Functional Requirements

 利用BroadcastReceiver组件实现基本音乐播放器功能：上一曲下一曲切换、
 播放、暂停，以及当前播放歌曲信息显示

achieve

1. Static Registration

(1) The broadcast will not end with the end of the Activity's life cycle, it always exists, even if the application is closed, it will be awakened to accept the broadcast
(2) global broadcast

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

    <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>

2. Send and receive (main code)

Create an Intent
Call the sendBroadcast () function to broadcast the message carried by the Intent

activity_main.xml

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

    <ImageButton
        android:id="@+id/previous"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:src="@android:drawable/ic_media_previous" />

    <ImageButton
        android:id="@+id/play"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:src="@android:drawable/ic_media_play" />

    <ImageButton
        android:id="@+id/stop"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:src="@android:drawable/ic_media_pause" />

    <ImageButton
        android:id="@+id/next"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:src="@android:drawable/ic_media_next" />

    <LinearLayout
        android:orientation="vertical"
        android:layout_width="match_parent"
        android:layout_height="match_parent">
        <TextView
            android:id="@+id/title"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:textSize="20dp"
            android:textColor="#000000"
            android:ellipsize="marquee"
            android:layout_weight="1"
            android:marqueeRepeatLimit="marquee_forever"/>
        <TextView
            android:id="@+id/author"
            android:textSize="12dp"
            android:gravity="center_vertical"
            android:layout_weight="1"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"/>
    </LinearLayout>

MainActivity.java

    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;
            //按下上一首按钮
            case R.id.previous:
                intent.putExtra("control",3);
                break;
            //按下下一首按钮
            case R.id.next:
                intent.putExtra("control",4);
                break;
        }
        //发送广播，将被Service组件中的BroadcastReceiver接收到
        sendBroadcast(intent);
    }

    //自定义的BroadcastReceiver，负责监听从Service传回的广播
    private 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]);
            }
            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.mic);
                    //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;
            }
        }
    }

MusicService.java

    public class MyReceiver extends BroadcastReceiver
    {
        @Override
        public void onReceive(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;
                    }
                    break;
                case 3:
                    //原来处于没有播放或暂停状态
                    if (status==0x11||status==0x13)
                    {
                        if(current==0) {
                            current=2;
                            prepareAndPlay(musics[current]);
                        }
                        //准备并播放音乐
                        else {
                            current=current-1;
                            prepareAndPlay(musics[current]);
                        }
                        status=0x12;
                    }
                    //原来处于播放状态
                    else if (status==0x12)
                    {
                        //上一首//准备并播放音乐
                        if(current==0) {
                            current=2;
                            prepareAndPlay(musics[current]);
                        }
                        else {
                            current=current-1;
                            prepareAndPlay(musics[current]);
                        }
                    }
                    break;
                case 4:
                    //原来处于没有播放或暂停状态
                    if (status==0x11||status==0x13)
                    {
                        if(current==2) {
                            current=0;
                            prepareAndPlay(musics[current]);
                        }   //准备并播放音乐
                        else {
                            current=current+1;
                            prepareAndPlay(musics[current]);
                        }
                        status=0x12;
                    }
                    //原来处于播放状态
                    else if (status==0x12)
                    {
                        //下一首
                        if(current==2) {
                            current=0;
                            prepareAndPlay(musics[current]);
                        }
                        else {
                            current=current+1;
                            prepareAndPlay(musics[current]);
                        }
                    }
                    break;
            }
            //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
            sendBroadcast(sendIntent);
        }
    }