BLE 即 Bluetooth Low Energy，藍(lán)牙低功耗技術(shù)驼仪，是藍(lán)牙4.0引入的新技術(shù)∷胰澹現(xiàn)在越來越多的智能設(shè)備使用了BLE，像滿大街的智能手環(huán)涮俄。
　　Android在4.3（API 18）中引進(jìn)了對BLE central role的支持蛉拙，同時提供API供App來掃描設(shè)備关斜、查詢服務(wù)屿附、讀寫特征值等舌镶。

關(guān)鍵術(shù)語和概念

• Generic Attribute Profile (GATT)—GATT概述（profile）是一個通用的通過BLE連接來發(fā)送和接受短的被稱為“屬性”的數(shù)據(jù)的規(guī)范跋涣。所有現(xiàn)在的低功耗應(yīng)用概述（profile）都基于GATT。

• 藍(lán)牙標(biāo)準(zhǔn)協(xié)會為低功耗設(shè)備定義了很多 profiles敛瓷。概述（profile）是設(shè)備在特定應(yīng)用場景下如何工作的規(guī)范。注意設(shè)備能實(shí)現(xiàn)不止一種概述，例如野来，一個設(shè)備可以包含心律監(jiān)測和電池電量檢測。

• Attribute Protocol (ATT)—GATT建立在屬性協(xié)議（ATT）上踪旷。通常他們一起被叫做GATT/ATT曼氛。ATT針對在BLE設(shè)備上運(yùn)行做了優(yōu)化。為了這個目的令野，它使用盡可能少的字節(jié)舀患。每個屬性通過一個標(biāo)準(zhǔn)的128位格式的字符串ID作為唯一標(biāo)識信息的通用唯一識別碼（Universally Unique Identifier 即UUID）來唯一的標(biāo)識。屬性被ATT格式化為特征和服務(wù)來傳輸气破。

• Characteristic—一個特征包含一個單一的值（value）和0-n個描述信息塊（descriptor）來描述特征的值聊浅。特征可以被認(rèn)為是一種類型（type），類似一個類（class）现使。

• Descriptor—描述信息塊定義了特征值（characteristic value）的屬性低匙，一個描述信息塊可能指定一個可讀的描述，一個特征值可接受的范圍碳锈，或者指定一個特征值的計(jì)量單位顽冶。

• Service—服務(wù)是特征的集合。例如售碳，你可以有個叫做“心率檢測器”且包含“心律測量方式”特征的服務(wù)强重。你可以在bluetooth.org上找到一份現(xiàn)有的基于GATT的概述（profile）和服務(wù)列表绞呈。

角色和職責(zé)

• 中心 vs. 外圍。你必須同時有這兩種設(shè)備才能建立他們之間的連接间景。兩個中心設(shè)備或者兩個外圍設(shè)備都不能建立連接佃声。

• GATT服務(wù)端 vs. GATT客戶端。這取決于他們之間是怎么交流的拱燃。

BLE權(quán)限

<uses-permission android:name="android.permission.BLUETOOTH"/>
<!--下面的用來掃描設(shè)備和修改設(shè)置秉溉，用了這個必須同時用上面那個-->
<uses-permission android:name="android.permission.BLUETOOTH_ADMIN"/>

檢查設(shè)備是否支持BLE：

// Use this check to determine whether BLE is supported on the device. Then
// you can selectively disable BLE-related features.
if (!getPackageManager().hasSystemFeature(PackageManager.FEATURE_BLUETOOTH_LE)) {
    Toast.makeText(this, R.string.ble_not_supported, Toast.LENGTH_SHORT).show();
    finish();
}

設(shè)置BLE

整個設(shè)備只有一個BluetoothAdapter

1. 獲取BluetoothAdapter
   整個設(shè)備只有一個BluetoothAdapter，它代表了設(shè)備自己的藍(lán)牙適配器碗誉，應(yīng)用通過這個對象與設(shè)備進(jìn)行交互召嘶。

// Initializes Bluetooth adapter.
final BluetoothManager bluetoothManager =
        (BluetoothManager) getSystemService(Context.BLUETOOTH_SERVICE);
mBluetoothAdapter = bluetoothManager.getAdapter();

• 開啟藍(lán)牙

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);
}

查找BLE設(shè)備

要查找BLE設(shè)備，需要使用startLeScan()方法哮缺，它的參數(shù)是BluetoothAdapter.LeScanCallback弄跌。你必須實(shí)現(xiàn)這個callbak，因?yàn)檫@是掃描結(jié)果返回的方式尝苇。藍(lán)牙掃描是一個電量敏感的操作铛只，你需要遵守以下指導(dǎo)：

• 只要找到了要找的設(shè)備，停止掃描
• 不要在循環(huán)里掃描糠溜，設(shè)置一個掃描時間淳玩。之前的設(shè)備可能已經(jīng)移動到范圍外，持續(xù)掃描會耗盡電量非竿。

如何開始和停止掃描：

/**
 * 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);
        }
        ...
    }
...
}

如果只想掃描指定類型的外圍設(shè)備蜕着，你可以調(diào)用startLeScan(UUID[], BluetoothAdapter.LeScanCallback)，提供一個指定了你app支持的GATT服務(wù)的UUID數(shù)組對象红柱。

下面是一個用來傳送BLE掃描結(jié)果的接口BluetoothAdapter.LeScanCallback的實(shí)現(xiàn)：

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：你只能掃描BLE設(shè)備或傳統(tǒng)藍(lán)牙設(shè)備二者之一承匣，就像 Bluetooth描述的那樣。你不能同時掃描兩種設(shè)備锤悄。

連接GATT服務(wù)端

與BLE設(shè)備交互第一步就是要連接它—更確切的說韧骗，是連接到設(shè)備上的GATT服務(wù)端。要連接到BLE設(shè)備的GATT服務(wù)端零聚，使用[connectGatt()](https://developer.android.com/reference/android/bluetooth/BluetoothDevice.html#connectGatt(android.content.Context, boolean, android.bluetooth.BluetoothGattCallback))方法袍暴。這個方法需要三個參數(shù)，一個Context對象隶症，autoConnect（一個指示是否自動連接到BLE設(shè)備--當(dāng)它一旦可用的時候--的布爾值）容诬，和一個 BluetoothGattCallback的引用：

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

返回的BluetoothGatt實(shí)例之后你可以用它來管理GATT客戶端的操作。調(diào)用者（Android app)是GATT客戶端沿腰。 BluetoothGattCallback
用于傳遞結(jié)果給用戶览徒，例如連接狀態(tài)，以及任何進(jìn)一步GATT客戶端操作颂龙。

在這個例子中习蓬，這個BLE APP提供了一個activity（DeviceControlActivity)來連接纽什，顯示數(shù)據(jù)，顯示該設(shè)備支持的GATT services和characteristics躲叼。根據(jù)用戶的輸入芦缰，這個activity與一個叫做BluetoothLeService的 Service通信，它通過Android BLE API實(shí)現(xiàn)與BLE設(shè)備交互：

// 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);
            }
        }
     ...
    };
...
}

當(dāng)一個特定的回調(diào)被觸發(fā)的時候枫慷，它會調(diào)用相應(yīng)的broadcastUpdate()輔助方法并且傳遞給它一個action让蕾。注意在該部分中的數(shù)據(jù)解析按照藍(lán)牙心率測量配置文件規(guī)格profile specifications進(jìn)行。

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);
}

返回到DeviceControlActivity, 這些事件由一個BroadcastReceiver來處理:

// 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));
        }
    }
};

讀取BLE屬性

一旦你的Android app已經(jīng)連接到GATT服務(wù)端連接且發(fā)現(xiàn)services后或听，就可以讀探孝、寫那些支持的屬性。例如誉裆，這段代碼遍歷服務(wù)端的services和 characteristics顿颅，并且將它們顯示在UI上。

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

常見的需求是當(dāng)設(shè)備上的特性改變時通知BLE應(yīng)用程序足丢。這段代碼展示了如何使用 [setCharacteristicNotification()](https://developer.android.com/reference/android/bluetooth/BluetoothGatt.html#setCharacteristicNotification(android.bluetooth.BluetoothGattCharacteristic, boolean)) 給一個特性設(shè)置通知粱腻。

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);

一旦對一個特性啟用了通知，當(dāng)遠(yuǎn)程藍(lán)牙設(shè)備特性發(fā)生變化時斩跌，回調(diào)函數(shù)[onCharacteristicChanged( )](http://developer.android.com/reference/android/bluetooth/BluetoothGattCallback.html#onCharacteristicChanged(android.bluetooth.BluetoothGatt, android.bluetooth.BluetoothGattCharacteristic))就會被觸發(fā)：

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

關(guān)閉客戶端App

一旦你的app完成了對BLE設(shè)備的使用绍些，需要調(diào)用close()以便系統(tǒng)能適當(dāng)?shù)蒯尫刨Y源：

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

參考鏈接：
https://developer.android.com/guide/topics/connectivity/bluetooth-le.html