Android BLE （低功耗蓝牙）应用

Posted 2020-10-13 sovagxa&静默

蓝牙（ Bluetooth? ）：是一种无线技术标准，可实现固定设备、移动设备和楼宇个人域网之间的短距离数据交换（使用2.4—2.485GHz的ISM波段的UHF无线电波）。蓝牙技术最初由电信巨头爱立信公司于1994年创制，当时是作为RS232数据线的替代方案。蓝牙可连接多个设备，克服了数据同步的难题。

如今蓝牙由蓝牙技术联盟（Bluetooth Special Interest Group，简称SIG）管理。蓝牙技术联盟在全球拥有超过25,000家成员公司，它们分布在电信、计算机、网络、和消费电子等多重领域。IEEE将蓝牙技术列为IEEE 802.15.1，但如今已不再维持该标准。蓝牙技术联盟负责监督蓝牙规范的开发，管理认证项目，并维护商标权益。制造商的设备必须符合蓝牙技术联盟的标准才能以“蓝牙设备”的名义进入市场。蓝牙技术拥有一套专利网络，可发放给符合标准的设备。

 

一、蓝牙的分类

 

　　目前为止蓝牙分为两类：一是经典蓝牙（传统蓝牙），二是低功耗蓝牙（BLE）。顾名思义低功耗蓝牙功耗要比传统蓝牙低，所以广泛使用在智能穿戴设备上。要使安卓设备连接上智能穿戴设备（如智能手表），通过经典蓝牙的socket连接一般是连接不上的（为什么说一般呢，因为有些不良厂家和杂牌智能手环用的不是低功耗蓝牙，这个可以使用经典蓝牙连接上），必须要使用BLE的 GATT连接才能连接上。

二、GATT中的服务、特征值、描述、UUID

　　GATT连接涉及到四个比较陌生的名词：服务（service）、特征值（Characteristic）、描述（discript）、UUID，下面以智能手环为例分别来解释一下这些名词是什么意思。

• service：服务是包含了若干个数据包（特征值）的集合，一个智能设备可能包含多个服务，使用之恩那个设备生产厂商提供的UUID码来识别。比如之恩那个手环中有测心率的服务、步数的服务，心率和步数的数据包（特征值）都包含在服务中，通过指定的UUID来辨别到底是心率的服务还是步数的服务。
• characteristic：特征值包含在服务里面，顾名思义就是一种数据值，特征值包含一个或者多个描述。如心率是多少，今天走了多少步都可以放进特征值里面，服务中有多个特征值，也是通过UUID来识别
• discript：描述一般是对特征值的值进行描述，比如单位等等的描述，开发中一般用不到（我用不到）
• UUID：由蓝牙设备厂商提供的UUID，UUID是在硬件编程里已经确定了的，想要草所特定的服务、特征值都需要通过UUID来找。

三、安卓中GATT的操作

　　和经典蓝牙最开始一样，要检测蓝牙是否可用和蓝牙是否打开，这部分代码就不贴出来了。

　　一般操作GATT的教程都把操作放在安卓的server里面，具体原因还请大神指教。下面的server代码可以直接当作操作GATT的模板来使用，大部分都是些回调函数和对服务、特征值进行操作的方法：

public class UartService extends Service {
    private final static String TAG = UartService.class.getSimpleName();
    List<BluetoothGattService> serviceList = new ArrayList<BluetoothGattService>();//发现的服务列表

    private BluetoothAdapter mBluetoothAdapter;//本地蓝牙适配器
    private String mBluetoothDeviceAddress;//本地蓝牙MAC地址
    private BluetoothGatt mBluetoothGatt;//GTAA
    /**
     * 假设生产商提供了一个服务，该服务里面有两个特征值
     */
    private BluetoothGattService mBluetoothGattService;//gatt服务
    private BluetoothGattCharacteristic mBluetoothGattCharacteristic1;//gatt特征值1
    private BluetoothGattCharacteristic mBluetoothGattCharacteristic2;//gatt特征值2
    private int mConnectionState = STATE_DISCONNECTED;

    //连接状态常量
    private static final int STATE_DISCONNECTED = 0;
    private static final int STATE_CONNECTING = 1;
    private static final int STATE_CONNECTED = 2;

    //蓝牙厂商提供的UUID
    private static final UUID UUID_SERVICE = UUID.fromString("0000fff0-0000-1000-8000-00805f9b34fb"); //服务
    private static final UUID UUID_CHARA1 = UUID.fromString("0000fff1-0000-1000-8000-00805f9b34fb"); //特征值1
    private static final UUID UUID_CHARA2 = UUID.fromString("0000fff4-0000-1000-8000-00805f9b34fb"); //特征值2
    

    // Implements callback methods for GATT events that the app cares about.  For example,
    // connection change and services discovered.
    private final BluetoothGattCallback mGattCallback = new BluetoothGattCallback() {
        @Override
        public void onConnectionStateChange(BluetoothGatt gatt, int status, int newState) {
            if (newState == BluetoothProfile.STATE_CONNECTED) {
                mConnectionState = STATE_CONNECTED;
                Log.i(TAG, "Connected to GATT server.");
                // Attempts to discover services after successful connection.
                Log.i(TAG, "Attempting to start service discovery:" +
                        mBluetoothGatt.discoverServices());
            } else if (newState == BluetoothProfile.STATE_DISCONNECTED) {
                mConnectionState = STATE_DISCONNECTED;
                Log.i(TAG, "Disconnected from GATT server.");
            }
        }

        @Override
        public void onServicesDiscovered(BluetoothGatt gatt, int status) {//服务被发现
            if (status == BluetoothGatt.GATT_SUCCESS) {
                System.out.println("Service has bean discover.");
                mBluetoothGattService = gatt.getService(UUID_SERVICE);//发现服务
            } else {
                Log.w(TAG, "onServicesDiscovered received: " + status);
            }
        }

        @Override
        public void onCharacteristicRead(BluetoothGatt gatt,
                                         BluetoothGattCharacteristic characteristic,
                                         int status) {
            if (status == BluetoothGatt.GATT_SUCCESS) {
                Utiles.setData(characteristic);
            }
        }

        @Override
        public void onCharacteristicWrite(BluetoothGatt gatt,
                                          BluetoothGattCharacteristic characteristic,
                                          int status) {
        }

        @Override
        public void onCharacteristicChanged(BluetoothGatt gatt,
                                            BluetoothGattCharacteristic characteristic) {
        }
    };


    public class LocalBinder extends Binder {
        UartService getService() {
            return UartService.this;
        }
    }

    @Override
    public IBinder onBind(Intent intent) {
        return mBinder;
    }

    @Override
    public boolean onUnbind(Intent intent) {
        // After using a given device, you should make sure that BluetoothGatt.close() is called
        // such that resources are cleaned up properly.  In this particular example, close() is
        // invoked when the UI is disconnected from the Service.
        close();
        return super.onUnbind(intent);
    }

    private final IBinder mBinder = new LocalBinder();

    /**
     * Initializes a reference to the local Bluetooth adapter.
     *
     * @return Return true if the initialization is successful.
     */
    public boolean initialize() {//初始化
        // For API level 18 and above, get a reference to BluetoothAdapter through
        // BluetoothManager.
        mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
        if (mBluetoothAdapter == null) {
            Log.e(TAG, "Unable to obtain a BluetoothAdapter.");
            return false;
        }

        return true;
    }

    /**
     * Connects to the GATT server hosted on the Bluetooth LE device.
     *
     * @param address The device address of the destination device.
     *
     * @return Return true if the connection is initiated successfully. The connection result
     *         is reported asynchronously through the
     *         {@code BluetoothGattCallback#onConnectionStateChange(android.bluetooth.BluetoothGatt, int, int)}
     *         callback.
     */
    public boolean connect(final String address) {//连接服务
        if (mBluetoothAdapter == null || address == null) {
            Log.w(TAG, "BluetoothAdapter not initialized or unspecified address.");
            return false;
        }

        // Previously connected device.  Try to reconnect.
        if (mBluetoothDeviceAddress != null && address.equals(mBluetoothDeviceAddress)
                && mBluetoothGatt != null) {
            Log.d(TAG, "Trying to use an existing mBluetoothGatt for connection.");
            if (mBluetoothGatt.connect()) {
                mConnectionState = STATE_CONNECTING;
                return true;
            } else {
                return false;
            }
        }

        final BluetoothDevice device = mBluetoothAdapter.getRemoteDevice(address);
        if (device == null) {
            Log.w(TAG, "Device not found.  Unable to connect.");
            return false;
        }
        // We want to directly connect to the device, so we are setting the autoConnect
        // parameter to false.
        mBluetoothGatt = device.connectGatt(this, false, mGattCallback);
        Log.d(TAG, "Trying to create a new connection.");
        mBluetoothDeviceAddress = address;
        mConnectionState = STATE_CONNECTING;
        return true;
    }

    /**
     * Disconnects an existing connection or cancel a pending connection. The disconnection result
     * is reported asynchronously through the
     * {@code BluetoothGattCallback#onConnectionStateChange(android.bluetooth.BluetoothGatt, int, int)}
     * callback.
     */
    public void disconnect() {
        if (mBluetoothAdapter == null || mBluetoothGatt == null) {
            Log.w(TAG, "BluetoothAdapter not initialized");
            return;
        }
        mBluetoothGatt.disconnect();
    }

    /**
     * After using a given BLE device, the app must call this method to ensure resources are
     * released properly.
     */
    public void close() {
        if (mBluetoothGatt == null) {
            return;
        }
        mBluetoothGatt.close();
        mBluetoothGatt = null;
    }

    /**
     * Request a read on a given {@code BluetoothGattCharacteristic}. The read result is reported
     * asynchronously through the {@code BluetoothGattCallback#onCharacteristicRead(android.bluetooth.BluetoothGatt, android.bluetooth.BluetoothGattCharacteristic, int)}
     * callback.
     *
     * @param characteristic The characteristic to read from.
     */
    public void readCharacteristic(BluetoothGattCharacteristic characteristic) {
        if (mBluetoothAdapter == null || mBluetoothGatt == null) {
            Log.w(TAG, "BluetoothAdapter not initialized");
            return;
        }
        mBluetoothGatt.readCharacteristic(characteristic);
    }

    /**
     * Request a read on a given {@code BluetoothGattCharacteristic}. The read result is reported
     * asynchronously through the {@code BluetoothGattCallback#onCharacteristicRead(android.bluetooth.BluetoothGatt, android.bluetooth.BluetoothGattCharacteristic, int)}
     * callback.
     *
     * @param characteristic The characteristic to read from.
     */
    public void writeCharacteristic(BluetoothGattCharacteristic characteristic) {
        if (mBluetoothAdapter == null || mBluetoothGatt == null) {
            Log.w(TAG, "BluetoothAdapter not initialized");
            return;
        }
        mBluetoothGatt.writeCharacteristic(characteristic);
    }
    
    public boolean writeCharacteristic1Info(String s){
        if(mBluetoothGattService==null){
            return false;
        }
        mBluetoothGattCharacteristic1 = mBluetoothGattService.getCharacteristic(UUID_CHARA1);//获得特征值1
        mBluetoothGattCharacteristic1.setValue(s.getBytes());
        writeCharacteristic(mBluetoothGattCharacteristic1);
        return true;
    }

    /**
     * Enables or disables notification on a give characteristic.
     *
     * @param characteristic Characteristic to act on.
     * @param enabled If true, enable notification.  False otherwise.
     */
    public void setCharacteristicNotification(BluetoothGattCharacteristic characteristic,
                                              boolean enabled) {
        if (mBluetoothAdapter == null || mBluetoothGatt == null) {
            Log.w(TAG, "BluetoothAdapter not initialized");
            return;
        }
        mBluetoothGatt.setCharacteristicNotification(characteristic, enabled);
    }
    

    /**
     * Retrieves a list of supported GATT services on the connected device. This should be
     * invoked only after {@code BluetoothGatt#discoverServices()} completes successfully.
     *
     * @return A {@code List} of supported services.
     */
    public List<BluetoothGattService> getSupportedGattServices() {
        if (mBluetoothGatt == null) return null;

        return mBluetoothGatt.getServices();
    }
    
    @Override//使用startService启动服务时回调
    public int onStartCommand(Intent intent, int flags, int startId) {
        System.out.println("UartService Start");
        return super.onStartCommand(intent, flags, startId);
    }
}

 

ps：在发现服务后，最好把特征值取出来成一个列表，然后使用 setCharacteristicNotification(BluetoothGattCharacteristic characteristic,boolean enabled)方法对所有特征值进行设置，确保服务的特征值都可读可写。

 mBluetoothGattService = gatt.getService(UUID_SERVICE);//发现服务
 List<BluetoothGattCharacteristic> characteristics = mBluetoothGattService.getCharacteristics();
 if(characteristics.size()!=2){return;}//如果此服务不是有2个特征值，说明不是我们要的服务
 for (BluetoothGattCharacteristic bluetoothGattCharacteristic : characteristics) {
      setCharacteristicNotification(bluetoothGattCharacteristic, true);
 }
 mBluetoothGattCharacteristic1 = characteristics.get(0);
 mBluetoothGattCharacteristic2 = characteristics.get(1);

写完Service之后就可以用Service了

四、Service的使用

 

1. 在activity中绑定服务或者开启服务。绑定服务时，当activity销毁时服务跟着销毁；开启服务时，activity销毁，service不会跟着销毁
2. 初始化本地蓝牙设备

   mUartService.initialize();//初始化本地设备

    

3. 连接

   mUartService.connect(String MacAddress);//通过远程设备地址链接到远程设备

    

4. 链接后，回掉service中的onConnectionStateChange方法，其他的回掉方法也是字面意思，非常简单
5. 给设备发送数据

   writeCharacteristic1Info(String s);

    

---

 

总结 

 

1. 要使用service
2. 拿到服务之后马上设置特征值为可读可写，否则有可能导致收发数据不正常
3. UUID不一定是我的这个，是蓝牙厂商提供的，找硬件编程的小伙伴要UUID
4. 有什么问题望各位指教