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蓝牙低功耗概览

Android 4.3(API 级别 18)为发挥核心作用的蓝牙低功耗 (BLE) 引入内置平台支持,并提供相应 API,方便应用发现设备、查询服务和传输信息。

常见用例包括:

  • 在临近设备间传输少量数据。
  • Google Beacons 等近程传感器交互,以便为用户提供基于其当前位置的自定义体验。

传统蓝牙不同,蓝牙低功耗 (BLE) 旨在提供显著降低的功耗。这使 Android 应用可与功率要求更严格的 BLE 设备(例如近程传感器、心率监测仪和健身设备)通信。

注意:当用户使用 BLE 将其设备与其他设备配对时,用户设备上的所有应用都可以访问在这两个设备间传输的数据。

因此,如果您的应用捕获敏感数据,您应实现应用层安全以保护此类数据的私密性。

关键术语和概念

以下是对 BLE 关键术语和概念的总结:

  • 通用属性配置文件 (GATT) — GATT 配置文件是一种通用规范,内容针对在 BLE 链路上发送和接收称为“属性”的简短数据片段。目前所有低功耗应用配置文件均以 GATT 为基础。
    • 蓝牙特别兴趣小组 (Bluetooth SIG) 为低功耗设备定义诸多配置文件。配置文件是描述设备如何在特定应用中工作的规范。请注意,一台设备可以实现多个配置文件。例如,一台设备可能包含心率监测仪和电池电量检测器。
  • 属性协议 (ATT) — 属性协议 (ATT) 是 GATT 的构建基础,二者的关系也被称为 GATT/ATT。ATT 经过优化,可在 BLE 设备上运行。为此,该协议尽可能少地使用字节。每个属性均由通用唯一标识符 (UUID) 进行唯一标识,后者是用于对信息进行唯一标识的字符串 ID 的 128 位标准化格式。由 ATT 传输的属性采用特征服务格式。
  • 特征 — 特征包含一个值和 0 至多个描述特征值的描述符。您可将特征理解为类型,后者与类类似。 
  • 描述符 — 描述符是描述特征值的已定义属性。例如,描述符可指定人类可读的描述、特征值的可接受范围或特定于特征值的度量单位。
  • Service — 服务是一系列特征。例如,您可能拥有名为“心率监测器”的服务,其中包括“心率测量”等特征。您可以在 bluetooth.org 上找到基于 GATT 的现有配置文件和服务的列表。

角色和职责

以下是 Android 设备与 BLE 设备交互时应用的角色和职责:

  • 中央与外围。这适用于 BLE 连接本身。担任中央角色的设备进行扫描、寻找广播;外围设备发出广播。
  • GATT 服务器与 GATT 客户端。这确定两个设备建立连接后如何相互通信。

要了解两者的区别,请想象您有一部 Android 手机和一个 Activity 追踪器,该 Activity 追踪器是一个 BLE 设备。手机支持中央角色;Activity 追踪器支持外围角色(要建立 BLE 连接必须具备这两个两个角色—如果两个设备都仅支持中央或外围角色,则无法相互通信)。

手机与 Activity 追踪器建立连接后,它们便开始相互传送 GATT 数据。根据它们传送数据的种类,其中一个会充当 GATT 服务器。例如,如果 Activity 追踪器要将传感器数据汇报给手机,那么 Activity 追踪器便充当服务器。如果 Activity 追踪器要从手机接收更新,那么手机便充当服务器。

在本文档中使用的示例中,Android 应用(在 Android 设备上运行)是 GATT 客户端。该应用从 GATT 服务器获取数据,后者是一个支持 Heart Rate Profile 的心率监测仪。但您也可以设计您​的 Andr​​oid 应用,使它充当 GATT 服务器角色。如需了解详情,请参阅 BluetoothGattServer

BLE 权限

要在您的应用中使用蓝牙功能,您必须声明 BLUETOOTH 蓝牙权限。您需要此权限才能执行任何蓝牙通信,例如请求连接、接受连接和传输数据等。

考虑到 LE 信标通常与位置相关联,您还须声明 ACCESS_FINE_LOCATION 权限。没有此权限,扫描将无法返回任何结果。

注意:如果您的应用适配 Android 9(API 级别 28)或更低版本,则您可以声明 ACCESS_COARSE_LOCATION 权限而非 ACCESS_FINE_LOCATION 权限。

如果您想让应用启动设备发现或操纵蓝牙设置,则您还须声明 BLUETOOTH_ADMIN 权限。注意:如果使用 BLUETOOTH_ADMIN 权限,则您必须拥有 BLUETOOTH 权限。

在应用清单文件中声明蓝牙权限。例如:

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

<!-- If your app targets Android 9 or lower, you can declare
     ACCESS_COARSE_LOCATION instead. -->
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />

如果您要声明您的应用仅适用于支持 BLE 的设备,请在应用清单中添加以下内容:

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

如果您希望应用适用于不支持 BLE 的设备,则您应仍将此元素添加到应用清单中,但设置 required="false"。然后您可以在运行时使用 PackageManager.hasSystemFeature() 确定 BLE 的可用性:

Kotlin

private fun PackageManager.missingSystemFeature(name: String): Boolean = !hasSystemFeature(name)
...

packageManager.takeIf { it.missingSystemFeature(PackageManager.FEATURE_BLUETOOTH_LE) }?.also {
    Toast.makeText(this, R.string.ble_not_supported, Toast.LENGTH_SHORT).show()
    finish()
}

Java

// 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();
}

设置 BLE

在您的应用程序可以通过 BLE 进行通信之前,您需验证设备是否支持 BLE,如果支持,请确保该功能已启用。请注意,仅当 <uses-feature.../> 设置为 false 时才需要进行此检查。

如果不支持 BLE,则应妥善停用任何 BLE 功能。如果设备支持 BLE 但已停用此功能,则您可以请求用户在不离开应用的同时启用蓝牙。借助 BluetoothAdapter,您可以分两步完成此设置。

  1. 获取 BluetoothAdapter

    所有蓝牙 Activity 都需要 BluetoothAdapterBluetoothAdapter 代表设备自身的蓝牙适配器(蓝牙无线装置)。整个系统有一个蓝牙适配器,并且您的应用可使用此对象与之进行交互。以下代码段展示如何获取适配器。请注意,此方法使用 getSystemService() 返回 BluetoothManager 的实例,然后使用该实例获取适配器。Android 4.3(API 级别 18)引入 BluetoothManager

    Kotlin

    private val bluetoothAdapter: BluetoothAdapter? by lazy(LazyThreadSafetyMode.NONE) {
        val bluetoothManager = getSystemService(Context.BLUETOOTH_SERVICE) as BluetoothManager
        bluetoothManager.adapter
    }
    

    Java

    private BluetoothAdapter bluetoothAdapter;
    ...
    // Initializes Bluetooth adapter.
    final BluetoothManager bluetoothManager =
            (BluetoothManager) getSystemService(Context.BLUETOOTH_SERVICE);
    bluetoothAdapter = bluetoothManager.getAdapter();
    
  2. 启用蓝牙

    下一步,您需要确保蓝牙已启用。调用 isEnabled(),以检查当前是否已启用蓝牙。如果此方法返回 false,则表示蓝牙处于停用状态。以下代码段会检查蓝牙是否已启用。如果并未启用,则代码段会显示错误,提示用户前往“Settings”启用蓝牙:

    Kotlin

    private val BluetoothAdapter.isDisabled: Boolean
        get() = !isEnabled
    ...
    
    // Ensures Bluetooth is available on the device and it is enabled. If not,
    // displays a dialog requesting user permission to enable Bluetooth.
    bluetoothAdapter?.takeIf { it.isDisabled }?.apply {
        val enableBtIntent = Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE)
        startActivityForResult(enableBtIntent, REQUEST_ENABLE_BT)
    }
    

    Java

    // Ensures Bluetooth is available on the device and it is enabled. If not,
    // displays a dialog requesting user permission to enable Bluetooth.
    if (bluetoothAdapter == null || !bluetoothAdapter.isEnabled()) {
        Intent enableBtIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
        startActivityForResult(enableBtIntent, REQUEST_ENABLE_BT);
    }
    

    注意:传递给 startActivityForResult(android.content.Intent, int)REQUEST_ENABLE_BT 常量是本地定义的整数(必须大于0),系统会在您的 onActivityResult(int, int, android.content.Intent) 实现中将其作为 requestCode 参数传回给您。

查找 BLE 设备

如要查找 BLE 设备,请使用 startLeScan() 方法。此方法将 BluetoothAdapter.LeScanCallback 作为参数。您必须实现此回调,因为这是返回扫描结果的方式。扫描非常耗电,因此您应遵循以下准则:

  • 找到所需设备后,立即停止扫描。
  • 绝对不进行循环扫描,并设置扫描时间限制。之前可用的设备可能已超出范围,继续扫描会耗尽电池电量。

以下代码段展示如何启动和停止扫描:

Kotlin

private const val SCAN_PERIOD: Long = 10000

/**
 * Activity for scanning and displaying available BLE devices.
 */
class DeviceScanActivity(
        private val bluetoothAdapter: BluetoothAdapter,
        private val handler: Handler
) : ListActivity() {

    private var mScanning: Boolean = false

    private fun scanLeDevice(enable: Boolean) {
        when (enable) {
            true -> {
                // Stops scanning after a pre-defined scan period.
                handler.postDelayed({
                    mScanning = false
                    bluetoothAdapter.stopLeScan(leScanCallback)
                }, SCAN_PERIOD)
                mScanning = true
                bluetoothAdapter.startLeScan(leScanCallback)
            }
            else -> {
                mScanning = false
                bluetoothAdapter.stopLeScan(leScanCallback)
            }
        }
    }
}

Java

/**
 * Activity for scanning and displaying available BLE devices.
 */
public class DeviceScanActivity extends ListActivity {

    private BluetoothAdapter bluetoothAdapter;
    private boolean mScanning;
    private Handler handler;

    // 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.
            handler.postDelayed(new Runnable() {
                @Override
                public void run() {
                    mScanning = false;
                    bluetoothAdapter.stopLeScan(leScanCallback);
                }
            }, SCAN_PERIOD);

            mScanning = true;
            bluetoothAdapter.startLeScan(leScanCallback);
        } else {
            mScanning = false;
            bluetoothAdapter.stopLeScan(leScanCallback);
        }
        ...
    }
...
}

如果您想扫描特定类型的外围设备,则可调用 startLeScan(UUID[], BluetoothAdapter.LeScanCallback),它会提供一组 UUID 对象,用于指定您的应用支持的 GATT 服务。

以下是 BluetoothAdapter.LeScanCallback 的实现,其为用于传递 BLE 扫描结果的界面:

Kotlin

val leDeviceListAdapter: LeDeviceListAdapter = ...

private val leScanCallback = BluetoothAdapter.LeScanCallback { device, rssi, scanRecord ->
    runOnUiThread {
        leDeviceListAdapter.addDevice(device)
        leDeviceListAdapter.notifyDataSetChanged()
    }
}

Java

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

注意:您仅能扫描蓝牙 LE 设备传统蓝牙设备,正如蓝牙概览中所述。您无法同时扫描蓝牙 LE 设备和传统蓝牙设备。

连接到 GATT 服务器

与 BLE 设备交互的第一步便是连接到 GATT 服务器。更具体地说,是连接到设备上的 GATT 服务器。如要连接到 BLE 设备上的 GATT 服务器,请使用 connectGatt() 方法。此方法采用三个参数:一个 Context 对象、autoConnect(布尔值,指示是否在可用时自动连接到 BLE 设备),以及对 BluetoothGattCallback 的引用:

Kotlin

var bluetoothGatt: BluetoothGatt? = null
...

bluetoothGatt = device.connectGatt(this, false, gattCallback)

Java

bluetoothGatt = device.connectGatt(this, false, gattCallback);

这将连接到由 BLE 设备托管的 GATT 服务器,并返回 BluetoothGatt 实例,然后您可使用该实例执行 GATT 客户端操作。调用方(Android 应用)是 GATT 客户端。BluetoothGattCallback 用于向客户端传递结果(例如连接状态),以及任何进一步的 GATT 客户端操作。

在本例中,BLE 应用提供一个 Activity (DeviceControlActivity) 来连接、显示数据和显示设备支持的 GATT 服务和特征。根据用户输入,此 Activity 和一个名为 BluetoothLeServiceService 通信,该服务通过 Android BLE API 与 BLE 设备交互:

Kotlin

private val TAG = BluetoothLeService::class.java.simpleName
private const val STATE_DISCONNECTED = 0
private const val STATE_CONNECTING = 1
private const val STATE_CONNECTED = 2
const val ACTION_GATT_CONNECTED = "com.example.bluetooth.le.ACTION_GATT_CONNECTED"
const val ACTION_GATT_DISCONNECTED = "com.example.bluetooth.le.ACTION_GATT_DISCONNECTED"
const val ACTION_GATT_SERVICES_DISCOVERED =
        "com.example.bluetooth.le.ACTION_GATT_SERVICES_DISCOVERED"
const val ACTION_DATA_AVAILABLE = "com.example.bluetooth.le.ACTION_DATA_AVAILABLE"
const val EXTRA_DATA = "com.example.bluetooth.le.EXTRA_DATA"
val UUID_HEART_RATE_MEASUREMENT = UUID.fromString(SampleGattAttributes.HEART_RATE_MEASUREMENT)

// A service that interacts with the BLE device via the Android BLE API.
class BluetoothLeService(private var bluetoothGatt: BluetoothGatt?) : Service() {

    private var connectionState = STATE_DISCONNECTED

    // Various callback methods defined by the BLE API.
    private val gattCallback = object : BluetoothGattCallback() {
        override fun onConnectionStateChange(
                gatt: BluetoothGatt,
                status: Int,
                newState: Int
        ) {
            val intentAction: String
            when (newState) {
                BluetoothProfile.STATE_CONNECTED -> {
                    intentAction = ACTION_GATT_CONNECTED
                    connectionState = STATE_CONNECTED
                    broadcastUpdate(intentAction)
                    Log.i(TAG, "Connected to GATT server.")
                    Log.i(TAG, "Attempting to start service discovery: " +
                            bluetoothGatt?.discoverServices())
                }
                BluetoothProfile.STATE_DISCONNECTED -> {
                    intentAction = ACTION_GATT_DISCONNECTED
                    connectionState = STATE_DISCONNECTED
                    Log.i(TAG, "Disconnected from GATT server.")
                    broadcastUpdate(intentAction)
                }
            }
        }

        // New services discovered
        override fun onServicesDiscovered(gatt: BluetoothGatt, status: Int) {
            when (status) {
                BluetoothGatt.GATT_SUCCESS -> broadcastUpdate(ACTION_GATT_SERVICES_DISCOVERED)
                else -> Log.w(TAG, "onServicesDiscovered received: $status")
            }
        }

        // Result of a characteristic read operation
        override fun onCharacteristicRead(
                gatt: BluetoothGatt,
                characteristic: BluetoothGattCharacteristic,
                status: Int
        ) {
            when (status) {
                    BluetoothGatt.GATT_SUCCESS -> {
                        broadcastUpdate(ACTION_DATA_AVAILABLE, characteristic)
                    }
            }
        }
    }
}

Java

// 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 bluetoothManager;
    private BluetoothAdapter bluetoothAdapter;
    private String bluetoothDeviceAddress;
    private BluetoothGatt bluetoothGatt;
    private int connectionState = 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 gattCallback =
            new BluetoothGattCallback() {
        @Override
        public void onConnectionStateChange(BluetoothGatt gatt, int status,
                int newState) {
            String intentAction;
            if (newState == BluetoothProfile.STATE_CONNECTED) {
                intentAction = ACTION_GATT_CONNECTED;
                connectionState = STATE_CONNECTED;
                broadcastUpdate(intentAction);
                Log.i(TAG, "Connected to GATT server.");
                Log.i(TAG, "Attempting to start service discovery:" +
                        bluetoothGatt.discoverServices());

            } else if (newState == BluetoothProfile.STATE_DISCONNECTED) {
                intentAction = ACTION_GATT_DISCONNECTED;
                connectionState = 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);
            }
        }
     ...
    };
...
}

当一个特定回调被触发时,它会调用相应的 broadcastUpdate() 辅助方法并向其传递操作。请注意,本部分的数据解析参照“蓝牙心率测量”配置文件规范执行:

Kotlin

private fun broadcastUpdate(action: String) {
    val intent = Intent(action)
    sendBroadcast(intent)
}

private fun broadcastUpdate(action: String, characteristic: BluetoothGattCharacteristic) {
    val intent = Intent(action)

    // This is special handling for the Heart Rate Measurement profile. Data
    // parsing is carried out as per profile specifications.
    when (characteristic.uuid) {
        UUID_HEART_RATE_MEASUREMENT -> {
            val flag = characteristic.properties
            val format = when (flag and 0x01) {
                0x01 -> {
                    Log.d(TAG, "Heart rate format UINT16.")
                    BluetoothGattCharacteristic.FORMAT_UINT16
                }
                else -> {
                    Log.d(TAG, "Heart rate format UINT8.")
                    BluetoothGattCharacteristic.FORMAT_UINT8
                }
            }
            val heartRate = characteristic.getIntValue(format, 1)
            Log.d(TAG, String.format("Received heart rate: %d", heartRate))
            intent.putExtra(EXTRA_DATA, (heartRate).toString())
        }
        else -> {
            // For all other profiles, writes the data formatted in HEX.
            val data: ByteArray? = characteristic.value
            if (data?.isNotEmpty() == true) {
                val hexString: String = data.joinToString(separator = " ") {
                    String.format("%02X", it)
                }
                intent.putExtra(EXTRA_DATA, "$data\n$hexString")
            }
        }

    }
    sendBroadcast(intent)
}

Java

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);
}

回到 DeviceControlActivity,这些事件由 BroadcastReceiver 处理:

Kotlin

// 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 val gattUpdateReceiver = object : BroadcastReceiver() {

    private lateinit var bluetoothLeService: BluetoothLeService

    override fun onReceive(context: Context, intent: Intent) {
        val action = intent.action
        when (action){
            ACTION_GATT_CONNECTED -> {
                connected = true
                updateConnectionState(R.string.connected)
                (context as? Activity)?.invalidateOptionsMenu()
            }
            ACTION_GATT_DISCONNECTED -> {
                connected = false
                updateConnectionState(R.string.disconnected)
                (context as? Activity)?.invalidateOptionsMenu()
                clearUI()
            }
            ACTION_GATT_SERVICES_DISCOVERED -> {
                // Show all the supported services and characteristics on the
                // user interface.
                displayGattServices(bluetoothLeService.getSupportedGattServices())
            }
            ACTION_DATA_AVAILABLE -> {
                displayData(intent.getStringExtra(BluetoothLeService.EXTRA_DATA))
            }
        }
    }
}

Java

// 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 gattUpdateReceiver = new BroadcastReceiver() {
    @Override
    public void onReceive(Context context, Intent intent) {
        final String action = intent.getAction();
        if (BluetoothLeService.ACTION_GATT_CONNECTED.equals(action)) {
            connected = true;
            updateConnectionState(R.string.connected);
            invalidateOptionsMenu();
        } else if (BluetoothLeService.ACTION_GATT_DISCONNECTED.equals(action)) {
            connected = 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(bluetoothLeService.getSupportedGattServices());
        } else if (BluetoothLeService.ACTION_DATA_AVAILABLE.equals(action)) {
            displayData(intent.getStringExtra(BluetoothLeService.EXTRA_DATA));
        }
    }
};

读取 BLE 属性

当您的 Android 应用成功连接到 GATT 服务器并发现服务后,应用便可在支持的位置读取和写入属性。例如,以下代码段遍历服务器的服务和特征,并在界面中将其显示出来:

Kotlin

class DeviceControlActivity : 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 fun displayGattServices(gattServices: List<BluetoothGattService>?) {
        if (gattServices == null) return
        var uuid: String?
        val unknownServiceString: String = resources.getString(R.string.unknown_service)
        val unknownCharaString: String = resources.getString(R.string.unknown_characteristic)
        val gattServiceData: MutableList<HashMap<String, String>> = mutableListOf()
        val gattCharacteristicData: MutableList<ArrayList<HashMap<String, String>>> =
                mutableListOf()
        mGattCharacteristics = mutableListOf()

        // Loops through available GATT Services.
        gattServices.forEach { gattService ->
            val currentServiceData = HashMap<String, String>()
            uuid = gattService.uuid.toString()
            currentServiceData[LIST_NAME] = SampleGattAttributes.lookup(uuid, unknownServiceString)
            currentServiceData[LIST_UUID] = uuid
            gattServiceData += currentServiceData

            val gattCharacteristicGroupData: ArrayList<HashMap<String, String>> = arrayListOf()
            val gattCharacteristics = gattService.characteristics
            val charas: MutableList<BluetoothGattCharacteristic> = mutableListOf()

            // Loops through available Characteristics.
            gattCharacteristics.forEach { gattCharacteristic ->
                charas += gattCharacteristic
                val currentCharaData: HashMap<String, String> = hashMapOf()
                uuid = gattCharacteristic.uuid.toString()
                currentCharaData[LIST_NAME] = SampleGattAttributes.lookup(uuid, unknownCharaString)
                currentCharaData[LIST_UUID] = uuid
                gattCharacteristicGroupData += currentCharaData
            }
            mGattCharacteristics += charas
            gattCharacteristicData += gattCharacteristicGroupData
        }
    }
}

Java


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

BLE 应用通常会要求在设备上的特定特征发生变化时收到通知。以下代码段展示如何使用 setCharacteristicNotification() 方法设置特征的通知:

Kotlin

lateinit var bluetoothGatt: BluetoothGatt
lateinit var characteristic: BluetoothGattCharacteristic
var enabled: Boolean = true
...
bluetoothGatt.setCharacteristicNotification(characteristic, enabled)
val uuid: UUID = UUID.fromString(SampleGattAttributes.CLIENT_CHARACTERISTIC_CONFIG)
val descriptor = characteristic.getDescriptor(uuid).apply {
    value = BluetoothGattDescriptor.ENABLE_NOTIFICATION_VALUE
}
bluetoothGatt.writeDescriptor(descriptor)

Java

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

为某个特征启用通知后,如果远程设备上的特征发生更改,则会触发 onCharacteristicChanged() 回调:

Kotlin

// Characteristic notification
override fun onCharacteristicChanged(
        gatt: BluetoothGatt,
        characteristic: BluetoothGattCharacteristic
) {
    broadcastUpdate(ACTION_DATA_AVAILABLE, characteristic)
}

Java

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

关闭客户端应用

当应用完成对 BLE 设备的使用后,其应调用 close(),以便系统可以适当地释放资源:

Kotlin

fun close() {
    bluetoothGatt?.close()
    bluetoothGatt = null
}

Java

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