".MusicService">
        </service>
    </application>

</manifest>

package com.example.mymusicbox;
import android.support.v4.app.*;
import android.os.Bundle;

import android.app.Activity;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.ImageButton;
import android.widget.ImageView;
import android.widget.TextView;

public class MainActivity extends Activity implements OnClickListener
{
    // 获取界面中显示歌曲标题、作者文本框
    TextView title, author;
    // 播放/暂停、停止按钮
    ImageButton play, stop;
    // 上一首，下一首按钮
    ImageButton pre, next;
    // 获取封面
    ImageView cover;

    ActivityReceiver activityReceiver;

    public static final String CTL_ACTION =
            "org.crazyit.action.CTL_ACTION";
    public static final String UPDATE_ACTION =
            "org.crazyit.action.UPDATE_ACTION";
    // 定义音乐的播放状态，0x11代表没有播放；0x12代表正在播放；0x13代表暂停
    int status = 0x11;
    String[] titleStrs = new String[] { "作曲家", "木桥小谣", "芒种" };
    String[] authorStrs = new String[] { "李荣浩", "王梓钰", "赵方婧" };
    Integer[] covers = new Integer[] { R.drawable.composer, R.drawable.bridge, R.drawable.graininear};

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

        // 获取程序界面界面中的两个按钮
        play = (ImageButton) this.findViewById(R.id.play);
        stop = (ImageButton) this.findViewById(R.id.stop);
        title = (TextView) findViewById(R.id.title);
        author = (TextView) findViewById(R.id.author);
        cover = findViewById(R.id.cover);
        pre = this.findViewById(R.id.pre);
        next = this.findViewById(R.id.next);

        // 为两个按钮的单击事件添加监听器
        play.setOnClickListener(this);
        stop.setOnClickListener(this);
        // 为上一首、下一首的单击事件添加监听器
        pre.setOnClickListener(this);
        next.setOnClickListener(this);

        activityReceiver = new ActivityReceiver();
        // 创建IntentFilter
        IntentFilter filter = new IntentFilter();
        // 指定BroadcastReceiver监听的Action
        filter.addAction(UPDATE_ACTION);
        // 注册BroadcastReceiver
        registerReceiver(activityReceiver, filter);

        Intent intent = new Intent(this, MusicService.class);
        // 启动后台Service
        startService(intent);
    }
    // 自定义的BroadcastReceiver，负责监听从Service传回来的广播
    public class ActivityReceiver extends BroadcastReceiver
    {
        @Override
        public void onReceive(Context context, Intent intent)
        {
            // 获取Intent中的update消息，update代表播放状态
            int update = intent.getIntExtra("update", -1);
            // 获取Intent中的current消息，current代表当前正在播放的歌曲
            int current = intent.getIntExtra("current", -1);
            if (current >= 0)
            {
                title.setText(titleStrs[current]);
                author.setText(authorStrs[current]);
                cover.setImageResource(covers[current]);
            }
            switch (update)
            {
                case 0x11:
                    play.setImageResource(R.drawable.play);
                    status = 0x11;
                    break;
                // 控制系统进入播放状态
                case 0x12:
                    // 播放状态下设置使用暂停图标
                    play.setImageResource(R.drawable.pause);
                    // 设置当前状态
                    status = 0x12;
                    break;
                // 控制系统进入暂停状态
                case 0x13:
                    // 暂停状态下设置使用播放图标
                    play.setImageResource(R.drawable.play);
                    // 设置当前状态
                    status = 0x13;
                    break;
            }
        }
    }
    @Override
    public void onClick(View source)
    {
        // 创建Intent
        Intent intent = new Intent("org.crazyit.action.CTL_ACTION");
        switch (source.getId())
        {
            // 按下播放/暂停按钮
            case R.id.play:
                intent.putExtra("control", 1);
                break;
            // 按下停止按钮
            case R.id.stop:
                intent.putExtra("control", 2);
                break;
            case R.id.pre:
                intent.putExtra("control",3);
            case R.id.next:
                intent.putExtra("control",4);
        }
        // 发送广播，将被Service组件中的BroadcastReceiver接收到
        sendBroadcast(intent);
    }
}