Xamarin Android的藍牙LE特性

Question

我正在嘗試從Xamarin Android應用程序讀取Bluetooth LE特性。

m_characteristicReady = new SemaphoreSlim(1);
m_characteristicChanged = new SemaphoreSlim(1);



 public async Task<BluetoothGattCharacteristic> GetCharecteristic(int timeout,BluetoothGattCharacteristic characteristic)
        {
            EnableCharacteristicNotification(characteristic);
            //Once notifications are enabled for a characteristic, 
            //an onCharacteristicChanged() callback is triggered if the characteristic changes on the remote device:
            m_characteristicChanged.Wait();

            //We serialize all requests and timeout only on requests themself cand not their predesesors
            m_characteristicReady.Wait();
           //todo check result ???
            m_gatt.ReadCharacteristic(characteristic);
            if (await m_characteristicReady.WaitAsync(timeout) == true || 
                await m_characteristicChanged.WaitAsync(timeout) == true)
            {
                m_characteristicChanged.Release();
                m_characteristicReady.Release();
                return m_characteristic;
            }
            return null;
        }

    public override void OnCharacteristicRead(BluetoothGatt gatt, BluetoothGattCharacteristic characteristic, [Android.Runtime.GeneratedEnum] GattStatus status)
    {
        m_characteristic = characteristic;
        m_characteristicReady.Release();
    }

    public override void OnCharacteristicChanged(BluetoothGatt gatt, BluetoothGattCharacteristic characteristic)
    {
        m_characteristic = characteristic;
        m_characteristicChanged.Release();
    }

我的問題在我的public async Task<BluetoothGattCharacteristic> GetCharecteristic(int timeout,BluetoothGattCharacteristic characteristic)函數內部

1） is there a possiblity of a deadlock?

2） Is there a way for me to check if the attribute is (notifiable) before enabling notification

Answer 1

有沒有可能發生僵局？

如果兩者都為m_gatt.readCharacteristic(gattCharacteristic); 和m_gatt.writeCharacteristic(gattCharacteristic); 方法被異步調用，這可能導致死鎖。 因為您可以使用兩個SemaphoreSlim同時更改m_characteristic 。 使用一個SemaphoreSlim可以解決死鎖，如下代碼：

    public async Task<BluetoothGattCharacteristic> GetCharecteristic(int timeout, BluetoothGattCharacteristic characteristic)
    {
        EnableCharacteristicNotification(characteristic);            
        m_gatt.ReadCharacteristic(characteristic);                 
        return m_characteristic;
    }

    public override void OnCharacteristicRead(BluetoothGatt gatt, BluetoothGattCharacteristic characteristic, [Android.Runtime.GeneratedEnum] GattStatus status)
    {
        m_SemaphoreSlim.Wait();
        m_characteristic = characteristic;
        m_SemaphoreSlim.Release();
    }

    public override void OnCharacteristicChanged(BluetoothGatt gatt, BluetoothGattCharacteristic characteristic)
    {
        m_SemaphoreSlim.Wait();
        m_characteristic = characteristic;
        m_SemaphoreSlim.Release();
    }

在啟用通知之前，有沒有辦法讓我檢查屬性是否（可通知）

您可以使用setCharacteristicNotification的返回值作為以下代碼，以檢查該屬性是否為（可通知的）：

       boolean isEnableNotification = mBluetoothGatt.setCharacteristicNotification(characteristic, enabled);
       if (isEnableNotification)
       {
       //.....
       }

但是，在調用setCharacteristicNotification之前，沒有方法可以檢查該屬性是否為（可通知的）。