藍牙介紹

Android 4.3(API Level 18)介紹了內置平臺支持藍牙低能量的核心做用,並提供了API,應用程序能夠用它來發現設備,查詢服務，和讀寫字符。與傳統的藍牙相比，Bluetooth Low Energy (BLE) 旨在提供顯著下降功耗。這使得Android應用可以與具備BLE的低耗能設備進行通訊，例如，傳感器、心率監視器,健身設備,等等。

BLE 權限
    爲了在應用程序中使用藍牙功能,必須聲明藍牙藍牙許可。您須要這個權限執行任何藍牙通訊,如請求鏈接,接受鏈接,傳輸數據。 

    聲明藍牙權限須要在應用的manifest 文件中加以下代碼：

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

 

若是你想聲明應用程序僅BLE-capable設備可用,在你的應用程序的清單包括如下: 

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

然而,若是你想讓你的應用程序可用的設備不支持BLE,你應該仍是這個元素包含在您的應用程序的清單,但在運行時設置android:required=「false」。在運行時您能夠決定BLE可用性經過使用PackageManager.hasSystemFeature(): 

          //用這個檢查設備是否支持BLE。
         if (!getPackageManager().hasSystemFeature(PackageManager.FEATURE_BLUETOOTH_LE)) {
                     Toast.makeText(this, R.string.ble_not_supported, Toast.LENGTH_SHORT).show();
                    finish();
                }

設置BLE
    BLE在您的應用程序能夠交互以前,你須要確認在設備上是支持BLE,若是是這樣,確保啓用。注意這檢查須要設置< uses-feature…/ >爲false。

    若是不支持BLE,那麼你應該禁用任何BLE特性。若是支持，可是已經禁用，你能夠用你的應用啓動它。完成這個設置須要兩步，使用BluetoothAdapter。

1.獲取luetoothAdapter。

    BluetoothAdapter表明設備的藍牙適配器。整個系統有一個藍牙適配器,和您的應用程序可使用這個對象與它交互。下面的代碼片斷顯示瞭如何獲取適配器。使用getSystemService ()返回一個BluetoothManager實例,而後獲取適配器。

Android 4.3(API LEVEL 18)引入了BluetoothManager:

//初始化藍牙適配器
final BluetoothManager bluetoothManager =
        (BluetoothManager) getSystemService(Context.BLUETOOTH_SERVICE);
mBluetoothAdapter = bluetoothManager.getAdapter();

2.啓動藍牙

   接下來,您須要確保啓用藍牙。用isEnabled()檢查藍牙當前是否啓動。若是這個方法返回false,那麼藍牙是關閉的。下面的代碼片斷檢查是否啓用藍牙。若是沒有,將提示用戶去設置啓用藍牙。


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

 

搜索藍牙設備

  搜索藍牙設備使用startLeScan()方法。該方法以BluetoothAdapter.LeScanCallback做爲參數,您必須實現這個回調,由於這是如何返回掃描結果。由於掃描很是耗電,你應該遵照以下規則：

· 只要找到了設備就應該中止搜索。

· 不要在一個無限循環中搜索, 須要設置一個時間限制搜索. 

 

下面代碼做用是如何開始和結束搜索：

 

 


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);
        }
        ...
    }
...
}

    若是你想只掃描特定類型的外圍設備,你可使用startLeScan(UUID[],BluetoothAdapter.LeScanCallback),提供一個UUID對象數組,指定藍牙服務應用程序所支持的。 

    這裏使用BluetoothAdapter.LeScanCallback的實現用來顯示藍牙掃描結果:

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：不能在同一時間掃描BLE和傳統的藍牙。

連接 GATT Server
      與BLE設備交互的第一步是鏈接到它,更具體地說,鏈接到設備上的GATT服務器。鏈接到GATT服務器使用connectGatt()方法,這個方法取三個參數:一個上下文對象,(布爾指示是否自動鏈接到設備就可用),和BluetoothGattCallback回調函數。

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

    這個鏈接到GATT服務端經過BLE設備,並返回一個BluetoothGatt實例,而後您可使用GATT客戶端進行操做。調用者(Android應用程序)是GATT客戶端。BluetoothGattCallback用於提供結果給客戶端,如鏈接狀態,以及任何進一步的GATT客戶端操做。

     在這個例子中,有幸得到應用程序提供了一個活動(DeviceControlActivity)鏈接,顯示數據,並顯示GATT服務和支持的設備特徵。基於用戶輸入,此活動與一個服務交互稱爲BluetoothLeService,這服務與BLE設備交互是經過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);
            }
        }
     ...
    };
...
}

 

 

    當一個特定的回調函數被觸發，它調用適當的broadcastUpdate()輔助方法並將其傳遞一個action。注意,本節中的數據解析執行按照藍牙心率測量概要文件規範:

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));
        }
    }
};

 

閱讀BLE屬性 

    一旦你的Android應用程序鏈接到一個GATT服務器和發現服務,它能夠讀取和寫入屬性。例如,這段代碼遍歷服務器的服務和數據並將它們顯示在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
   當一個特定的設備上的特徵變化須要BLE的應用通知。這個代碼片斷顯示瞭如何設置一個通知特性,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);

     一旦通知做爲一個特性被啓用,若是遠程設備上的特性變化將觸發onCharacteristicChanged()回調。

 

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

關閉客戶端應用
 

    一旦應用程序完成使用BLE設備，應該調用close()方法去釋放系統資源。

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