xamarin - 如何在 Xamarin/Android 上启用多个 BLE 特征通知？

Question

我正在尝试使用 Xamarin/Android 为多个 BLE 特性启用通知，但似乎无法这样做。如果我尝试一次启用多个，该应用程序似乎停止接收任何 BLE 事件。

任何人都可以使用 Tamarin/Android 确认这是否可行。我们有一个原生 iOS 应用程序，可以在启用多个通知的情况下正常工作。我们使用的基本步骤如下:

扫描设备

连接设备

发现服务

对于每个发现的服务，遍历特征并启用所需的特征

处理BLE回调中的每个异步回调事件

每当我们尝试针对多个特征启用通知时，我们都不会再收到任何事件。

我也找不到任何启用多个特性的示例。

我希望我在这里只是错过了使用 Xamarin/Android API 的一些基本知识。

public override void OnServicesDiscovered (BluetoothGatt gatt, GattStatus status)
{
    base.OnServicesDiscovered (gatt, status);
    foreach (BluetoothGattService service in gatt.Services) {
        string uuid = service.Uuid.ToString ().ToUpper();
        if (uuid.Equals (BLEServices.HRService.ToUpper())) {
            _Adap.LogMessage ("HRService discovered");
            foreach(BluetoothGattCharacteristic characteristic in service.Characteristics) {
                string c_uuid = characteristic.Uuid.ToString ().ToUpper ();
                _Adap.LogMessage (" HRCharacteristic: " + c_uuid);

                if (c_uuid.Equals(_Adap.useCharacteristic.ToUpper())) {
                    _Adap.LogMessage ("  enabling HRCharacteristic");
                    gatt.SetCharacteristicNotification(characteristic, true);
                    BluetoothGattDescriptor descriptor = new BluetoothGattDescriptor (Java.Util.UUID.FromString (BLEServices.CLIENT_CHARACTERISTIC_CONFIG), GattDescriptorPermission.Write | GattDescriptorPermission.Read);
                    characteristic.AddDescriptor (descriptor);
                    descriptor.SetValue (BluetoothGattDescriptor.EnableNotificationValue.ToArray ());
                    gatt.WriteDescriptor (descriptor);
                    _Adap.StartTimer ();
                }
            }

        } else if (uuid.Equals (BLEServices.BatteryService.ToUpper())) {
            _Adap.LogMessage ("BatteryService discovered");
            foreach (BluetoothGattCharacteristic characteristic in service.Characteristics) {
                string c_uuid = characteristic.Uuid.ToString ().ToUpper ();
                _Adap.LogMessage (" BatteryService: " + c_uuid);

                if (c_uuid.Equals (_Adap.useCharacteristic.ToUpper ())) {
                    _Adap.LogMessage ("  reading batteryCharacteristic");
                    // This may only be reported when the battery level changes so get the level first by doing a read
                    gatt.ReadCharacteristic (characteristic);

                    //gatt.SetCharacteristicNotification (characteristic, true);
                    //BluetoothGattDescriptor descriptor = new BluetoothGattDescriptor (Java.Util.UUID.FromString (BLEServices.CLIENT_CHARACTERISTIC_CONFIG), GattDescriptorPermission.Write | GattDescriptorPermission.Read);
                    //characteristic.AddDescriptor (descriptor);
                    //descriptor.SetValue (BluetoothGattDescriptor.EnableNotificationValue.ToArray ());
                    //gatt.WriteDescriptor (descriptor);
                }
            }
        } else if (uuid.Equals (BLEServices.DeviceInfoService.ToUpper())) {
            _Adap.LogMessage ("DeviceInfoService discovered");
            foreach (BluetoothGattCharacteristic characteristic in service.Characteristics) {
                string c_uuid = characteristic.Uuid.ToString ().ToUpper ();
                _Adap.LogMessage (" DeviceInfoService: " + c_uuid);
                if (c_uuid.Equals (BLEServices.kModelNumberCharacteristicUuidString.ToUpper ())) {
                    //gatt.ReadCharacteristic (characteristic);
                }
            }
        } else if (uuid.Equals (BLEServices.kHxM2CustomServiceUuidString.ToUpper())) {
            _Adap.LogMessage ("HxM2CustomService discovered");
            foreach (BluetoothGattCharacteristic characteristic in service.Characteristics) {
                string c_uuid = characteristic.Uuid.ToString ().ToUpper ();
                _Adap.LogMessage (" HxM2CustomCharacteristic: " + c_uuid);

                if (c_uuid.Equals (_Adap.useCharacteristic.ToUpper ())) {
                    _Adap.LogMessage ("  enabling HxM2 characteristic: "+_Adap.useCharacteristic);
                    gatt.SetCharacteristicNotification (characteristic, true);
                    BluetoothGattDescriptor descriptor = new BluetoothGattDescriptor (Java.Util.UUID.FromString (BLEServices.CLIENT_CHARACTERISTIC_CONFIG), GattDescriptorPermission.Write | GattDescriptorPermission.Read);
                    characteristic.AddDescriptor (descriptor);
                    descriptor.SetValue (BluetoothGattDescriptor.EnableNotificationValue.ToArray ());
                    gatt.WriteDescriptor (descriptor);
                    // Start a timer to make sure that we can recover if we never receive any data from the device
                    _Adap.StartTimer ();
                }

            }
        } else {
            _Adap.LogMessage ("Unknown Service "+uuid+" discovered");
        }
    }
}

谁能解释以下几行的用途

BluetoothGattDescriptor descriptor = new BluetoothGattDescriptor (Java.Util.UUID.FromString (BLEServices.CLIENT_CHARACTERISTIC_CONFIG), GattDescriptorPermission.Write | GattDescriptorPermission.Read);
characteristic.AddDescriptor (descriptor);
descriptor.SetValue (BluetoothGattDescriptor.EnableNotificationValue.ToArray ());
gatt.WriteDescriptor (descriptor);

Answer 1

除了您找到的解决方案:请注意，您无法聆听无限数量的特征。 android 源代码中的最大值被限制为 BTA_GATTC_NOTIF_REG_MAX .

安卓 >= 4.3: 4
http://androidxref.com/4.3_r2.1/xref/external/bluetooth/bluedroid/bta/gatt/bta_gattc_int.h#301

安卓 >= 4.4:7 http://androidxref.com/4.4.4_r1/xref/external/bluetooth/bluedroid/bta/gatt/bta_gattc_int.h#333

安卓 >= 5.0:15 http://androidxref.com/5.0.0_r2/xref/external/bluetooth/bluedroid/bta/gatt/bta_gattc_int.h#345

因此，您的应用不应该依赖于您支持的最低 Android 版本的最大通知特性数量。