蓝牙开发 基础知识

零、基础知识

0.1、Android 应用可通过 Bluetooth API 执行以下操作

• 扫描其他蓝牙设备
• 查询本地蓝牙适配器的配对蓝牙设备
• 建立 RFCOMM 通道
• 通过服务发现连接到其他设备
• 与其他设备进行双向数据传输
• 管理多个连接

0.2、蓝牙进行通信的四大必需任务

1. 设置蓝牙
2. 查找局部区域内的配对设备或可用设备
3. 连接设备
4. 在设备之间传输数据

0.3、动作

请求连接、接受连接和传输数据

蓝牙协议是适用于设备间蓝牙通信的无线接口规范。
如果手机要与无线耳机进行连接，则两台设备都必须支持免提蓝牙协议。

0.4、协议

• HFP协议：Android 提供 BluetoothHeadset 类，该类是用于控制蓝牙耳机服务的代理。其中包括蓝牙耳机和免提 (v1.5) 的协议。BluetoothHeadset 类包含对 AT 命令的支持。
• A2DP协议：定义如何通过蓝牙连接和流式传输，将高质量音频从一个设备传输至另一个设备。Android 提供 BluetoothA2dp 类，该类是用于控制蓝牙 A2DP 服务的代理。
• 蓝牙健康设备 (HDP)协议：该协议允许您创建应用，从而与支持蓝牙功能的健康设备（例如心率监测仪、血糖仪、温度计、台秤等）进行通信。

0.5、名词

1. RFCOMM 通道
2. AT 命令
3. 耳机协议
4. BluetoothHeadset类
5. BluetoothSocket类
6. SDP lookup of uuid
7. SDP record

供应商特定的 AT 命令
从 Android 3.0（API 级别 11）开始，应用可注册接收耳机发送的预定义供应商特定 AT 命令（例如 Plantronics +XEVENT 命令）的系统广播。例如，应用可接收指示所连接设备电池电量的广播，并根据需要通知用户或采取其他操作。为 ACTION_VENDOR_SPECIFIC_HEADSET_EVENT Intent 创建广播接收器，以处理耳机的供应商特定 AT 命令。

一、使用蓝牙

1.1 设置蓝牙

启用蓝牙：
获取 BluetoothAdapter。
所有蓝牙 Activity 都需要 BluetoothAdapter。如要获取 BluetoothAdapter，请调用静态的 getDefaultAdapter() 方法。此方法会返回一个 BluetoothAdapter 对象，表示设备自身的蓝牙适配器（蓝牙无线装置）。整个系统只有一个蓝牙适配器，并且您的应用可使用此对象与之进行交互。如果 getDefaultAdapter() 返回 null，则表示设备不支持蓝牙。

BluetoothAdapter bluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
if (bluetoothAdapter == null) {// Device doesn't support Bluetooth
} else {if (!bluetoothAdapter.isEnabled()) {Intent enableBtIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);startActivityForResult(enableBtIntent, REQUEST_ENABLE_BT);}
}

如果成功启用蓝牙，您的 Activity 会在 onActivityResult() 回调中收到 RESULT_OK 结果代码。如果由于某个错误（或用户响应“No”）未成功启用蓝牙，则结果代码为 RESULT_CANCELED。

1.2 查找设备

1.2.1 设备发现

如要开始发现设备，只需调用 startDiscovery()。该进程为异步操作，并且会返回一个布尔值，指示发现进程是否已成功启动。发现进程通常包含约 12 秒钟的查询扫描，随后会对发现的每台设备进行页面扫描，以检索其蓝牙名称。

@Override
protected void onCreate(Bundle savedInstanceState) {...// Register for broadcasts when a device is discovered.IntentFilter filter = new IntentFilter(BluetoothDevice.ACTION_FOUND);registerReceiver(receiver, filter);
}// Create a BroadcastReceiver for ACTION_FOUND.
private final BroadcastReceiver receiver = new BroadcastReceiver() {public void onReceive(Context context, Intent intent) {String action = intent.getAction();if (BluetoothDevice.ACTION_FOUND.equals(action)) {// Discovery has found a device. Get the BluetoothDevice// object and its info from the Intent.BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);String deviceName = device.getName();String deviceHardwareAddress = device.getAddress(); // MAC address}}
};@Override
protected void onDestroy() {super.onDestroy();...// Don't forget to unregister the ACTION_FOUND receiver.unregisterReceiver(receiver);
}

1.2.2 查询配对设备的列表

Set<BluetoothDevice> pairedDevices = bluetoothAdapter.getBondedDevices();if (pairedDevices.size() > 0) {// There are paired devices. Get the name and address of each paired device.for (BluetoothDevice device : pairedDevices) {String deviceName = device.getName();String deviceHardwareAddress = device.getAddress(); // MAC address}
}

1.2.3 启用可检测性

Intent discoverableIntent =new Intent(BluetoothAdapter.ACTION_REQUEST_DISCOVERABLE);
discoverableIntent.putExtra(BluetoothAdapter.EXTRA_DISCOVERABLE_DURATION, 300); // 可检测性开启300秒
startActivity(discoverableIntent);

注意：如果尚未在设备上启用蓝牙，则启用设备可检测性会自动启用蓝牙。

1.2.4 已配对与已连接的区别

已配对是指两台设备知晓彼此的存在，具有可用于身份验证的共享链路密钥，并且能够与彼此建立加密连接。
已连接是指设备当前共享一个 RFCOMM 通道，并且能够向彼此传输数据。当前的 Android Bluetooth API 要求规定，只有先对设备进行配对，然后才能建立 RFCOMM 连接。在使用 Bluetooth API 发起加密连接时，系统会自动执行配对。

二、连接设备

2.1. 连接技术

2.1.1 作为服务器连接

private class AcceptThread extends Thread {private final BluetoothServerSocket mmServerSocket;public AcceptThread() {// Use a temporary object that is later assigned to mmServerSocket// because mmServerSocket is final.BluetoothServerSocket tmp = null;try {// MY_UUID is the app's UUID string, also used by the client code.tmp = bluetoothAdapter.listenUsingRfcommWithServiceRecord(NAME, MY_UUID);} catch (IOException e) {Log.e(TAG, "Socket's listen() method failed", e);}mmServerSocket = tmp;}public void run() {BluetoothSocket socket = null;// Keep listening until exception occurs or a socket is returned.while (true) {try {socket = mmServerSocket.accept();} catch (IOException e) {Log.e(TAG, "Socket's accept() method failed", e);break;}if (socket != null) {// A connection was accepted. Perform work associated with// the connection in a separate thread.manageMyConnectedSocket(socket);mmServerSocket.close();break;}}}// Closes the connect socket and causes the thread to finish.public void cancel() {try {mmServerSocket.close();} catch (IOException e) {Log.e(TAG, "Could not close the connect socket", e);}}
}

2.1.2 作为客户端连接

private class ConnectThread extends Thread {private final BluetoothSocket mmSocket;private final BluetoothDevice mmDevice;public ConnectThread(BluetoothDevice device) {// Use a temporary object that is later assigned to mmSocket// because mmSocket is final.BluetoothSocket tmp = null;mmDevice = device;try {// Get a BluetoothSocket to connect with the given BluetoothDevice.// MY_UUID is the app's UUID string, also used in the server code.tmp = device.createRfcommSocketToServiceRecord(MY_UUID);} catch (IOException e) {Log.e(TAG, "Socket's create() method failed", e);}mmSocket = tmp;}public void run() {// Cancel discovery because it otherwise slows down the connection.bluetoothAdapter.cancelDiscovery();try {// Connect to the remote device through the socket. This call blocks// until it succeeds or throws an exception.mmSocket.connect();} catch (IOException connectException) {// Unable to connect; close the socket and return.try {mmSocket.close();} catch (IOException closeException) {Log.e(TAG, "Could not close the client socket", closeException);}return;}// The connection attempt succeeded. Perform work associated with// the connection in a separate thread.manageMyConnectedSocket(mmSocket);}// Closes the client socket and causes the thread to finish.public void cancel() {try {mmSocket.close();} catch (IOException e) {Log.e(TAG, "Could not close the client socket", e);}}
}