Android App 与 蓝牙服务 通信变更


首先，让我们来回顾下 Google官方 在 Android 5.0 引入的媒体应用框架：Android MediaSession框架简析。

然后，由于支持 蓝牙音乐 的音乐类App，也是基于 MediaBrowserService 实现的功能，所以音乐类App会根据 Android系统 的版本，进行客户端 MediaBrowser 连接服务端 MediaBrowserService 的初始化操作。

最后，若连接成功、获取到 MediaController，则下发相应的指令经 MediaBrowserService 转送到 蓝牙服务，控制音乐的切换、播放。

App 通过 MediaBrowserService 与 蓝牙服务 通信：

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1. Android P 及之前

实际是通过 BluetoothAvrcpController 接口的 sendPassThroughCmd() 方法，往 蓝牙服务 下发控制指令。

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mMediaBrowser = new MediaBrowserCompat(this,
                    new ComponentName("com.android.bluetooth",
                        "com.android.bluetooth.a2dpsink.mbs.A2dpMediaBrowserService"),
                    mConnectionCallback, null);
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/**
 * Implements the MediaBrowserService interface to AVRCP and A2DP
 *
 * This service provides a means for external applications to access A2DP and AVRCP.
 * The applications are expected to use MediaBrowser (see API) and all the music
 * browsing/playback/metadata can be controlled via MediaBrowser and MediaController.
 *
 * The current behavior of MediaSession exposed by this service is as follows:
 * 1. MediaSession is active (i.e. SystemUI and other overview UIs can see updates) when device is
 * connected and first starts playing. Before it starts playing we do not active the session.
 * 1.1 The session is active throughout the duration of connection.
 * 2. The session is de-activated when the device disconnects. It will be connected again when (1)
 * happens.
 */
public class A2dpMediaBrowserService extends MediaBrowserService {
    // 省略代码
}

2. Android Q 开始

A2dpMediaBrowserService 已被删除，使用 BluetoothMediaBrowserService 做替代。

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mMediaBrowser = new MediaBrowserCompat(this,
                    new ComponentName("com.android.bluetooth",
                        "com.android.bluetooth.avrcpcontroller.BluetoothMediaBrowserService"),
                    mConnectionCallback, null);
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/**
 * Implements the MediaBrowserService interface to AVRCP and A2DP
 *
 * This service provides a means for external applications to access A2DP and AVRCP.
 * The applications are expected to use MediaBrowser (see API) and all the music
 * browsing/playback/metadata can be controlled via MediaBrowser and MediaController.
 *
 * The current behavior of MediaSession exposed by this service is as follows:
 * 1. MediaSession is active (i.e. SystemUI and other overview UIs can see updates) when device is
 * connected and first starts playing. Before it starts playing we do not active the session.
 * 1.1 The session is active throughout the duration of connection.
 * 2. The session is de-activated when the device disconnects. It will be connected again when (1)
 * happens.
 */
public class BluetoothMediaBrowserService extends MediaBrowserService {
    // 省略代码
}

参考：

IVI 连接

蓝牙和NFC

蓝牙音乐之AVRCP在安卓系统中的实现