低功耗藍牙包括的術語及概念：
如上圖所示，使用低功耗藍牙可以包括多個Profile，一個Profile中有多個Service，一個Service中有多個Characteristic，一個Characteristic中包括一個value和多個Descriptor。
Android中進行藍牙開發需要使用到的類的執行過程是：
1、使用BluetoothAdapter.startLeScan來掃描低功耗藍牙設備
2、在掃描到設備的回調函數中會得到BluetoothDevice對象，並使用BluetoothAdapter.stopLeScan停止掃描
3、使用BluetoothDevice.connectGatt來獲取到BluetoothGatt對象
4、執行BluetoothGatt.discoverServices，這個方法是異步操作，在回調函數onServicesDiscovered中得到status，通過判斷status是否等於BluetoothGatt.GATT_SUCCESS來判斷查找Service是否成功
5、如果成功了，則通過BluetoothGatt.getService來獲取BluetoothGattService
6、接着通過BluetoothGattService.getCharacteristic獲取BluetoothGattCharacteristic
7、然後通過BluetoothGattCharacteristic.getDescriptor獲取BluetoothGattDescriptor
Android Bluetooth源碼靜態類圖如下：
使用低功耗藍牙需要用到的權限：
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<uses-permission android:name="android.permission.BLUETOOTH"/><uses-permission android:name="android.permission.BLUETOOTH_ADMIN"/> |
下面介紹怎樣使用BLE:
1、準備BLE
1）獲取BluetoothAdapter
BluetoothAdapter是從系統服務獲取到的，全系統就一個。
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// Initializes Bluetooth adapter.final BluetoothManager bluetoothManager = (BluetoothManager) getSystemService(Context.BLUETOOTH_SERVICE);mBluetoothAdapter = bluetoothManager.getAdapter(); |
2）檢測藍牙是否打開
如果藍牙未打開，系統會自動打開，會彈出系統框展示打開藍牙。
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private BluetoothAdapter mBluetoothAdapter;...// Ensures Bluetooth is available on the device and it is enabled. If not,// displays a dialog requesting user permission to enable Bluetooth.if (mBluetoothAdapter == null || !mBluetoothAdapter.isEnabled()) { Intent enableBtIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE); startActivityForResult(enableBtIntent, REQUEST_ENABLE_BT);} |
2、查找BLE設備
因爲掃描BLE設備是電源密集型操作，浪費電量，因此要保證以下原則：
1）掃描到需要的設備後，馬上停止掃描；
2）給掃描一個時間限制
掃描示例代碼如下：
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/** * Activity for scanning and displaying available BLE devices. */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); } ... }...} |
如果只是要掃描到特定類型的設備，則使用接口 startLeScan(UUID[],
BluetoothAdapter.LeScanCallback)，通過UUID來查找設備。
掃描回調的代碼如下所示：
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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：我們既可以掃描BLE設備，也可以掃描普通藍牙設備，也可以同時將BLE設備和普通藍牙設備一起掃描到。
3、連接到GATT Server
獲取到BluetoothGatt實例，
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mBluetoothGatt = device.connectGatt(this, false, mGattCallback); |
具體實例如下：
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// A service that interacts with the BLE device via the 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); } } ... };...} |
其中，discoverService方式是異步的，它的回調方法是上面代碼中的onServiceDiscovered。
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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);} |
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// 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)); } }}; |
4、讀BLE屬性
一旦獲取到GATT的Services，就可以讀寫他們的屬性了，實例如下：
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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); } ... }...} |
在獲取Service的時候，每個藍牙設備都會有兩個默認的Service，它們和對應的UUID分別如下：
Bluetooth Generic Access Profile {00001800-0000-1000-8000-00805f9b34fb}
Bluetooth Generic Attribute Profile {00001801-0000-1000-8000-00805F9B34FB}
5、收到GATT通知
如果設備主動給手機發信息，則可以通過notification的方式，這種方式不用手機去輪詢地讀設備上的數據。手機可以用如下方式給設備設置notification功能。
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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); |
如果notificaiton方式對於某個Characteristic是enable的，那麼當設備上的這個Characteristic改變時，手機上的onCharacteristicChanged() 回調就會被促發。如下所示：
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@Override// Characteristic notificationpublic void onCharacteristicChanged(BluetoothGatt gatt, BluetoothGattCharacteristic characteristic) { broadcastUpdate(ACTION_DATA_AVAILABLE, characteristic);} |
6、關閉客戶端藍牙
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public void close() { if (mBluetoothGatt == null) { return; } mBluetoothGatt.close(); mBluetoothGatt = null;} |