写入操作不会以 xamarin 形式更新 iOS 的特征值

Question

我正在使用 xamarin 表单创建一个BLE 应用程序。 在 Android 中一切正常，我能够读写 GATT 特性。 在 iOS 中，我能够成功读取，但写入操作不会更新特性值。 写操作没有错误，正在执行，但特征值没有变化。 我尝试了名为light blue 的iOS 本机应用程序，其工作正常，特征值已更新，我仅在 Xamarin 表单应用程序中遇到问题。 这是我的代码

 private async Task<string> ProcessDeviceInformationService(IService deviceInfoService)
        {
            try
            {
               await adapter.ConnectToDeviceAsync(device);
                var sb = new StringBuilder("Getting information from Device Information service: \n");
                 var characteristics =  deviceInfoService.GetCharacteristicsAsync();
                var characteristic = await deviceInfoService.GetCharacteristicAsync(Guid.Parse("00002a2b-0000-1000-8000-00805F9B34FB"));
                
                try
                {
                    
                    if (characteristic != null)
                    {
                        var sbnew = new StringBuilder("BLE Characteristics\n");
                        byte[] senddata = Encoding.UTF8.GetBytes(string.IsNullOrEmpty(SendMessageLabel.Text) ? "12" : SendMessageLabel.Text);

 

                       
                    
                                                    
                                                 
                        
                        characteristic.ValueUpdated += (o, args) =>
                          {
                        
                         var bytes = characteristic.Value;
                                                 };
                                               await characteristic.WriteAsync(senddata);

 

                                                                                                     
                      

 

                        string str = Encoding.UTF8.GetString(senddata);

 

                  

 

                        sbnew.AppendLine($"Characteristics found on this device: {string.Join(", ", str.ToString())}");
                            CharactericsLabel.Text = sbnew.ToString();
                        

 


                    }
                }
                catch (Exception ex)
                {
                    //return ex.Message;
                    DisplayAlert("Notice", ex.Message.ToString(), "OK");

 

                }

我尝试了延迟，我也尝试在没有外围设备响应的情况下进行写入，但它不起作用。 这是我的外围代码

 // Current Time characteristic
BluetoothGattCharacteristic currentTime = new BluetoothGattCharacteristic(CURRENT_TIME,
        //Read-only characteristic, supports notifications
        BluetoothGattCharacteristic.PROPERTY_READ | BluetoothGattCharacteristic.PROPERTY_NOTIFY | BluetoothGattCharacteristic.PROPERTY_WRITE_NO_RESPONSE,
        BluetoothGattCharacteristic.PERMISSION_READ | BluetoothGattCharacteristic.PROPERTY_WRITE);
BluetoothGattDescriptor configDescriptor = new BluetoothGattDescriptor(CLIENT_CONFIG,
        //Read/write descriptor
        BluetoothGattDescriptor.PERMISSION_READ | BluetoothGattDescriptor.PERMISSION_WRITE);
currentTime.addDescriptor(configDescriptor);
// Local Time Information characteristic
BluetoothGattCharacteristic localTime = new BluetoothGattCharacteristic(LOCAL_TIME_INFO,
        //Read-only characteristic
        BluetoothGattCharacteristic.PROPERTY_READ,
        BluetoothGattCharacteristic.PERMISSION_READ);
BluetoothGattCharacteristic sampleText = new BluetoothGattCharacteristic sampleText = new BluetoothGattCharacteristic(SAMPLE_TEXT,
        //Read-only characteristic
        BluetoothGattCharacteristic.PROPERTY_WRITE_NO_RESPONSE | BluetoothGattCharacteristic.PROPERTY_READ | BluetoothGattCharacteristic.PROPERTY_NOTIFY,
        BluetoothGattCharacteristic.PERMISSION_WRITE | BluetoothGattCharacteristic.PERMISSION_READ);

我不知道如何解决任何建议。我什至尝试了信号量，但它没有帮助，正如您在我的代码中看到的那样

private static async Task<string> WriteAndWaitForResponseAsync(
    ICharacteristic characteristic,
    byte[] senddata)
        {
            var semaphore = new SemaphoreSlim(0, 1);
            string result = null;

            characteristic.ValueUpdated += (o, args) =>
            {
                var bytes = characteristic.Value;

                result = Encoding.UTF8.GetString(bytes);  // Note I don't know if this is your intended behaviour with the values you get back, you can decide what to actually do with the response.
                                                          // Notify a value has been received.
                semaphore.Release();
            };

            await characteristic.WriteAsync(senddata,new CancellationToken(true)).ConfigureAwait(false);

            // Wait until we receive a notification.
            await semaphore.WaitAsync(); // I strongly suggest you look in to CancellationTokens but I am not going in to that now.
           
            return result;
        }

Answer 1

我怀疑线程是这里问题的一部分，您订阅了该事件，调用WriteAsync但最终在收到数据/事件之前离开了该方法。 我建议您需要在收到数据之前尝试阻止该方法离开。

尝试类似：

private static async Task<string> WriteAndWaitForResponseAsync(
    ICharacteristic characteristic,
    byte[] senddata)
{
    var semaphore = new SemaphoreSlim(0, 1);
    string result = null;

    characteristic.ValueUpdated += (o, args) =>
    {
        // Make sure you read from the new value in event not the existing characteristic.
        var bytes = args.Characteristic.Value;

        result = Encoding.UTF8.GetString(bytes);  // Note I don't know if this is your intended behaviour with the values you get back, you can decide what to actually do with the response.
        // Notify a value has been received.
        semaphore.Release();
    };
    
    await characteristic.WriteAsync(senddata);

    // Wait until we receive a notification.
    await semaphore.WaitAsync(); // I strongly suggest you look in to CancellationTokens but I am not going in to that now.

    return result;
}

然后，您可以从当前的方法中调用此方法，例如：

string str = await WriteAndWaitForResponseAsync(characteristic, senddata);