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连接到 GATT 服务器

与 BLE 设备交互的第一步是连接该设备。更具体地说，就是连接到设备上的 GATT 服务器。如需连接到 BLE 设备上的 GATT 服务器，请使用 connectGatt() 方法。此方法接受三个参数：Context 对象、autoConnect（一个布尔值，指示是否在 BLE 设备可用后立即自动连接到 BLE 设备）和对 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，您随后可以使用该实例执行 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。

设置绑定服务

在以下示例中，BLE 应用提供了一个 activity (DeviceControlActivity)，用于连接到蓝牙设备、显示设备数据以及显示设备支持的 GATT 服务和特性。根据用户输入，此 activity 与名为 BluetoothLeService 的 Service 通信，后者通过 BLE API 与 BLE 设备进行交互。通信使用绑定服务执行，绑定服务允许 activity 连接到 BluetoothLeService 并调用函数连接到设备。BluetoothLeService 需要一个 Binder 实现，该实现可提供对 activity 服务的访问权限。

Kotlin

class BluetoothLeService : Service() {

    private val binder = LocalBinder()

    override fun onBind(intent: Intent): IBinder? {
        return binder
    }

    inner class LocalBinder : Binder() {
        fun getService() : BluetoothLeService {
            return this@BluetoothLeService
        }
    }
}

Java

class BluetoothLeService extends Service {

    private Binder binder = new LocalBinder();

    @Nullable
    @Override
    public IBinder onBind(Intent intent) {
        return binder;
    }

    class LocalBinder extends Binder {
        public BluetoothLeService getService() {
            return BluetoothLeService.this;
        }
    }
}

activity 可以使用 bindService() 启动服务，传递 Intent 来启动服务，传入 ServiceConnection 实现来监听连接和断开连接事件，以及传递标志来指定其他连接选项。

Kotlin

class DeviceControlActivity : AppCompatActivity() {

    private var bluetoothService : BluetoothLeService? = null

    // Code to manage Service lifecycle.
    private val serviceConnection: ServiceConnection = object : ServiceConnection {
        override fun onServiceConnected(
            componentName: ComponentName,
            service: IBinder
        ) {
            bluetoothService = (service as LocalBinder).getService()
            bluetoothService?.let { bluetooth ->
                // call functions on service to check connection and connect to devices
            }
        }

        override fun onServiceDisconnected(componentName: ComponentName) {
            bluetoothService = null
        }
    }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.gatt_services_characteristics)

        val gattServiceIntent = Intent(this, BluetoothLeService::class.java)
        bindService(gattServiceIntent, serviceConnection, Context.BIND_AUTO_CREATE)
    }
}

Java

class DeviceControlActivity extends AppCompatActivity {

    private BluetoothLeService bluetoothService;

    private ServiceConnection serviceConnection = new ServiceConnection() {
        @Override
        public void onServiceConnected(ComponentName name, IBinder service) {
            bluetoothService = ((LocalBinder) service).getService();
            if (bluetoothService != null) {
                // call functions on service to check connection and connect to devices
            }
        }

        @Override
        public void onServiceDisconnected(ComponentName name) {
            bluetoothService = null;
        }
    };

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.gatt_services_characteristics);

        Intent gattServiceIntent = new Intent(this, BluetoothLeService.class);
        bindService(gattServiceIntent, serviceConnection, Context.BIND_AUTO_CREATE);
    }
}

设置 BluetoothAdapter

服务被绑定后，需要访问 BluetoothAdapter。系统应检查适配器是否在设备上可用。如需详细了解 BluetoothAdapter，请参阅设置蓝牙。以下示例将此设置代码封装在 initialize() 函数中，该函数会返回指示成功的 Boolean 值。

Kotlin

private const val TAG = "BluetoothLeService"

class BluetoothLeService : Service() {

    private var bluetoothAdapter: BluetoothAdapter? = null

    fun initialize(): Boolean {
        bluetoothAdapter = BluetoothAdapter.getDefaultAdapter()
        if (bluetoothAdapter == null) {
            Log.e(TAG, "Unable to obtain a BluetoothAdapter.")
            return false
        }
        return true
    }

    ...
}

Java

class BluetoothLeService extends Service {

    public static final String TAG = "BluetoothLeService";

    private BluetoothAdapter bluetoothAdapter;

    public boolean initialize() {
        bluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
        if (bluetoothAdapter == null) {
            Log.e(TAG, "Unable to obtain a BluetoothAdapter.");
            return false;
        }
        return true;
    }

    ...
}

此 activity 将在其 ServiceConnection 实现中调用此函数。处理 initialize() 函数的 false 返回值取决于您的应用。您可以向用户显示错误消息，指出当前设备不支持蓝牙操作或停用任何需要蓝牙功能的功能。在以下示例中，系统将对 activity 调用 finish()，以便用户返回上一屏幕。

Kotlin

class DeviceControlActivity : AppCompatActivity() {

    // Code to manage Service lifecycle.
    private val serviceConnection: ServiceConnection = object : ServiceConnection {
        override fun onServiceConnected(
            componentName: ComponentName,
            service: IBinder
        ) {
            bluetoothService = (service as LocalBinder).getService()
            bluetoothService?.let { bluetooth ->
                if (!bluetooth.initialize()) {
                    Log.e(TAG, "Unable to initialize Bluetooth")
                    finish()
                }
                // perform device connection
            }
        }

        override fun onServiceDisconnected(componentName: ComponentName) {
            bluetoothService = null
        }
    }

    ...
}

Java

class DeviceControlsActivity extends AppCompatActivity {

    private ServiceConnection serviceConnection = new ServiceConnection() {
        @Override
        public void onServiceConnected(ComponentName name, IBinder service) {
            bluetoothService = ((LocalBinder) service).getService();
            if (bluetoothService != null) {
                if (!bluetoothService.initialize()) {
                    Log.e(TAG, "Unable to initialize Bluetooth");
                    finish();
                }
                // perform device connection
            }
        }

        @Override
        public void onServiceDisconnected(ComponentName name) {
            bluetoothService = null;
        }
    };

    ...
}

连接到设备

BluetoothLeService 实例初始化后，即可连接到 BLE 设备。activity 需要将设备地址发送给服务，以便发起连接。服务将首先对 BluetoothAdapter 调用 getRemoteDevice() 以访问设备。如果适配器找不到具有该地址的设备，getRemoteDevice() 会抛出 IllegalArgumentException。

Kotlin

fun connect(address: String): Boolean {
    bluetoothAdapter?.let { adapter ->
        try {
            val device = adapter.getRemoteDevice(address)
        } catch (exception: IllegalArgumentException) {
            Log.w(TAG, "Device not found with provided address.")
            return false
        }
    // connect to the GATT server on the device
    } ?: run {
        Log.w(TAG, "BluetoothAdapter not initialized")
        return false
    }
}

Java

public boolean connect(final String address) {
    if (bluetoothAdapter == null || address == null) {
        Log.w(TAG, "BluetoothAdapter not initialized or unspecified address.");
        return false;
    }

    try {
        final BluetoothDevice device = bluetoothAdapter.getRemoteDevice(address);
    } catch (IllegalArgumentException exception) {
        Log.w(TAG, "Device not found with provided address.");
        return false;
    }
    // connect to the GATT server on the device
}

服务初始化后，DeviceControlActivity 会调用此 connect() 函数。activity 需要传入 BLE 设备的地址。在以下示例中，设备地址将作为 intent extra 传递给 activity。

Kotlin

// Code to manage Service lifecycle.
private val serviceConnection: ServiceConnection = object : ServiceConnection {
    override fun onServiceConnected(
    componentName: ComponentName,
    service: IBinder
    ) {
        bluetoothService = (service as LocalBinder).getService()
        bluetoothService?.let { bluetooth ->
            if (!bluetooth.initialize()) {
                Log.e(TAG, "Unable to initialize Bluetooth")
                finish()
            }
            // perform device connection
            bluetooth.connect(deviceAddress)
        }
    }

    override fun onServiceDisconnected(componentName: ComponentName) {
        bluetoothService = null
    }
}

Java

private ServiceConnection serviceConnection = new ServiceConnection() {
    @Override
    public void onServiceConnected(ComponentName name, IBinder service) {
        bluetoothService = ((LocalBinder) service).getService();
        if (bluetoothService != null) {
            if (!bluetoothService.initialize()) {
                Log.e(TAG, "Unable to initialize Bluetooth");
                finish();
            }
            // perform device connection
            bluetoothService.connect(deviceAddress);
        }
    }

    @Override
    public void onServiceDisconnected(ComponentName name) {
        bluetoothService = null;
    }
};

声明 GATT 回调

一旦 activity 告知服务应连接到哪个设备且服务连接到该设备，服务便需要连接到 BLE 设备上的 GATT 服务器。此连接需要 BluetoothGattCallback 以接收有关连接状态、服务发现、特征读取和特征通知的通知。

本主题重点介绍连接状态通知。如需了解如何执行服务发现、特征读取和请求特征通知，请参阅传输 BLE 数据。

当与设备 GATT 服务器的连接更改时，会触发 onConnectionStateChange() 函数。在以下示例中，回调是在 Service 类中定义的，因此可在服务连接到 BluetoothDevice 后将其与它一起使用。

Kotlin

private val bluetoothGattCallback = object : BluetoothGattCallback() {
    override fun onConnectionStateChange(gatt: BluetoothGatt?, status: Int, newState: Int) {
        if (newState == BluetoothProfile.STATE_CONNECTED) {
            // successfully connected to the GATT Server
        } else if (newState == BluetoothProfile.STATE_DISCONNECTED) {
            // disconnected from the GATT Server
        }
    }
}

Java

private final BluetoothGattCallback bluetoothGattCallback = new BluetoothGattCallback() {
    @Override
    public void onConnectionStateChange(BluetoothGatt gatt, int status, int newState) {
        if (newState == BluetoothProfile.STATE_CONNECTED) {
            // successfully connected to the GATT Server
        } else if (newState == BluetoothProfile.STATE_DISCONNECTED) {
            // disconnected from the GATT Server
        }
    }
};

连接到 GATT 服务

声明 BluetoothGattCallback 后，该服务就可以使用 connect() 函数中的 BluetoothDevice 对象连接到设备上的 GATT 服务。

使用 connectGatt() 函数。这需要 Context 对象、autoConnect 布尔值标志和 BluetoothGattCallback。在此示例中，应用直接连接到 BLE 设备，因此针对 autoConnect 传递了 false。

此外，还添加了 BluetoothGatt 属性。这样一来，服务便可以在不再需要时关闭连接。

Kotlin

class BluetoothLeService : Service() {

...

    private var bluetoothGatt: BluetoothGatt? = null

    ...

    fun connect(address: String): Boolean {
        bluetoothAdapter?.let { adapter ->
            try {
                val device = adapter.getRemoteDevice(address)
                // connect to the GATT server on the device
                bluetoothGatt = device.connectGatt(this, false, bluetoothGattCallback)
                return true
            } catch (exception: IllegalArgumentException) {
                Log.w(TAG, "Device not found with provided address.  Unable to connect.")
                return false
            }
        } ?: run {
            Log.w(TAG, "BluetoothAdapter not initialized")
            return false
        }
    }
}

Java

class BluetoothLeService extends Service {

...

    private BluetoothGatt bluetoothGatt;

    ...

    public boolean connect(final String address) {
        if (bluetoothAdapter == null || address == null) {
            Log.w(TAG, "BluetoothAdapter not initialized or unspecified address.");
            return false;
        }
        try {
            final BluetoothDevice device = bluetoothAdapter.getRemoteDevice(address);
            // connect to the GATT server on the device
            bluetoothGatt = device.connectGatt(this, false, bluetoothGattCallback);
            return true;
        } catch (IllegalArgumentException exception) {
            Log.w(TAG, "Device not found with provided address.  Unable to connect.");
            return false;
        }
    }
}

广播动态

当服务器与 GATT 服务器连接或断开连接时，需要通知 activity 新状态。您可以通过多种方式实现这一目标。以下示例使用广播将信息从服务发送到 activity。

该服务会声明一个函数来广播新状态。此函数接受一个操作字符串，该字符串在广播到系统之前会传递给 Intent 对象。

Kotlin

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

Java

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

广播函数就位后会在 BluetoothGattCallback 中使用，用于发送有关与 GATT 服务器的连接状态的信息。常量和服务的当前连接状态在表示 Intent 操作的服务中声明。

Kotlin

class BluetoothLeService : Service() {

    private var connectionState = STATE_DISCONNECTED

    private val bluetoothGattCallback: BluetoothGattCallback = object : BluetoothGattCallback() {
        override fun onConnectionStateChange(gatt: BluetoothGatt, status: Int, newState: Int) {
            if (newState == BluetoothProfile.STATE_CONNECTED) {
                // successfully connected to the GATT Server
                connectionState = STATE_CONNECTED
                broadcastUpdate(ACTION_GATT_CONNECTED)
            } else if (newState == BluetoothProfile.STATE_DISCONNECTED) {
                // disconnected from the GATT Server
                connectionState = STATE_DISCONNECTED
                broadcastUpdate(ACTION_GATT_DISCONNECTED)
            }
        }
    }

    ...

    companion object {
        const val ACTION_GATT_CONNECTED =
            "com.example.bluetooth.le.ACTION_GATT_CONNECTED"
        const val ACTION_GATT_DISCONNECTED =
            "com.example.bluetooth.le.ACTION_GATT_DISCONNECTED"

        private const val STATE_DISCONNECTED = 0
        private const val STATE_CONNECTED = 2

    }
}

Java


class BluetoothLeService extends Service {

    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";

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

    private int connectionState;
    ...

    private final BluetoothGattCallback bluetoothGattCallback = new BluetoothGattCallback() {
        @Override
        public void onConnectionStateChange(BluetoothGatt gatt, int status, int newState) {
            if (newState == BluetoothProfile.STATE_CONNECTED) {
                // successfully connected to the GATT Server
                connectionState = STATE_CONNECTED;
                broadcastUpdate(ACTION_GATT_CONNECTED);
            } else if (newState == BluetoothProfile.STATE_DISCONNECTED) {
                // disconnected from the GATT Server
                connectionState = STATE_DISCONNECTED;
                broadcastUpdate(ACTION_GATT_DISCONNECTED);
            }
        }
    };

    …
}

在活动中监听更新

服务广播连接更新后，activity 需要实现 BroadcastReceiver。在设置 activity 时注册此接收器，并在 activity 离开屏幕时取消注册此接收器。通过监听来自该服务的事件，activity 能够根据与 BLE 设备的当前连接状态更新界面。

Kotlin

class DeviceControlActivity : AppCompatActivity() {

...

    private val gattUpdateReceiver: BroadcastReceiver = object : BroadcastReceiver() {
        override fun onReceive(context: Context, intent: Intent) {
            when (intent.action) {
                BluetoothLeService.ACTION_GATT_CONNECTED -> {
                    connected = true
                    updateConnectionState(R.string.connected)
                }
                BluetoothLeService.ACTION_GATT_DISCONNECTED -> {
                    connected = false
                    updateConnectionState(R.string.disconnected)
                }
            }
        }
    }

    override fun onResume() {
        super.onResume()
        registerReceiver(gattUpdateReceiver, makeGattUpdateIntentFilter())
        if (bluetoothService != null) {
            val result = bluetoothService!!.connect(deviceAddress)
            Log.d(DeviceControlsActivity.TAG, "Connect request result=$result")
        }
    }

    override fun onPause() {
        super.onPause()
        unregisterReceiver(gattUpdateReceiver)
    }

    private fun makeGattUpdateIntentFilter(): IntentFilter? {
        return IntentFilter().apply {
            addAction(BluetoothLeService.ACTION_GATT_CONNECTED)
            addAction(BluetoothLeService.ACTION_GATT_DISCONNECTED)
        }
    }
}

Java

class DeviceControlsActivity extends AppCompatActivity {

...

    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);
            } else if (BluetoothLeService.ACTION_GATT_DISCONNECTED.equals(action)) {
                connected = false;
                updateConnectionState(R.string.disconnected);
            }
        }
    };

    @Override
    protected void onResume() {
        super.onResume();

        registerReceiver(gattUpdateReceiver, makeGattUpdateIntentFilter());
        if (bluetoothService != null) {
            final boolean result = bluetoothService.connect(deviceAddress);
            Log.d(TAG, "Connect request result=" + result);
        }
    }

    @Override
    protected void onPause() {
        super.onPause();
        unregisterReceiver(gattUpdateReceiver);
    }

    private static IntentFilter makeGattUpdateIntentFilter() {
        final IntentFilter intentFilter = new IntentFilter();
        intentFilter.addAction(BluetoothLeService.ACTION_GATT_CONNECTED);
        intentFilter.addAction(BluetoothLeService.ACTION_GATT_DISCONNECTED);
        return intentFilter;
    }
}

在传输 BLE 数据中，BroadcastReceiver 还可用于传达服务发现以及来自设备的特征数据。

关闭 GATT 连接

处理蓝牙连接时，一个重要的步骤是在处理完成后关闭连接。为此，请对 BluetoothGatt 对象调用 close() 函数。在以下示例中，服务保存对 BluetoothGatt 的引用。当 activity 与服务取消绑定时，系统会关闭连接，以避免消耗设备电池电量。

Kotlin

class BluetoothLeService : Service() {

...

    override fun onUnbind(intent: Intent?): Boolean {
        close()
        return super.onUnbind(intent)
    }

    private fun close() {
        bluetoothGatt?.let { gatt ->
            gatt.close()
            bluetoothGatt = null
        }
    }
}

Java

class BluetoothLeService extends Service {

...

      @Override
      public boolean onUnbind(Intent intent) {
          close();
          return super.onUnbind(intent);
      }

      private void close() {
          if (bluetoothGatt == null) {
              Return;
          }
          bluetoothGatt.close();
          bluetoothGatt = null;
      }
}