UWP Bluetooth LE InvalidCastException

Question

i want to connect the myo wristband to the hololens. This is the end goal, but I am anyway but close to that :-/

The idea is to set up a Bluetooth LE Connection with UWP. I wanted to do this, as explanined in this Microsoft Document

The search for the devices workes fine, but when I try to connect to a device, this line (Point "Connecting to the device" ): GattDeviceServicesResult result = await device.GetGattServicesAsync();

raises the error:

System.InvalidCastException: "Unable to cast object of type 'Windows.Devices.Bluetooth.BluetoothLEDevice' to type 'Windows.Devices.Bluetooth.IBluetoothLEDevice3'."

I have no idea what the IBluetoothLEDevice3 has to do there :-) I was not able to find a solution for this on the microsoft documentation or the internet :-/

I work on Visual Studio 2017, build for Windows 10 (15063) and Bluetooth is enabled in the manifest.

This is my code so fare. I added only one thing and that is the Task. I wanted to make sure, that the BluetoothLEDDevice is not null or anything, since it is not synchron. Without its not working either.

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Runtime.InteropServices.WindowsRuntime;
using Windows.Foundation;
using Windows.Foundation.Collections;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;
using Windows.UI.Xaml.Controls.Primitives;
using Windows.UI.Xaml.Data;
using Windows.UI.Xaml.Input;
using Windows.UI.Xaml.Media;
using Windows.UI.Xaml.Navigation;
using System.Diagnostics;
using Windows.Devices.Enumeration;
using Windows.Devices.Bluetooth;
using Windows.Devices.Bluetooth.GenericAttributeProfile;
using System.Threading.Tasks;
using Windows.Devices.Bluetooth.Advertisement;


// Die Elementvorlage "Leere Seite" wird unter https://go.microsoft.com/fwlink/?LinkId=402352&clcid=0x407 dokumentiert.

namespace Bluetooth17
{
    /// <summary>
    /// Eine leere Seite, die eigenständig verwendet oder zu der innerhalb eines Rahmens navigiert werden kann.
    /// </summary>
    public sealed partial class MainPage : Page    
    {


        public MainPage()
        {
            this.InitializeComponent();

            blue();

        }



        void blue()
        {
            // Query for extra properties you want returned
            string[] requestedProperties = { "System.Devices.Aep.DeviceAddress", "System.Devices.Aep.IsConnected" };

            DeviceWatcher deviceWatcher =
                        DeviceInformation.CreateWatcher(
                                BluetoothLEDevice.GetDeviceSelectorFromPairingState(false),
                                requestedProperties,
                                DeviceInformationKind.AssociationEndpoint);

            // Register event handlers before starting the watcher.
            // Added, Updated and Removed are required to get all nearby devices
            deviceWatcher.Added += DeviceWatcher_Added;
            deviceWatcher.Updated += DeviceWatcher_Updated;
            deviceWatcher.Removed += DeviceWatcher_Removed;

            // EnumerationCompleted and Stopped are optional to implement.
            deviceWatcher.EnumerationCompleted += DeviceWatcher_EnumerationCompleted;
            deviceWatcher.Stopped += DeviceWatcher_Stopped;

            // Start the watcher.
            deviceWatcher.Start();
        }

        private void DeviceWatcher_Stopped(DeviceWatcher sender, object args)
        {
            Debug.WriteLine("Stopped");
        }

        private void DeviceWatcher_EnumerationCompleted(DeviceWatcher sender, object args)
        {
            Debug.WriteLine("Enum complete");
        }

        private void DeviceWatcher_Removed(DeviceWatcher sender, DeviceInformationUpdate args)
        {
            Debug.WriteLine(args.Id + "  Removed");
        }

        private void DeviceWatcher_Updated(DeviceWatcher sender, DeviceInformationUpdate args)
        {
            Debug.WriteLine(args.Id + " Update");
        }

        private void DeviceWatcher_Added(DeviceWatcher sender, DeviceInformation args)
        {
            Debug.WriteLine(args.Id + "       " + args.Name);

            if (args.Name.Equals("Myo"))
            {
                Debug.WriteLine("Try to connect to Myo");
                getServices(args);
            }
        }

        async Task<BluetoothLEDevice> ConnectDevice(DeviceInformation deviceInfo)
        {
            Debug.WriteLine("Asyc");
            // Note: BluetoothLEDevice.FromIdAsync must be called from a UI thread because it may prompt for consent.
             return await BluetoothLEDevice.FromIdAsync(deviceInfo.Id);


        }


        async void getServices(DeviceInformation deviceInfo)
           {

            Task<BluetoothLEDevice> task = ConnectDevice(deviceInfo);

            task.Wait();

            BluetoothLEDevice device = task.Result;

            GattDeviceServicesResult result = await device.GetGattServicesAsync();

            if (result.Status == GattCommunicationStatus.Success)
            {
                var services = result.Services;
                // ...
            }

        }
    }
}

Thank you

Answer 1

If you target your application to Build 15063 and you know the device you are connecting to than just use:

device = await BluetoothLEDevice.FromBluetoothAddressAsync(blueToothAddress);  

This is much more stable than your code and no need for device watcher. Here is an example that works for my device(not a MIO but a HM10) :

using System;
using System.Diagnostics;
using Windows.Devices.Bluetooth;
using Windows.Devices.Bluetooth.GenericAttributeProfile;
using Windows.UI.Xaml.Controls;

namespace App1
{    
   public sealed partial class MainPage : Page
   {
      private BluetoothLEDevice device;
      GattDeviceServicesResult serviceResult = null;
      public MainPage()
      {
         this.InitializeComponent();
         StartDevice();
      }

      private async void StartDevice()
      {
         //To get your blueToothAddress add: ulong blueToothAddress = device.BluetoothAddress to your old code.
         ulong blueToothAddress = 88396936323791; //fill in your device address!!
         device = await BluetoothLEDevice.FromBluetoothAddressAsync(blueToothAddress);         
         if (device != null)
         {
            string deviceName = device.DeviceInformation.Name;
            Debug.WriteLine(deviceName);
            int servicesCount = 3;//Fill in the amount of services from your device!!
            int tryCount = 0;
            bool connected = false;
            while (!connected)//This is to make sure all services are found.
            {
               tryCount++;
               serviceResult = await device.GetGattServicesAsync();

               if (serviceResult.Status == GattCommunicationStatus.Success && serviceResult.Services.Count >= servicesCount)
               {
                  connected = true;
                  Debug.WriteLine("Connected in " + tryCount + " tries");
               }
               if (tryCount > 5)//make this larger if faild
               {
                  Debug.WriteLine("Failed to connect to device ");
                  return;
               }
            }
         }
      }
   }
}