来自Xamarin的蓝牙LE特征Android

Question

我想从Xamarin Android应用程序中读取蓝牙LE特征。

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(); 
    } 

我的问题是我的public async Task<BluetoothGattCharacteristic> GetCharecteristic(int timeout,BluetoothGattCharacteristic characteristic) 功能

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

有死锁的方法可行里面？

如果同时调用m_gatt.readCharacteristic(gattCharacteristic);和m_gatt.writeCharacteristic(gattCharacteristic);方法，则可能导致死锁。因为您可以使用两个SemaphoreSlim同时更改m_characteristic。使用一个SemaphoreSlim可以解决死锁如下面的代码：

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(); 
    } 

有没有为我检查，如果该属性是（法定）启用通知

可以使用返回之前的方式检查的setCharacteristicNotification值如下的代码，如果该属性是（法定）：

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

但你打电话之前setCharacte ristic通知没有方法检查属性是否（通知）。