C＃Windows 10蓝牙LE无法连接到服务器

Question

I'm developing ac# desktop api with forms where I want to receive ACC data from a BLE server und display them in a chart. So I'm running in a connection problem and I can't find any solution. I can find my LE server Device with the watcher.

DevicePairingResult dpr = await device.DeviceInformation.Pairing.PairAsync(DevicePairingProtectionLevel.Encryption);

returns me "AlreadyPaired"

But when I do

device = await BluetoothLEDevice.FromBluetoothAddressAsync(bluetoothAddress: eventArgs.BluetoothAddress);
mGattService = device.GetGattService(MotionService_GUID);
mCharacteristic = mGattService.GetCharacteristics(ACC_Characteristic_GUID)[0];

and then

var con = device.ConnectionStatus;

I receive "Disconnected" in con.

I am bound with de device on windows( I searched for it in Windows and entered the Code) but I am not connected(based on the Status in the windows info center). I've read in another Thread in the windows c# developer page that it should not be necessary anymore to pair the device manually.

I'm pretty shure that the rest of my code works because sometimes I can get a connection( pretty confusing for me) and see the right Data in my chart. Right now I just want to reach a stable connection before changing other part of my code. Anyone any idea how to solve this? Thx medTech

Edit: Here is part of the Code:

Scanning for BLE

private void button1_Click(object sender, EventArgs e)
        {

            // Create Bluetooth Listener
            var watcher = new BluetoothLEAdvertisementWatcher();

            watcher.ScanningMode = BluetoothLEScanningMode.Active;

            // Register callback for when we see an advertisements
            watcher.Received += OnAdvertisementReceivedAsync;

            // Wait 5 seconds to make sure the device is really out of range
            watcher.SignalStrengthFilter.OutOfRangeTimeout = TimeSpan.FromMilliseconds(5000);
            watcher.SignalStrengthFilter.SamplingInterval = TimeSpan.FromMilliseconds(2000);

            // Starting watching for advertisements
            watcher.Start();
        }

Connect to Server:

private async void OnAdvertisementReceivedAsync(BluetoothLEAdvertisementWatcher watcher, BluetoothLEAdvertisementReceivedEventArgs eventArgs)
        {

            // Filter for specific Device
            if (eventArgs.Advertisement.LocalName == "MYDEVICE")
            {
                watcher.Stop();

                var MotionService_GUID = new Guid("00002000-0000-1000-8000-00805F9B34FB");
                var ACC_Characteristic_GUID = new Guid("00002001-0000-1000-8000-00805F9B34FB");


                    device = await BluetoothLEDevice.FromBluetoothAddressAsync(bluetoothAddress: eventArgs.BluetoothAddress);
                    DevicePairingResult dpr = await device.DeviceInformation.Pairing.PairAsync(DevicePairingProtectionLevel.Encryption);
                    mGattService = device.GetGattService(MotionService_GUID);


                    mCharacteristic = mGattService.GetCharacteristics(ACC_Characteristic_GUID)[0];

                    GattDeviceServicesResult result = await device.GetGattServicesAsync();


                    GattCommunicationStatus status1 = await ReadFromCharacteristicAsync(mCharacteristic);

                    var con = device.ConnectionStatus;
                    while (status1 == GattCommunicationStatus.Success)
                    {
                        try
                        {
                            status1 = await ReadFromCharacteristicAsync(mCharacteristic);
                        }
                        catch
                        {
                            Console.WriteLine("ERROR");
                            status1 = GattCommunicationStatus.Unreachable;

                        }
                    }

            }
            }

Read from Characteristic:

async Task ReadFromCharacteristicAsync(GattCharacteristic mCharacteristic) {

        GattReadResult readResult = await mCharacteristic.ReadValueAsync(BluetoothCacheMode.Uncached);

        if (readResult.Status == GattCommunicationStatus.Success)
        {
            byte[] data = new byte[readResult.Value.Length];
            DataReader.FromBuffer(readResult.Value).ReadBytes(data);
            if (chart1.IsHandleCreated)
            {
                this.Invoke((MethodInvoker)delegate { updateChart(data); });
            }

            return readResult.Status;
        }
        return readResult.Status;
    }

Terminate Connection

 private async Task<bool> ClearBluetoothLEDeviceAsync()
        {

            mCharacteristic.Service.Dispose();
            mGattService.Dispose();
            await device.DeviceInformation.Pairing.UnpairAsync();
            device?.Dispose();
            device = null;
            GC.Collect();
            return true;
        }

SO now when I connect the first time to the Server, I only receive zeros which shows me that the there might be a authentication Error. After that I always receive this Error: "System.ArgumentException" in mscorlib.dll with a notification that there is noch executable Code left because all Threads are doing some asynchronous stuff. This Error gets thrown when I try to read from the Characteristic. I never coded in c# before so I am not shure if there is an error in my asynchronous part oder the communication part. Thanks you

Answer 1

Pairing is not the same as connecting! I really advise using the BLE-advertisementWatcher to select and connect to your device. The reason is that many BLE-devices don't save their pairing status. In windows device-watcher once paired, the device stays paired even if it is switched off or out of reach. Also many times the connection status is kept, unless the device is unpaired and disposed in code or removed in windows settings.

All BLE-devices that I know of start advertising as soon as there is no connection for some time. This time depends on the device, but most of the time within seconds.

So don't pair but just connect if the device is advertising.