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UWP Bluetooth LE InvalidCastException

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

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;
}
}
}
}
}
}

C# UDP Chat receive no message

I try to write a UDP-Chat in C#.
I have some unexpected behavoir in my Chat Programm, when I start the programm on two different machines connected to the same Network. At the first mashine the programm works fine it can send and recive messages properly, but on the second machine it can just send messages but it can't recive them.
I testet this with a 3rd mashine too(a VM with a bridged networkinterface), but with the same result, it just can send messages without recieving.
is there a error in my code or is it a desing error?
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Shapes;
using System.Net.Sockets;
using System.Net;
using System.Diagnostics;
using System.Threading;
using System.Net.NetworkInformation;
using System.ComponentModel;
using System.Data;
namespace CScharpChat
{
/// <summary>
/// Interaktionslogik für Chat_window.xaml
/// </summary>
public partial class Chat_window : Window
{
string name = "testuser";
UdpClient receiveClient = new UdpClient(1800);
IPEndPoint receiveEndPint = new IPEndPoint(IPAddress.Any, 0);
public Chat_window(string name)
{
this.name = name;
fileWriter("Chat started", false); // write the initial start date in the errorfile
InitializeComponent();
Message_Load(); // starts the listen server theread
}
private void Message_Load()
{
lb_chat.Items.Add(name + " Joined the room...");
Thread rec = new Thread(ReceiveMessageFn);
rec.Start();
}
private void ReceiveMessageFn()
{
try
{
while (true)
{
Byte[] receve = receiveClient.Receive(ref receiveEndPint);
string message = Encoding.UTF8.GetString(receve);
if (message == name + " logged out...")
{
break;
}
else
{
if (message.Contains(name + " says >>"))
{
message = message.Replace(name + " says >>", "Me says >>");
}
ShowMessage(message);
}
}
//Thread.CurrentThread.Abort();
//Application.Current.Shutdown();
}
catch (Exception e)
{
//errorHandler(e);
}
}
private void ShowMessage(string message)
{
if (lb_chat.Dispatcher.CheckAccess())
{
lb_chat.Items.Add(message);// add Item to list-box
lb_chat.ScrollIntoView(lb_chat.Items[lb_chat.Items.Count - 1]);// scroll down to current Item
lb_chat.UpdateLayout();
}
else {
lb_chat.Dispatcher.BeginInvoke(
new Action<string>(ShowMessage), message); // if list-box is not access able get access
return;
}
}
private void tb_eingabe_GotFocus(object sender, RoutedEventArgs e)
{
tb_eingabe.Text = "";
}
private void btn_submit_Click(object sender, RoutedEventArgs e)
{
submit_message();
}
private void tb_eingabe_KeyDown(object sender, KeyEventArgs e)
{
if (e.Key == Key.Return)
{
submit_message();
}
}
void submit_message()
{
if (tb_eingabe.Text != "")
{
string data = name + " says >> " + tb_eingabe.Text;
SendMessage(data);
tb_eingabe.Clear(); // clear the textbox-values
tb_eingabe.Focus(); // get focus on tb if the submit button was used, the tb lost the focus
}
}
private void SendMessage(string data)
{
try{
UdpClient sendClient = new UdpClient();
Byte[] message = Encoding.UTF8.GetBytes(data); // use UTF8 for international encoding
IPEndPoint endPoint = new IPEndPoint(IPAddress.Broadcast, 1800); // use a broadcast with the given port
sendClient.Send(message, message.Length, endPoint);
sendClient.Close();
}
catch (Exception e)
{
errorHandler(e);
}
}
private void Window_Closing(object sender, System.ComponentModel.CancelEventArgs e)
{
string data = name + " logged out...";
SendMessage(data); // send a logout message to the other chat peers
}
// debugging functions
static void errorHandler(Exception errorMsg)
{
MessageBox.Show(errorMsg.ToString()); // create a error-message-box
fileWriter(errorMsg.ToString(), true); // call the file-writer function to write the error in a file
}
static void fileWriter(string fileText, bool append)
{
System.IO.StreamWriter file = new System.IO.StreamWriter(".\\Errorfile.txt", append); // locate the error next to the chat.exe
file.WriteLine(GetTime(DateTime.Now) + "\n " + fileText); // append the date
file.Close();
}
public static String GetTime(DateTime val)
{
return val.ToString("yyyyMMddHHmmssffff"); // return the current date as string
}
}
}

Instead of IPAddress.Broadcast(255.255.255.255) provide your local network broadcast address. See the example below:
IPAddress broadcast = IPAddress.Parse("192.168.1.255"); //replace the address with your local network.
IPEndPoint endPoint = new IPEndPoint(broadcast, 11000);
sendClient.Send(message, message.Length, endPoint);
IPAddress.Broadcast doesn't work in some network.

Download multiple files in parallel using c#

I want to download files in parallel using C#. For this, I have written this code which is working perfectly but the problem is that UI is freezing.
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Net;
using System.Text;
using System.Text.RegularExpressions;
using System.Threading;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using System.Windows.Threading;
namespace FileDownloader
{
/// <summary>
/// Interaction logic for MainWindow.xaml
/// </summary>
public partial class MainWindow : Window
{
private static int count = 1;
private static string f= "lecture";
private string URL = "www.someexample.com";
public MainWindow()
{
InitializeComponent();
}
public static string GetDirectoryListingRegexForUrl(string url)
{
if (url.Equals(URL))
{
return "(?<name>.*)";
}
throw new NotSupportedException();
}
public void DownloadP(string[] urls)
{
Parallel.ForEach(urls.ToList(), new ParallelOptions { MaxDegreeOfParallelism = 10 }, DownloadFile);
}
private void DownloadFile(string url)
{
using(WebClient client=new WebClient())
{
if (url.EndsWith(".pdf"))
{
int nextIndex = Interlocked.Increment(ref count);
client.DownloadFile(url, f + nextIndex + ".pdf");
this.Dispatcher.Invoke(() => {
listbox.Items.Add(url);
});
}
}
}
private void Button_Click(object sender, RoutedEventArgs e)
{
DownloadP(listofFiles);
}
}
}

You can use async/await with conjunction with new WebClient method DownloadFileTaskAsync.
private async Task DownloadFile(string url)
{
if (!url.EndsWith(".pdf"))
{
return;
}
using (var client = new WebClient())
{
int nextIndex = Interlocked.Increment(ref count);
await client.DownloadFileTaskAsync(url, "lecture" + nextIndex + ".pdf");
listBox.Items.Add(url);
}
}
private async void Button_OnClick(object sender, RoutedEventArgs e)
{
button.IsEnabled = false;
await DownloadFiles(urlList);
button.IsEnabled = true;
}
private async Task DownloadFiles(IEnumerable<string> urlList)
{
foreach (var url in urlList)
{
await DownloadFile(url);
}
}

Relace your DownloadP function with this :
public async Task DownloadP(string[] urls)
{
await Task.Factory.StartNew(() => Parallel.ForEach(urls.ToList(), new ParallelOptions { MaxDegreeOfParallelism = 10 }, DownloadFile));
}

instead of using client.DownloadFile use client.DownloadFileAsync like this
var webClient=new WebClient();
webClient.DownloadFileCompleted += webClient_DownloadFileCompleted;
webClient.DownloadFileAsync("Your url","file_name");
the event
private void webClient_DownloadFileCompleted(object sender, AsyncCompletedEventArgs e)
{
MessageBox.Show("Download Completed.");
}

I know this Question is old, but WebClient is outdated and dedicated.
First of all, WPF uses MVVM pattern that you should try to follow, but except that you can use the HttpClient in using System.Net.Http;.
To download multiple files in a parallel you can create a parallel foreach that handles all the downloads that the HttpClient have to perform. You did tis right but the foreach will block the thread so start it in a new one Task.Run(()=>{// Your Code});
In the case you don’t want do write something like that yourself, you could use the Shard Download Library on NuGet. This NuGet Package is also on GitHub if you want to see how it does its job. It helped me often if I want do download a lot of files, because is does not block the UI thread and is easy to use. To use it you have to write something like this:
void Download()
{
string[] links = new string[]{
"https://google.com",
"https://speed.hetzner.de/100MB.bin",
"https://file-examples.com/storage/fe88dacf086398d1c98749c/2017/04/file_example_MP4_1920_18MG.mp4" };
foreach (var link in links)
{
_ = new LoadRequest(link);
}
Console.ReadLine();
}
But you can also set the MaxDegreeOfParalism and you can change it while it is downloading. You can set the Path for the output file and name it. The problem that the HttpClient has with download finished and progress report is also solved with this. The bad thing is that the documentation of this library is not very good. Here an example with few options as an example.
async Task DownloadAsync()
{
string[] links = new string[]{
"https://google.com",
"https://speed.hetzner.de/100MB.bin",
"https://file-examples.com/storage/fe88dacf086398d1c98749c/2017/04/file_example_MP4_1920_18MG.mp4" };
RequestHandler requestHandler = new()
{
MaxDegreeOfParallelism = 10
};
LoadRequestOptions option = new()
{
Progress = new Progress<float>(value => Console.WriteLine(value.ToString("0.0%"))),
DestinationPath = "C:\\Users\\[UserName]\\Desktop\\",
RequestCompleated = path => Console.WriteLine("Finished: " + path?.ToString()),
RequestHandler = requestHandler
};
LoadRequest last = null;
foreach (string link in links)
{
last = new LoadRequest(link, option);
}
await last.Task;
}
I hope that can help people that have the same problem and don’t want to use the dedicated WebClient.

C# Program stops responding after second WebClient.DownloadString()

I am working on a program for proof of concept that does a webrequest using WebClient.DownloadString("http://website/members/login.php?user=" + textBox1.Text + "&pass=" + textBox2.Text);
to get the boolean value of wether or not the user is a valid login and then if it is it gives a success notification if it isn't ten it gives a fail notification.
The problem is when i press the button to try and login the first time it works fine but when i press it again the second tine the program freezes and gets stuck at the Webclient.download string.
If anyone can spot and tell me whats wrong that would be great. I am providing the code below:
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Text;
using System.Net;
using System.IO;
using System.Diagnostics;
using System.Net;
using System.Collections;
namespace WindowsFormsApplication2
{
public partial class Form1 : Form
{
public static WebClient webclient = new WebClient();
HttpWebResponse wResp;
WebRequest wReq;
bool isConnected = false;
private String Session = "";
public Form1()
{
InitializeComponent();
}
public Boolean checkUser(String username, String password)
{
String login = `webclient.DownloadString("http://connorbp.info/members/auth.php?user=" + textBox1.Text + "&pass=" + textBox2.Text);`
Boolean bLogin = Boolean.Parse(login);
if (bLogin)
{
Session = username + "-" + password;
}
return bLogin;
}
public int CanConnect(string dUrl)
{
wReq = WebRequest.Create(dUrl);
int cnt = Connect();
return cnt;
}
private int Connect()
{
try
{
wResp = (HttpWebResponse)wReq.GetResponse();
isConnected = true;
return 1;
}
catch (Exception)
{
return 0;
}
}
private void button1_Click(object sender, EventArgs e)
{
int init = CanConnect("http://connorbp.info/members/auth.php");
if (init == 0)
{
notifyIcon1.ShowBalloonTip(200, "CBP Login", "Failed to connect to server! Try again later.", ToolTipIcon.Error);
}
else
{
if(checkUser(textBox1.Text, textBox2.Text))
{
notifyIcon1.ShowBalloonTip(20, "CBP Login", "Logged In!", ToolTipIcon.Info);
}
else
{
notifyIcon1.ShowBalloonTip(20, "CBP Login", "Invalid Username/Password!", ToolTipIcon.Error);
}
}
}
private void Form1_Load(object sender, EventArgs e)
{
this.MaximizeBox = false;
notifyIcon1.ShowBalloonTip(20, "CBP Login", "for more cool things go to http://connorbp.info", ToolTipIcon.Info);
}
}
}

You are not closing the response.
The second call is trying to open something that is already open, therefore it hangs.

Is it bad Ju-ju that the port is still being listened to after my app shuts down?

My app listens on a certain port for socket messages. I can see that it is LISTENING via "netstat -a" at the command line.
When I shut the app down, the machine is still listening on that port when I re-run "netstat -a"
Is this a problem?
It seems like maybe it is, as when I subsequently start the app again, it crashes ignominiously.
How can I cause the listening to cease?
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.IO;
using System.Net;
using System.Net.Sockets;
using System.Threading;
using System.Diagnostics;
namespace testSocketSendAndReceive_Nutshell
{
public partial class Form1 : Form
{
string sJerrysIPAddr = "10.24.93.110";
string sMyIPAddr = "10.24.93.128";
string sThisAppFileName = string.Empty;
bool bThisInstanceFunctionsAsServer = false;
internal static Form1 MainSocketPairForm = null;
public Form1()
{
InitializeComponent();
MainSocketPairForm = this;
}
private void Form1_Load(object sender, EventArgs e)
{
sThisAppFileName = System.Diagnostics.Process.GetCurrentProcess().ProcessName; // This provides just the app name, appending ".vshost" but NOT ".exe" (testSocketSendAndReceive_Nutshell.vshost)
lblFileName.Text = sThisAppFileName;
// Client and Server code are here combined in one app; however, we want each instance to run as
// just one or the other, so (the .exe functioning as a Server should be renamed with the subString
// "Server" somewhere in the filename):
bThisInstanceFunctionsAsServer = sThisAppFileName.Contains("Server");
if (bThisInstanceFunctionsAsServer)
{
new Thread(Server).Start(); // Run server method concurrently.
Thread.Sleep(500); // Give server time to start.
}
btnSendMsg.Visible = !bThisInstanceFunctionsAsServer;
textBox1.Visible = !bThisInstanceFunctionsAsServer;
}
static void Client()
{
using (TcpClient client = new TcpClient(Form1.MainSocketPairForm.sJerrysIPAddr, 51111)) // err here second time around
using (NetworkStream n = client.GetStream())
{
BinaryWriter w = new BinaryWriter(n);
w.Write(Form1.MainSocketPairForm.textBox1.Text.ToString());
w.Flush();
Form1.MainSocketPairForm.label1.Text = new BinaryReader(n).ReadString();
}
}
static void Server()
{
TcpListener listener = new TcpListener(IPAddress.Any, 51111);
listener.Start();
var shouldExit = false;
while (!shouldExit)
using (TcpClient c = listener.AcceptTcpClient())
{
using (NetworkStream n = c.GetStream())
{
string msg = new BinaryReader(n).ReadString();
if (msg == "exit")
// Client told us to exit...
shouldExit = true;
BinaryWriter w = new BinaryWriter(n);
w.Write(msg + " back atcha!");
w.Flush(); // Must call Flush because we're not disposing the writer.
}
}
}
private void button1_Click(object sender, EventArgs e)
{
Client();
}
private void button2_Click(object sender, EventArgs e)
{
Close();
}
}
}

Your application is probably not actually exiting (check task manager "Processes" tab for your .exe).
You are probably trying to close the application by just closing the command window. Because your Server thread is not a background thread, it will just keep running. Try this guy in Form_Load:
if (bThisInstanceFunctionsAsServer)
{
var serverThread = new Thread(Server);
serverThread.IsBackground = true; // Make sure the server thread doesn't keep the app running in the background
serverThread.Start(); // Run server method concurrently.
Thread.Sleep(500); // Give server time to start.
}