Android BLE中心设备的onCharacteristicChanged()方法没有回调

描述：当设备为 Indication 模式时，设备的值有变化时会主动返回给App，App在 onCharacteristicChanged() 方法中能收到返回的值。

Indication： 从机会先向主机发送一条通知，主机接收到通知后去读取从机数据

Notification：从机直接发送给主机数据

问题：在App中通过如下代码注册监听，注册成功后就能接收到设备主动反馈的值了。然而以下代码执行后依旧收不到反馈。但是对设备的读写都是可行的，并且iOS端可以接收到通知。

bluetoothGatt.setCharacteristicNotification(characteristic, true)

解决： 当上面的方法执行返回true后，还要执行如下的代码才能注册成功。

for(BluetoothGattDescriptor dp: characteristic.getDescriptors()){
if (dp != null) {
if ((characteristic.getProperties() & BluetoothGattCharacteristic.PROPERTY_NOTIFY) != 0) {
dp.setValue(BluetoothGattDescriptor.ENABLE_NOTIFICATION_VALUE);
} else if ((characteristic.getProperties() & BluetoothGattCharacteristic.PROPERTY_INDICATE) != 0) {
dp.setValue(BluetoothGattDescriptor.ENABLE_INDICATION_VALUE);
}
gatt.writeDescriptor(dp);
}
}

完整的代码如下：

public boolean enableNotification(BluetoothGatt gatt, UUID serviceUUID, UUID characteristicUUID) {
boolean success = false;
BluetoothGattService service = gatt.getService(serviceUUID);
if (service != null) {
BluetoothGattCharacteristic characteristic = findNotifyCharacteristic(service, characteristicUUID);
if (characteristic != null) {
success = gatt.setCharacteristicNotification(characteristic, true);
if (success) {
// 来源：http://stackoverflow.com/questions/38045294/oncharacteristicchanged-not-called-with-ble
for(BluetoothGattDescriptor dp: characteristic.getDescriptors()){
if (dp != null) {
if ((characteristic.getProperties() & BluetoothGattCharacteristic.PROPERTY_NOTIFY) != 0) {
dp.setValue(BluetoothGattDescriptor.ENABLE_NOTIFICATION_VALUE);
} else if ((characteristic.getProperties() & BluetoothGattCharacteristic.PROPERTY_INDICATE) != 0) {
dp.setValue(BluetoothGattDescriptor.ENABLE_INDICATION_VALUE);
}
gatt.writeDescriptor(dp);
}
}}
}
}
return success;
}

private BluetoothGattCharacteristic findNotifyCharacteristic(BluetoothGattService service, UUID characteristicUUID) {
BluetoothGattCharacteristic characteristic = null;
List<BluetoothGattCharacteristic> characteristics = service.getCharacteristics();
for (BluetoothGattCharacteristic c : characteristics) {
if ((c.getProperties() & BluetoothGattCharacteristic.PROPERTY_NOTIFY) != 0
&& characteristicUUID.equals(c.getUuid())) {
characteristic = c;
break;
}
}
if (characteristic != null)
return characteristic;
for (BluetoothGattCharacteristic c : characteristics) {
if ((c.getProperties() & BluetoothGattCharacteristic.PROPERTY_INDICATE) != 0
&& characteristicUUID.equals(c.getUuid())) {
characteristic = c;
break;
}
}
return characteristic;
}