蓝牙介绍

Android 4.3(API Level 18)介绍了内置平台支持蓝牙低能量的核心作用,并提供了API,应用程序可以用它来发现设备,查询服务，和读写字符。与传统的蓝牙相比，Bluetooth Low Energy (BLE) 旨在提供显著降低功耗。这使得Android应用能够与具有BLE的低耗能设备进行通信，例如，传感器、心率监视器,健身设备,等等。

BLE 权限
    为了在应用程序中使用蓝牙功能,必须声明蓝牙蓝牙许可。您需要这个权限执行任何蓝牙通信,如请求连接,接受连接,传输数据。 

    声明蓝牙权限需要在应用的manifest 文件中加如下代码：

<uses-permission android:name="android.permission.BLUETOOTH"/>
<uses-permission android:name="android.permission.BLUETOOTH_ADMIN"/>

 

如果你想声明应用程序仅BLE-capable设备可用,在你的应用程序的清单包括以下: 

<uses-feature android:name="android.hardware.bluetooth_le" android:required="true"/>

然而,如果你想让你的应用程序可用的设备不支持BLE,你应该还是这个元素包含在您的应用程序的清单,但在运行时设置android:required=“false”。在运行时您可以决定BLE可用性通过使用PackageManager.hasSystemFeature(): 

          //用这个检查设备是否支持BLE。
         if (!getPackageManager().hasSystemFeature(PackageManager.FEATURE_BLUETOOTH_LE)) {
                     Toast.makeText(this, R.string.ble_not_supported, Toast.LENGTH_SHORT).show();
                    finish();
                }

设置BLE
    BLE在您的应用程序可以交互之前,你需要确认在设备上是支持BLE,如果是这样,确保启用。注意这检查需要设置< uses-feature…/ >为false。

    如果不支持BLE,那么你应该禁用任何BLE特性。如果支持，但是已经禁用，你可以用你的应用启动它。完成这个设置需要两步，使用BluetoothAdapter。

1.获取luetoothAdapter。

    BluetoothAdapter代表设备的蓝牙适配器。整个系统有一个蓝牙适配器,和您的应用程序可以使用这个对象与它交互。下面的代码片段显示了如何获取适配器。使用getSystemService ()返回一个BluetoothManager实例,然后获取适配器。

Android 4.3(API LEVEL 18)引入了BluetoothManager:

//初始化蓝牙适配器
final BluetoothManager bluetoothManager =
        (BluetoothManager) getSystemService(Context.BLUETOOTH_SERVICE);
mBluetoothAdapter = bluetoothManager.getAdapter();

2.启动蓝牙

   接下来,您需要确保启用蓝牙。用isEnabled()检查蓝牙当前是否启动。如果这个方法返回false,那么蓝牙是关闭的。下面的代码片段检查是否启用蓝牙。如果没有,将提示用户去设置启用蓝牙。


if (mBluetoothAdapter == null || !mBluetoothAdapter.isEnabled()) {
    Intent enableBtIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
    startActivityForResult(enableBtIntent, REQUEST_ENABLE_BT);
}

 

搜索蓝牙设备

  搜索蓝牙设备使用startLeScan()方法。该方法以BluetoothAdapter.LeScanCallback作为参数,您必须实现这个回调,因为这是如何返回扫描结果。因为扫描非常耗电,你应该遵守如下规则：

· 只要找到了设备就应该停止搜索。

· 不要在一个无限循环中搜索, 需要设置一个时间限制搜索. 

 

下面代码作用是如何开始和结束搜索：

 

 


public class DeviceScanActivity extends ListActivity {

    private BluetoothAdapter mBluetoothAdapter;
    private boolean mScanning;
    private Handler mHandler;

    // Stops scanning after 10 seconds.
    private static final long SCAN_PERIOD = 10000;
    ...
    private void scanLeDevice(final boolean enable) {
        if (enable) {
            // Stops scanning after a pre-defined scan period.
            mHandler.postDelayed(new Runnable() {
                @Override
                public void run() {
                    mScanning = false;
                    mBluetoothAdapter.stopLeScan(mLeScanCallback);
                }
            }, SCAN_PERIOD);

            mScanning = true;
            mBluetoothAdapter.startLeScan(mLeScanCallback);
        } else {
            mScanning = false;
            mBluetoothAdapter.stopLeScan(mLeScanCallback);
        }
        ...
    }
...
}

    如果你想只扫描特定类型的外围设备,你可以使用startLeScan(UUID[],BluetoothAdapter.LeScanCallback),提供一个UUID对象数组,指定蓝牙服务应用程序所支持的。 

    这里使用BluetoothAdapter.LeScanCallback的实现用来显示蓝牙扫描结果:

private LeDeviceListAdapter mLeDeviceListAdapter;
...
// Device scan callback.
private BluetoothAdapter.LeScanCallback mLeScanCallback =
        new BluetoothAdapter.LeScanCallback() {
    @Override
    public void onLeScan(final BluetoothDevice device, int rssi,
            byte[] scanRecord) {
        runOnUiThread(new Runnable() {
           @Override
           public void run() {
               mLeDeviceListAdapter.addDevice(device);
               mLeDeviceListAdapter.notifyDataSetChanged();
           }
       });
   }
};

注意：不能在同一时间扫描BLE和传统的蓝牙。

链接 GATT Server
      与BLE设备交互的第一步是连接到它,更具体地说,连接到设备上的GATT服务器。连接到GATT服务器使用connectGatt()方法,这个方法取三个参数:一个上下文对象,(布尔指示是否自动连接到设备就可用),和BluetoothGattCallback回调函数。

mBluetoothGatt = device.connectGatt(this, false, mGattCallback);

    这个连接到GATT服务端通过BLE设备,并返回一个BluetoothGatt实例,然后您可以使用GATT客户端进行操作。调用者(Android应用程序)是GATT客户端。BluetoothGattCallback用于提供结果给客户端,如连接状态,以及任何进一步的GATT客户端操作。

     在这个例子中,有幸获得应用程序提供了一个活动(DeviceControlActivity)连接,显示数据,并显示GATT服务和支持的设备特征。基于用户输入,此活动与一个服务交互称为BluetoothLeService,这服务与BLE设备交互是通过Android BLE API:

public class BluetoothLeService extends Service {
    private final static String TAG = BluetoothLeService.class.getSimpleName();

    private BluetoothManager mBluetoothManager;
    private BluetoothAdapter mBluetoothAdapter;
    private String mBluetoothDeviceAddress;
    private BluetoothGatt mBluetoothGatt;
    private int mConnectionState = STATE_DISCONNECTED;

    private static final int STATE_DISCONNECTED = 0;
    private static final int STATE_CONNECTING = 1;
    private static final int STATE_CONNECTED = 2;

    public final static String ACTION_GATT_CONNECTED =
            "com.example.bluetooth.le.ACTION_GATT_CONNECTED";
    public final static String ACTION_GATT_DISCONNECTED =
            "com.example.bluetooth.le.ACTION_GATT_DISCONNECTED";
    public final static String ACTION_GATT_SERVICES_DISCOVERED =
            "com.example.bluetooth.le.ACTION_GATT_SERVICES_DISCOVERED";
    public final static String ACTION_DATA_AVAILABLE =
            "com.example.bluetooth.le.ACTION_DATA_AVAILABLE";
    public final static String EXTRA_DATA =
            "com.example.bluetooth.le.EXTRA_DATA";

    public final static UUID UUID_HEART_RATE_MEASUREMENT =
            UUID.fromString(SampleGattAttributes.HEART_RATE_MEASUREMENT);

    // Various callback methods defined by the BLE API.
    private final BluetoothGattCallback mGattCallback =
            new BluetoothGattCallback() {
        @Override
        public void onConnectionStateChange(BluetoothGatt gatt, int status,
                int newState) {
            String intentAction;
            if (newState == BluetoothProfile.STATE_CONNECTED) {
                intentAction = ACTION_GATT_CONNECTED;
                mConnectionState = STATE_CONNECTED;
                broadcastUpdate(intentAction);
                Log.i(TAG, "Connected to GATT server.");
                Log.i(TAG, "Attempting to start service discovery:" +
                        mBluetoothGatt.discoverServices());

            } else if (newState == BluetoothProfile.STATE_DISCONNECTED) {
                intentAction = ACTION_GATT_DISCONNECTED;
                mConnectionState = STATE_DISCONNECTED;
                Log.i(TAG, "Disconnected from GATT server.");
                broadcastUpdate(intentAction);
            }
        }

        @Override
        // New services discovered
        public void onServicesDiscovered(BluetoothGatt gatt, int status) {
            if (status == BluetoothGatt.GATT_SUCCESS) {
                broadcastUpdate(ACTION_GATT_SERVICES_DISCOVERED);
            } else {
                Log.w(TAG, "onServicesDiscovered received: " + status);
            }
        }

        @Override
        // Result of a characteristic read operation
        public void onCharacteristicRead(BluetoothGatt gatt,
                BluetoothGattCharacteristic characteristic,
                int status) {
            if (status == BluetoothGatt.GATT_SUCCESS) {
                broadcastUpdate(ACTION_DATA_AVAILABLE, characteristic);
            }
        }
     ...
    };
...
}

 

 

    当一个特定的回调函数被触发，它调用适当的broadcastUpdate()辅助方法并将其传递一个action。注意,本节中的数据解析执行按照蓝牙心率测量概要文件规范:

private void broadcastUpdate(final String action) {
    final Intent intent = new Intent(action);
    sendBroadcast(intent);
}

private void broadcastUpdate(final String action,
                             final BluetoothGattCharacteristic characteristic) {
    final Intent intent = new Intent(action);

    // This is special handling for the Heart Rate Measurement profile. Data
    // parsing is carried out as per profile specifications.
    if (UUID_HEART_RATE_MEASUREMENT.equals(characteristic.getUuid())) {
        int flag = characteristic.getProperties();
        int format = -1;
        if ((flag & 0x01) != 0) {
            format = BluetoothGattCharacteristic.FORMAT_UINT16;
            Log.d(TAG, "Heart rate format UINT16.");
        } else {
            format = BluetoothGattCharacteristic.FORMAT_UINT8;
            Log.d(TAG, "Heart rate format UINT8.");
        }
        final int heartRate = characteristic.getIntValue(format, 1);
        Log.d(TAG, String.format("Received heart rate: %d", heartRate));
        intent.putExtra(EXTRA_DATA, String.valueOf(heartRate));
    } else {
        // For all other profiles, writes the data formatted in HEX.
        final byte[] data = characteristic.getValue();
        if (data != null && data.length > 0) {
            final StringBuilder stringBuilder = new StringBuilder(data.length);
            for(byte byteChar : data)
                stringBuilder.append(String.format("%02X ", byteChar));
            intent.putExtra(EXTRA_DATA, new String(data) + "\n" +
                    stringBuilder.toString());
        }
    }
    sendBroadcast(intent);
}

Back in DeviceControlActivity, these events are handled by a BroadcastReceiver:

// Handles various events fired by the Service.
// ACTION_GATT_CONNECTED: connected to a GATT server.
// ACTION_GATT_DISCONNECTED: disconnected from a GATT server.
// ACTION_GATT_SERVICES_DISCOVERED: discovered GATT services.
// ACTION_DATA_AVAILABLE: received data from the device. This can be a
// result of read or notification operations.
private final BroadcastReceiver mGattUpdateReceiver = new BroadcastReceiver() {
    @Override
    public void onReceive(Context context, Intent intent) {
        final String action = intent.getAction();
        if (BluetoothLeService.ACTION_GATT_CONNECTED.equals(action)) {
            mConnected = true;
            updateConnectionState(R.string.connected);
            invalidateOptionsMenu();
        } else if (BluetoothLeService.ACTION_GATT_DISCONNECTED.equals(action)) {
            mConnected = false;
            updateConnectionState(R.string.disconnected);
            invalidateOptionsMenu();
            clearUI();
        } else if (BluetoothLeService.
                ACTION_GATT_SERVICES_DISCOVERED.equals(action)) {
            // Show all the supported services and characteristics on the
            // user interface.
            displayGattServices(mBluetoothLeService.getSupportedGattServices());
        } else if (BluetoothLeService.ACTION_DATA_AVAILABLE.equals(action)) {
            displayData(intent.getStringExtra(BluetoothLeService.EXTRA_DATA));
        }
    }
};

 

阅读BLE属性 

    一旦你的Android应用程序连接到一个GATT服务器和发现服务,它可以读取和写入属性。例如,这段代码遍历服务器的服务和数据并将它们显示在UI中:

public class DeviceControlActivity extends Activity {
    ...
    // Demonstrates how to iterate through the supported GATT
    // Services/Characteristics.
    // In this sample, we populate the data structure that is bound to the
    // ExpandableListView on the UI.
    private void displayGattServices(List<BluetoothGattService> gattServices) {
        if (gattServices == null) return;
        String uuid = null;
        String unknownServiceString = getResources().
                getString(R.string.unknown_service);
        String unknownCharaString = getResources().
                getString(R.string.unknown_characteristic);
        ArrayList<HashMap<String, String>> gattServiceData =
                new ArrayList<HashMap<String, String>>();
        ArrayList<ArrayList<HashMap<String, String>>> gattCharacteristicData
                = new ArrayList<ArrayList<HashMap<String, String>>>();
        mGattCharacteristics =
                new ArrayList<ArrayList<BluetoothGattCharacteristic>>();

        // Loops through available GATT Services.
        for (BluetoothGattService gattService : gattServices) {
            HashMap<String, String> currentServiceData =
                    new HashMap<String, String>();
            uuid = gattService.getUuid().toString();
            currentServiceData.put(
                    LIST_NAME, SampleGattAttributes.
                            lookup(uuid, unknownServiceString));
            currentServiceData.put(LIST_UUID, uuid);
            gattServiceData.add(currentServiceData);

            ArrayList<HashMap<String, String>> gattCharacteristicGroupData =
                    new ArrayList<HashMap<String, String>>();
            List<BluetoothGattCharacteristic> gattCharacteristics =
                    gattService.getCharacteristics();
            ArrayList<BluetoothGattCharacteristic> charas =
                    new ArrayList<BluetoothGattCharacteristic>();
           // Loops through available Characteristics.
            for (BluetoothGattCharacteristic gattCharacteristic :
                    gattCharacteristics) {
                charas.add(gattCharacteristic);
                HashMap<String, String> currentCharaData =
                        new HashMap<String, String>();
                uuid = gattCharacteristic.getUuid().toString();
                currentCharaData.put(
                        LIST_NAME, SampleGattAttributes.lookup(uuid,
                                unknownCharaString));
                currentCharaData.put(LIST_UUID, uuid);
                gattCharacteristicGroupData.add(currentCharaData);
            }
            mGattCharacteristics.add(charas);
            gattCharacteristicData.add(gattCharacteristicGroupData);
         }
    ...
    }
...
}

接收GATT通知
   当一个特定的设备上的特征变化需要BLE的应用通知。这个代码片段显示了如何设置一个通知特性,使用setCharacteristicNotification()方法:

 

 

private BluetoothGatt mBluetoothGatt;
BluetoothGattCharacteristic characteristic;
boolean enabled;
...
mBluetoothGatt.setCharacteristicNotification(characteristic, enabled);
...
BluetoothGattDescriptor descriptor = characteristic.getDescriptor(
        UUID.fromString(SampleGattAttributes.CLIENT_CHARACTERISTIC_CONFIG));
descriptor.setValue(BluetoothGattDescriptor.ENABLE_NOTIFICATION_VALUE);
mBluetoothGatt.writeDescriptor(descriptor);

     一旦通知作为一个特性被启用,如果远程设备上的特性变化将触发onCharacteristicChanged()回调。

 

@Override
// Characteristic notification
public void onCharacteristicChanged(BluetoothGatt gatt,
        BluetoothGattCharacteristic characteristic) {
    broadcastUpdate(ACTION_DATA_AVAILABLE, characteristic);
}

关闭客户端应用
 

    一旦应用程序完成使用BLE设备，应该调用close()方法去释放系统资源。

public void close() {
    if (mBluetoothGatt == null) {
        return;
    }
    mBluetoothGatt.close();
    mBluetoothGatt = null;
}