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Xamarin forms - can't scan BLE devices

I new in Xamarin forms and C#.
I am trying to scan BLE device using the native Xamarin forms API, the code attached. I am using the Xiomi note 5 running android 9.
using Android.Bluetooth;
using Android.Bluetooth.LE;
using Android.Runtime;
using System;
using System.Collections.Generic;
using System.ComponentModel;
using Xamarin.Forms;
namespace bletest
{
// Learn more about making custom code visible in the Xamarin.Forms previewer
// by visiting https://aka.ms/xamarinforms-previewer
[DesignTimeVisible(false)]
public class MyScanCallback : ScanCallback
{
public override void OnBatchScanResults(IList<ScanResult> results)
{
base.OnBatchScanResults(results);
}
public override void OnScanResult([GeneratedEnum] ScanCallbackType callbackType, ScanResult result)
{
base.OnScanResult(callbackType, result);
}
public override void OnScanFailed([GeneratedEnumAttribute] ScanFailure errorCode)
{
base.OnScanFailed(errorCode);
}
}
public class newbtle
{
private readonly BluetoothAdapter _ba;
private readonly BluetoothLeScanner _sc;
private readonly MyScanCallback _scCb;
public newbtle()
{
_ba = BluetoothAdapter.DefaultAdapter;
_sc = _ba.BluetoothLeScanner;
_scCb = new MyScanCallback();
}
public void BleScan()
{
if (_ba.Enable() == true)
{
_sc.StartScan(_scCb);
}
}
public void BleScanStop()
{
_sc.StopScan(_scCb);
_sc.FlushPendingScanResults(_scCb);
_ba.Disable();
}
public string GetScanMode()
{
return _ba.ScanMode.ToString();
}
public string GetStateMode()
{
return _ba.State.ToString();
}
}
public partial class MainPage : ContentPage
{
newbtle bt = new newbtle();
public MainPage()
{
InitializeComponent();
}
private void Button_Clicked(object sender, EventArgs e)
{
bt.BleScan();
}
private void Button_Clicked_1(object sender, EventArgs e)
{
bt.BleScanStop();
}
}
}
When a call is made to bt.BleScan no call back is called, when the bt.BleScan called in the second time without turning the scanner off the OnScanFailed is called with 'already active error'.
When I run the BLE explorer utility on the same mobile in the same environment it scan few BLE devices.
Any suggestion what can be the problem?
Thanks

foreground service never stop xamarin android

i have xamarin android application that read from clipboard and write to it. it uses foreground services if the user hit the button. the problem is when the user hit the button again the services disappear from running services but still doing it's job (editing copied text). how can i completely stop it from working?
foreground.cs:
public override IBinder OnBind(Intent intent)
{
return null;
}
public override StartCommandResult OnStartCommand(Intent intent, StartCommandFlags flags, int startId)
{
Clipboard.ClipboardContentChanged += async (o, e) =>
{
var text = await Clipboard.GetTextAsync();
Toast.MakeText(this, text, ToastLength.Long).Show();
if (text.Contains("#"))
{
await Clipboard.SetTextAsync(text.Replace("#", ""));
}
};
Notification notif = ReturnNotif();
StartForeground(1, notif);
return StartCommandResult.NotSticky;
}
public override void OnDestroy()
{
base.OnDestroy();
}
public override void OnCreate()
{
base.OnCreate();
}
public override bool StopService(Intent name)
{
StopForeground(true);
StopSelf();
return base.StopService(name);
}
MainActivity.cs:
if (id == Resource.Id.myService)
{
if (count != 1)
{
count = 1;
var intent = new Intent(this, typeof(foreground));
intent.SetAction("No");
if (Build.VERSION.SdkInt >= BuildVersionCodes.O)
{
StartForegroundService(intent);
}
else
{
StartService(intent);
}
}
else
{
var intent = new Intent(this,typeof(foreground));
StopService(intent);
Toast.MakeText(this, "Service Stopped", ToastLength.Long).Show();
count = 0;
}
}
what i am doing wrong ?
Edit :
Service will completely stops if the app is removed from recently used apps.

In your MyForegroundService.cs. Just add StopForeground(true) in OnDestroy() method like following code.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Android.App;
using Android.Content;
using Android.OS;
using Android.Runtime;
using Android.Views;
using Android.Widget;
namespace ForegroundServiceDemo
{
[Service]
class MyForegroundService : Service
{
public const int SERVICE_RUNNING_NOTIFICATION_ID = 10000;
[return: GeneratedEnum]
public override StartCommandResult OnStartCommand(Intent intent, [GeneratedEnum] StartCommandFlags flags, int startId)
{
CreateNotificationChannel();
string messageBody = "service starting";
// / Create an Intent for the activity you want to start
Intent resultIntent = new Intent(this,typeof(Activity1));
// Create the TaskStackBuilder and add the intent, which inflates the back stack
TaskStackBuilder stackBuilder = TaskStackBuilder.Create(this);
stackBuilder.AddNextIntentWithParentStack(resultIntent);
// Get the PendingIntent containing the entire back stack
PendingIntent resultPendingIntent = stackBuilder.GetPendingIntent(0, PendingIntentFlags.UpdateCurrent);
var notification = new Notification.Builder(this, "10111")
.SetContentIntent(resultPendingIntent)
.SetContentTitle("Foreground")
.SetContentText(messageBody)
.SetSmallIcon(Resource.Drawable.main)
.SetOngoing(true)
.Build();
StartForeground(SERVICE_RUNNING_NOTIFICATION_ID, notification);
//do you work
return StartCommandResult.Sticky;
}
public override void OnDestroy()
{
base.OnDestroy();
StopForeground(true);
}
public override IBinder OnBind(Intent intent)
{
return null;
}
void CreateNotificationChannel()
{
if (Build.VERSION.SdkInt < BuildVersionCodes.O)
{
return;
}
var channelName = Resources.GetString(Resource.String.channel_name);
var channelDescription = GetString(Resource.String.channel_description);
var channel = new NotificationChannel("10111", channelName, NotificationImportance.Default)
{
Description = channelDescription
};
var notificationManager = (NotificationManager)GetSystemService(NotificationService);
notificationManager.CreateNotificationChannel(channel);
}
}
}
When you want to stop it. Just call following code.
Android.App.Application.Context.StopService(intent);
Here is my code in the Activity.
public class MainActivity : AppCompatActivity
{
protected override void OnCreate(Bundle savedInstanceState)
{
base.OnCreate(savedInstanceState);
Xamarin.Essentials.Platform.Init(this, savedInstanceState);
// Set our view from the "main" layout resource
SetContentView(Resource.Layout.activity_main);
Button button1 = FindViewById<Button>(Resource.Id.button1);
Button button2 = FindViewById<Button>(Resource.Id.button2);
button2.Click += Button2_Click;
button1.Click += Button1_Click;
}
Intent intent;
private void Button2_Click(object sender, System.EventArgs e)
{
// stop foreground service.
Android.App.Application.Context.StopService(intent);
}
private void Button1_Click(object sender, System.EventArgs e)
{
intent = new Intent(Android.App.Application.Context, typeof(MyForegroundService));
// start foreground service.
if (Android.OS.Build.VERSION.SdkInt >= Android.OS.BuildVersionCodes.O)
{
StartForegroundService(intent);
}
}
Here is running GIF.
====Update====
the expected behavior is : when service stopped user can copy and paste normally without the service interference
You can use following way to achieve that.Use Clipboard.ClipboardContentChanged += Clipboard_ClipboardContentChanged; to execute the behavior, use Clipboard.ClipboardContentChanged -= Clipboard_ClipboardContentChanged; to disable the behavior in the OnDistory method.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Android.App;
using Android.Content;
using Android.OS;
using Android.Runtime;
using Android.Views;
using Android.Widget;
using Xamarin.Essentials;
namespace ForegroundServiceDemo
{
[Service]
class MyForegroundService : Service
{
public const int SERVICE_RUNNING_NOTIFICATION_ID = 10000;
[return: GeneratedEnum]
public override StartCommandResult OnStartCommand(Intent intent, [GeneratedEnum] StartCommandFlags flags, int startId)
{
CreateNotificationChannel();
string messageBody = "service starting";
Clipboard.ClipboardContentChanged += Clipboard_ClipboardContentChanged;
// / Create an Intent for the activity you want to start
Intent resultIntent = new Intent(this,typeof(Activity1));
// Create the TaskStackBuilder and add the intent, which inflates the back stack
TaskStackBuilder stackBuilder = TaskStackBuilder.Create(this);
stackBuilder.AddNextIntentWithParentStack(resultIntent);
// Get the PendingIntent containing the entire back stack
PendingIntent resultPendingIntent = stackBuilder.GetPendingIntent(0, PendingIntentFlags.UpdateCurrent);
var notification = new Notification.Builder(this, "10111")
.SetContentIntent(resultPendingIntent)
.SetContentTitle("Foreground")
.SetContentText(messageBody)
.SetSmallIcon(Resource.Drawable.main)
.SetOngoing(true)
.Build();
StartForeground(SERVICE_RUNNING_NOTIFICATION_ID, notification);
//do you work
return StartCommandResult.Sticky;
}
private async void Clipboard_ClipboardContentChanged(object sender, EventArgs e)
{
//throw new NotImplementedException();
var text = await Clipboard.GetTextAsync();
Toast.MakeText(this, text, ToastLength.Long).Show();
if (text.Contains("#"))
{
await Clipboard.SetTextAsync(text.Replace("#", ""));
}
}
public override void OnDestroy()
{
base.OnDestroy();
Clipboard.ClipboardContentChanged -= Clipboard_ClipboardContentChanged;
StopForeground(true);
}
public override IBinder OnBind(Intent intent)
{
return null;
}
void CreateNotificationChannel()
{
if (Build.VERSION.SdkInt < BuildVersionCodes.O)
{
return;
}
var channelName = Resources.GetString(Resource.String.channel_name);
var channelDescription = GetString(Resource.String.channel_description);
var channel = new NotificationChannel("10111", channelName, NotificationImportance.Default)
{
Description = channelDescription
};
var notificationManager = (NotificationManager)GetSystemService(NotificationService);
notificationManager.CreateNotificationChannel(channel);
}
}
}
Here is run GIF.

To prevent this issues, add a "myServiceIsRunning" bool value in the Properties dictionary when you start your foreground method like this:
Application.Current.Properties["myServiceIsRunning"] = true
With a get function or whatever you want, before start the foreground method, verify if the key "myServiceIsRunning" exist, and if it exist, how is his status:
public bool getRunningStateMyService(){
bool myServiceIsRunningValue;
if (Application.Current.Properties.ContainsKey("myServiceIsRunning"))
{
myServiceIsRunningValue = Convert.ToBoolean(Application.Current.Properties["myServiceIsRunning"]);
}
else
{
myServiceIsRunningValue = false;
}
return locationServiceIsRunning;
}
After you get the value, with a simple if{}/else{}, you can choose to start a new instance or not if you're service is running or not. Or, in you're case just prevent the foreground method continue to run.
Don't forget to set your value to false when you destroy the foreground method.
the Properties dictionary can store data trought closing app to. you can have more infos here:
https://learn.microsoft.com/fr-fr/xamarin/xamarin-forms/app-fundamentals/application-class#Properties_Dictionary

UWP Bluetooth Low Energy Application Disconnects Early

So I am designing an application for windows laptops to connect to a custom designed pressure sensor. The application pairs to the device and then receives notifications from the device every 10 ms. Then for some reason the communication stops. I know it is a problem with my application and not with the device, because when I connect to my phone, I do not have this problem.
Here is the main page where I create the devicewatcher and discover the device:
using System;
using System.Collections.ObjectModel;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
using System.Linq;
using System.Runtime.InteropServices.WindowsRuntime;
using Windows.Foundation;
using Windows.Foundation.Collections;
using Windows.UI.Core;
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 Windows.Devices.Bluetooth;
using Windows.Devices.Enumeration;
// The Blank Page item template is documented at https://go.microsoft.com/fwlink/?LinkId=402352&clcid=0x409
namespace BLEInterfaceTest
{
/// <summary>
/// An empty page that can be used on its own or navigated to within a Frame.
/// </summary>
public sealed partial class MainPage : Page
{
private DeviceWatcher deviceWatcher;
private ObservableCollection<DeviceInformation> deviceList = new ObservableCollection<DeviceInformation>();
public MainPage()
{
this.InitializeComponent();
}
protected override void OnNavigatedTo(NavigationEventArgs e)
{
this.DataContext = deviceList;
deviceListView.ItemsSource = deviceList;
deviceWatcher = DeviceInformation.CreateWatcher(
"System.ItemNameDisplay:~~\"Button\"",
new string[] {
"System.Devices.Aep.DeviceAddress",
"System.Devices.Aep.IsConnected" },
DeviceInformationKind.AssociationEndpoint);
deviceWatcher.Added += DeviceWatcher_Added;
deviceWatcher.Removed += DeviceWatcher_Removed;
deviceWatcher.Start();
base.OnNavigatedTo(e);
SystemNavigationManager.GetForCurrentView().AppViewBackButtonVisibility =
AppViewBackButtonVisibility.Collapsed;
}
protected override void OnNavigatedFrom(NavigationEventArgs e)
{
deviceWatcher.Stop();
base.OnNavigatedFrom(e);
}
private async void DeviceWatcher_Removed(DeviceWatcher sender, DeviceInformationUpdate args)
{
var toRemove = (from a in deviceList where a.Id == args.Id select a).FirstOrDefault();
if (toRemove != null)
{
await this.Dispatcher.RunAsync(
Windows.UI.Core.CoreDispatcherPriority.Normal,
() => { deviceList.Remove(toRemove); });
}
}
private async void DeviceWatcher_Added(DeviceWatcher sender, DeviceInformation args)
{
await this.Dispatcher.RunAsync(
Windows.UI.Core.CoreDispatcherPriority.Normal,
() => { deviceList.Add(args); });
}
private void deviceListView_ItemClick(object sender, ItemClickEventArgs e)
{
this.Frame.Navigate(typeof(DevicePage), e.ClickedItem);
}
}
}'
This next code is the page where the pressure sensor is connected to and where data is read from the device.
using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.IO;
using System.Linq;
using System.Runtime.InteropServices.WindowsRuntime;
using Windows.Foundation;
using Windows.Foundation.Collections;
using Windows.UI.Core;
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 Windows.UI.Popups;
using Windows.Devices.Bluetooth.GenericAttributeProfile;
using Windows.Devices.Bluetooth;
using Windows.Devices.Enumeration;
using Windows.Storage.Pickers;
using Windows.Storage;
using Windows.Storage.Streams;
using System.Threading.Tasks;
using Windows.ApplicationModel.Background;
// The Blank Page item template is documented at https://go.microsoft.com/fwlink/?LinkId=234238
namespace BLEInterfaceTest
{
/// <summary>
/// An empty page that can be used on its own or navigated to within a Frame.
/// </summary>
public sealed partial class DevicePage : Page
{
private DeviceInformation device { get; set; }
private PressureSensor pSensor { get; set; }
public static DateTime startTime { get; set; }
public ObservableCollection<DataPoint> PressureData = new ObservableCollection<DataPoint>();
public static ObservableCollection<DataPoint> inbetween;
private static TextBox txtP;
private BluetoothLEDevice leDevice;
private DispatcherTimer timer = new DispatcherTimer();
private int packetNum = 0;
public DevicePage()
{
this.InitializeComponent();
SystemNavigationManager.GetForCurrentView().BackRequested += DevicePage_BackRequested;
txtP = txtValue1;
inbetween = PressureData;
}
public static void ChangeText(string text)
{
txtP.Text = text;
}
private async void InitializePressureSensor(GattDeviceService service)
{
pSensor = new PressureSensor(service, SensorUUIDs.PressureSensorUuid);
await pSensor.EnableNotifications();
btnStart.IsEnabled = true;
}
private async void StartRecievingData()
{
try
{
leDevice = await BluetoothLEDevice.FromIdAsync(device.Id);
string selector = "(System.DeviceInterface.Bluetooth.DeviceAddress:=\"" +
leDevice.BluetoothAddress.ToString("X") + "\")";
var services = await leDevice.GetGattServicesAsync(BluetoothCacheMode.Uncached);
foreach (var service in services.Services)
{
if (service.Uuid.ToString() == SensorUUIDs.ButtonSensorServiceUuid)
{
InitializePressureSensor(service);
}
}
timer.Interval = new TimeSpan(0, 0, 0, 0, 1);
timer.Tick += Timer_Tick1;
startTime = DateTime.Now;
timer.Start();
}
catch (Exception ex)
{
var messageDialog = new MessageDialog("An error has occured Please try again. \n" + ex.Message, "Error!");
}
}
public async void UpdateAllData()
{
while (pSensor != null && pSensor.MorePacketsAvailable)
{
int[] values = await pSensor.GetPressure();
int packetNumber = values[0];
if (packetNumber > packetNum)
{
packetNum = packetNumber;
txtValue1.Text = Convert.ToString(values[1]);
txtValue2.Text = Convert.ToString(values[5]);
for (int i = 1; i < 5; i++)
{
PressureData.Add(new DataPoint(DateTime.Now - startTime, packetNumber, ((i-1)*2.5 + 10*packetNumber), values[i], values[i + 4]));
}
}
}
}
private void Timer_Tick1(object sender, object e)
{
UpdateAllData();
}
private async void PairToDevice()
{
if (device.Pairing.CanPair)
{
var customPairing = device.Pairing.Custom;
customPairing.PairingRequested += CustomPairing_PairingRequested;
var result = await customPairing.PairAsync(DevicePairingKinds.ConfirmOnly);
customPairing.PairingRequested -= CustomPairing_PairingRequested;
if ((result.Status == DevicePairingResultStatus.Paired) || (result.Status == DevicePairingResultStatus.AlreadyPaired))
{
/*while (device.Pairing.IsPaired == false)
{
device = await DeviceInformation.CreateFromIdAsync(device.Id);
}*/
StartRecievingData();
}
}
else if (device.Pairing.IsPaired)
{
StartRecievingData();
}
}
private void CustomPairing_PairingRequested(DeviceInformationCustomPairing sender, DevicePairingRequestedEventArgs args)
{
args.Accept();
}
protected override void OnNavigatedTo(NavigationEventArgs e)
{
btnSave.Content = "Save";
btnStop.IsEnabled = false;
btnStart.IsEnabled = false;
this.DataContext = PressureData;
device = (DeviceInformation)e.Parameter;
PairToDevice();
//StartRecievingData();
base.OnNavigatedTo(e);
Frame rootFrame = Window.Current.Content as Frame;
if (rootFrame.CanGoBack)
{
SystemNavigationManager.GetForCurrentView().AppViewBackButtonVisibility =
AppViewBackButtonVisibility.Visible;
}
}
private void DevicePage_BackRequested(object sender, BackRequestedEventArgs eventArgs)
{
Frame rootFrame = Window.Current.Content as Frame;
if (rootFrame == null)
{
return;
}
// Navigate back if possible, and if the event has already been handled
if (rootFrame.CanGoBack && eventArgs.Handled ==false)
{
eventArgs.Handled = true;
rootFrame.GoBack();
}
}
private async void btnSave_Click(object sender, RoutedEventArgs e)
{
timer.Stop();
var picker = new FileSavePicker();
picker.SuggestedStartLocation = PickerLocationId.DocumentsLibrary;
picker.FileTypeChoices.Add("CSV", new List<string>() { ".csv" });
StorageFile file = await picker.PickSaveFileAsync();
if (file != null)
{
var stream = await file.OpenAsync(FileAccessMode.ReadWrite);
using (IOutputStream outputStream = stream.GetOutputStreamAt(0))
{
using (var writer = new DataWriter(outputStream))
{
foreach (DataPoint p in PressureData)
{
string text = p.TimeStamp.ToString() + "," + p.PacketNumber.ToString() + "," + p.InternalTimestamp.ToString() + "," + p.PressureValue1.ToString() + "," + p.PressureValue2.ToString() + "\n";
writer.WriteString(text);
}
await writer.StoreAsync();
await writer.FlushAsync();
}
}
stream.Dispose();
}
}
private async void btnStart_Click(object sender, RoutedEventArgs e)
{
if (pSensor != null)
{
btnStop.IsEnabled = true;
btnStart.IsEnabled = false;
startTime = DateTime.Now;
if (pSensor != null)
{
await pSensor.BeginCollecting();
}
}
}
private async void btnStop_Click(object sender, RoutedEventArgs e)
{
btnStart.IsEnabled = true;
btnStop.IsEnabled = false;
if (pSensor != null)
{
await pSensor.StopCollecting();
}
}
}
}
Here is where I define my SensorBase and PressureSensor class that handles the device connection:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Windows.Devices.Bluetooth;
using Windows.Devices.Bluetooth.GenericAttributeProfile;
using Windows.Storage.Streams;
using Windows.Devices.Enumeration;
namespace BLEInterfaceTest
{
public static class SensorUUIDs
{
private static readonly string _packetUuid = "0000a043-0000-1000-8000-00805f9b34fb";
private static readonly string _buttonSensorServiceUuid = "0000a042-0000-1000-8000-00805f9b34fb";
private static readonly string _sensorStateUuid = "0000a044-0000-1000-8000-00805f9b34fb";
public static string PressureSensorUuid
{
get { return _packetUuid; }
}
public static string ButtonSensorServiceUuid
{
get { return _buttonSensorServiceUuid; }
}
public static string SensorStateUuid
{
get { return _sensorStateUuid; }
}
}
public class SensorBase : IDisposable
{
protected GattDeviceService deviceService;
protected string sensorDataUuid;
protected Queue<byte[]> fifoBuffer;
protected bool isNotificationSupported = false;
public bool newData = false;
private GattCharacteristic dataCharacteristic;
public SensorBase(GattDeviceService dataService, string sensorDataUuid)
{
this.deviceService = dataService;
this.sensorDataUuid = sensorDataUuid;
fifoBuffer = new Queue<byte[]>(20);
}
public bool MorePacketsAvailable
{
get
{
if (fifoBuffer.Count > 0)
{
return true;
}
else
{
return false;
}
}
}
public virtual async Task EnableNotifications()
{
GattCharacteristicsResult result = await deviceService.GetCharacteristicsAsync();
foreach (var test in result.Characteristics)
{
string t = test.Uuid.ToString();
}
isNotificationSupported = true;
dataCharacteristic = (await deviceService.GetCharacteristicsForUuidAsync(
new Guid(sensorDataUuid))).Characteristics[0];
dataCharacteristic.ValueChanged += dataCharacteristic_ValueChanged;
GattCommunicationStatus status = await dataCharacteristic.WriteClientCharacteristicConfigurationDescriptorAsync(
GattClientCharacteristicConfigurationDescriptorValue.Notify);
var currentDescriptorValue = await dataCharacteristic.ReadClientCharacteristicConfigurationDescriptorAsync();
if (currentDescriptorValue.Status != GattCommunicationStatus.Success
|| currentDescriptorValue.ClientCharacteristicConfigurationDescriptor != GattClientCharacteristicConfigurationDescriptorValue.Notify)
{
GattCommunicationStatus status2 = await dataCharacteristic.WriteClientCharacteristicConfigurationDescriptorAsync(
GattClientCharacteristicConfigurationDescriptorValue.Notify);
}
}
public virtual async Task DisableNotifications()
{
newData = false;
isNotificationSupported = false;
dataCharacteristic = (await deviceService.GetCharacteristicsForUuidAsync(
new Guid(sensorDataUuid))).Characteristics[0];
dataCharacteristic.ValueChanged -= dataCharacteristic_ValueChanged;
GattCommunicationStatus status = await dataCharacteristic.WriteClientCharacteristicConfigurationDescriptorAsync(GattClientCharacteristicConfigurationDescriptorValue.None);
}
protected async Task<byte[]> ReadValue()
{
if (!isNotificationSupported)
{
if (dataCharacteristic == null)
{
dataCharacteristic = (await deviceService.GetCharacteristicsForUuidAsync(
new Guid(sensorDataUuid))).Characteristics[0];
}
GattReadResult readResult = await dataCharacteristic.ReadValueAsync();
byte[] data = new byte[readResult.Value.Length];
DataReader.FromBuffer(readResult.Value).ReadBytes(data);
fifoBuffer.Enqueue(data);
}
return fifoBuffer.Dequeue();
}
protected async Task WriteByteArray(string characteristicUuid, byte[] value)
{
GattCharacteristic writeCharacteristic = (await deviceService.GetCharacteristicsForUuidAsync(
new Guid(characteristicUuid))).Characteristics[0];
var writer = new DataWriter();
writer.WriteBytes(value);
var res = await writeCharacteristic.WriteValueAsync(writer.DetachBuffer(), GattWriteOption.WriteWithoutResponse);
}
private void dataCharacteristic_ValueChanged(GattCharacteristic sender, GattValueChangedEventArgs args)
{
byte[] data = new byte[args.CharacteristicValue.Length];
DataReader.FromBuffer(args.CharacteristicValue).ReadBytes(data);
fifoBuffer.Enqueue(data);
newData = true;
}
public async void Dispose()
{
await DisableNotifications();
}
}
public class PressureSensor: SensorBase
{
public PressureSensor(GattDeviceService dataService, string sensorDataUuid)
: base(dataService, sensorDataUuid)
{
}
public async Task BeginCollecting()
{
await WriteByteArray(SensorUUIDs.SensorStateUuid, new byte[] { 0x01 });
}
public async Task<int[]> GetPressure()
{
byte[] data = await ReadValue();
if (data != null)
{
int[] values = new int[9];
values[0] = (int)BitConverter.ToInt32(data, 0);
for (int i = 1; i < values.Length; i++)
{
values[i] = (int)BitConverter.ToInt16(data, 2 * i + 2);
}
return values;
}
else
{
return new int[] { 0 };
}
}
public async Task StopCollecting()
{
await WriteByteArray(SensorUUIDs.SensorStateUuid, new byte[] { 0x00 });
}
}
}
Here is the DataPoint Class that I use to organize the data received from the pressure sensor:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.ComponentModel;
using System.Runtime.CompilerServices;
namespace BLEInterfaceTest
{
public class DataPoint : INotifyPropertyChanged
{
private TimeSpan _timestamp;
private int _packetNumber;
private double _internalTimestamp;
private int _pressure1;
private int _pressure2;
public event PropertyChangedEventHandler PropertyChanged;
public TimeSpan TimeStamp
{
get { return _timestamp; }
set
{
_timestamp = value;
this.NotifyPropertyChanged();
}
}
public int PacketNumber
{
get { return _packetNumber; }
set
{
_packetNumber = value;
this.NotifyPropertyChanged();
}
}
public double InternalTimestamp
{
get { return _internalTimestamp; }
set
{
_internalTimestamp = value;
this.NotifyPropertyChanged();
}
}
public int PressureValue1
{
get { return _pressure1; }
set
{
_pressure1 = value;
this.NotifyPropertyChanged();
}
}
public int PressureValue2
{
get { return _pressure2; }
set
{
_pressure2 = value;
this.NotifyPropertyChanged();
}
}
public DataPoint(TimeSpan time,int packetNumber, double internalTimestamp, int pressure1, int pressure2)
{
_timestamp = time;
_packetNumber = packetNumber;
_internalTimestamp = internalTimestamp;
_pressure1 = pressure1;
_pressure2 = pressure2;
}
private void NotifyPropertyChanged([CallerMemberName] string propertyName = "")
{
if (!string.IsNullOrEmpty(propertyName))
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
}
}
I have researched this extensively, and all I could find was help on how to initiate a disconnection. I have the opposite problem. One page I found stated that the problem might be caused by the device not properly storing the bonding state, but I have checked that and I did initialize the device to save the bonding state.
Interestingly if I do not pair the device to the computer before trying to read information from it then I do not have the problem. The connection never randomly stops. But when I do this, the computer does not receive every packet of data sent from the sensor device. It will receive one or two packets and then skip five or six packets. If I pair the device then I will receive every packet but the connection will randomly cut off.
So my question is two fold, I guess. How do I stop the connection from cutting off when the device is paired? Or alternatively, is there a way to allow the application to receive every packet of data when it is not paired?
UPDATE
I realized I should include more information on my sensor peripheral in case the error is in that code. I am currently designing a rapid prototyping of this sensor before I move on to designing the embedded version. To do this, I am using the BLE Nano 1 from RedBearLabs as a user friendly prototype. I am programing this device with the online MBED compiler. I have included the nRF51822 and BLE_API libraries to handle the bluetooth low energy communication.
UPDATE 2
So after more research into what is causing the problem, I have found that the disconnection occurs when a connection interval and a generation 2 garbage collection occur at the same time. In UWP the garbage collector can pause the UI Thread for generation 2 collections. (see here)
My thought is that if the thread is paused at the beginning of a connection interval, then the central is not able to initiate the connection with the peripheral and the peripheral therefore thinks the client is no longer listening (see more about how BLE connections work).
I discovered this by finding out exactly what is necessary to get the connection back once it has randomly stopped. I started with the entire connection process and reduced it down to this:
public async Task ReconnectDevice()
{
GattCommunicationStatus status = await dataCharacteristic.WriteClientCharacteristicConfigurationDescriptorAsync(
GattClientCharacteristicConfigurationDescriptorValue.Notify);
await WriteByteArray(SensorUUIDs.SensorStateUuid, new byte[] { 0x01 });
}
Because my BluetoothLEDevice, GattService, and GattCharacteristic objects are not disposed, all I need to do is resubscribe to notifications and write a 1 to the device so that it begins collecting data again.
I have reduced my memory allocations in my application significantly since discovering this, and the time for a gen2 collection has decreased to an average of 5 ms. Also, the amount of time before the connection disconnects has increased to around 4-5 sec.
UWP has a GattCharacteristicNotificationTrigger for receiving notifications in a BackgroundTask, but I have never had much success at incorporating background tasks in UWP.
I think I will try next to incorporate the windows.devices into a WPF application where I think I will have a better chance at getting it working.

So, after a while of trying different ideas I have finally stumbled across a solution to my problem. I had to make 2 changes:
Used the unpaired connection instead of the paired connection. This solved the problem of the connection dropping suddenly.
Increased the connection interval to 40 ms. For some reason when I did this, I received all of the data and no longer had any problems. Anything below 40 ms causes information to be lost when communicating to a Windows device (I had to make this change on the C code running on my sensors.)
I have used the devices for about 2 months now after making this change and have had no problems at all.

I seems to me that these problems are related to the BluetoothCacheMode Enum.
This indicates whether certain Bluetooth API methods should operate on values cached in the system or
retrieve those values from the Bluetooth device.
Using BluetoothCacheMode.Uncached attribute allows the service to update the attributes when needed.
If the device is paired then the BluetoothCacheMode is not needed(I think BluetoothCacheMode.Cached is default).
In your code the line:
var services = await leDevice.GetGattServicesAsync(BluetoothCacheMode.Uncached);
Can be the cause of the connection lost if paired.
GetGattServicesAsync(), GetCharacteristicsAsync() and ReadValueAsync()
must have the attribute BluetoothCacheMode.Uncached when not paired, when paired default or BluetoothCacheMode.Cached.
See https://msdn.microsoft.com/en-us/library/windows/apps/dn263758.aspx.

Using Accord Audio library with Windows Phone 8.1 App (Not Silverlight)

I'm currently building an application for Windows Phone 8.1 using C#,
The aim of the app is to assess audio signals from the device's microphone, initially for frequency,
I was hoping to use the Accord library to help with this but have run into these errors:
XamlCompiler error WMC1006: Cannot resolve Assembly or Windows
Metadata file 'System.Windows.Forms.dll'
\Program Files
(x86)\MSBuild\Microsoft\WindowsXaml\v12.0\8.1\Microsoft.Windows.UI.Xaml.Common.targets(327,9):
Xaml Internal Error error WMC9999: Type universe cannot resolve
assembly: System.Windows.Forms, Version=4.0.0.0, Culture=neutral,
PublicKeyToken=b77a5c561934e089.
I'm fairly certain that this is arising due to the references included in the project but I'm not to sure,
Here is my current code:
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 Accord.Audio;
using Accord.Controls;
using Accord.DirectSound;
using Accord.Imaging;
using Accord.MachineLearning;
using Accord.Math;
using Accord.Statistics;
using Accord;
using AForge;
using AForge.Controls;
using AForge.Imaging;
using AForge.Math;
using AForge.Video;
using Windows.Media.Capture;
using Windows.Storage;
using Windows.Storage.Streams;
using Windows.Storage.Pickers;
using System.Diagnostics;
using Windows.Media;
using Windows.Media.MediaProperties;
using Accord.Audio.Formats;
using Accord.Audio.Windows;
namespace Test2
{
public sealed partial class MainPage : Page
{
private MediaCapture _mediaCaptureManager;
private StorageFile _recordStorageFile;
private bool _recording;
private bool _userRequestedRaw;
private bool _rawAudioSupported;
private IRandomAccessStream _audioStream;
private FileSavePicker _fileSavePicker;
private DispatcherTimer _timer;
private TimeSpan _elapsedTime;
public MainPage()
{
this.InitializeComponent();
this.NavigationCacheMode = NavigationCacheMode.Required;
InitializeAudioRecording();
}
private static void DecodeAudioFile()
{
String fileName = "record.wav";
WaveDecoder sourceDecoder = new WaveDecoder(fileName);
Signal sourceSignal = sourceDecoder.Decode();
RaisedCosineWindow window = RaisedCosineWindow.Hamming(1024);
Signal[] windows = sourceSignal.Split(window, 512);
ComplexSignal[] complex = windows.Apply(ComplexSignal.FromSignal);
complex.ForwardFourierTransform();
Debug.WriteLine(complex);
}
protected override void OnNavigatedTo(NavigationEventArgs e)
{
}
private async void InitializeAudioRecording()
{
_mediaCaptureManager = new MediaCapture();
var settings = new MediaCaptureInitializationSettings();
settings.StreamingCaptureMode = StreamingCaptureMode.Audio;
settings.MediaCategory = MediaCategory.Other;
settings.AudioProcessing = (_rawAudioSupported && _userRequestedRaw) ? AudioProcessing.Raw : AudioProcessing.Default;
await _mediaCaptureManager.InitializeAsync(settings);
Debug.WriteLine("Device initialised successfully");
_mediaCaptureManager.RecordLimitationExceeded += new RecordLimitationExceededEventHandler(RecordLimitationExceeded);
_mediaCaptureManager.Failed += new MediaCaptureFailedEventHandler(Failed);
}
private void Failed(MediaCapture sender, MediaCaptureFailedEventArgs errorEventArgs)
{
throw new NotImplementedException();
}
private void RecordLimitationExceeded(MediaCapture sender)
{
throw new NotImplementedException();
}
private async void CaptureAudio()
{
try
{
Debug.WriteLine("Starting record");
String fileName = "record.wav";
_recordStorageFile = await KnownFolders.VideosLibrary.CreateFileAsync(fileName, CreationCollisionOption.GenerateUniqueName);
Debug.WriteLine("Create record file successfully");
Debug.WriteLine(fileName);
MediaEncodingProfile recordProfile = MediaEncodingProfile.CreateWav(AudioEncodingQuality.Auto);
await _mediaCaptureManager.StartRecordToStorageFileAsync(recordProfile, this._recordStorageFile);
Debug.WriteLine("Start Record successful");
_recording = true;
}
catch (Exception e)
{
Debug.WriteLine("Failed to capture audio");
}
DecodeAudioFile();
}
private async void StopCapture()
{
if (_recording)
{
Debug.WriteLine("Stopping recording");
await _mediaCaptureManager.StopRecordAsync();
Debug.WriteLine("Stop recording successful");
_recording = false;
}
}
private async void PlayRecordedCapture()
{
if (!_recording)
{
var stream = await _recordStorageFile.OpenAsync(FileAccessMode.Read);
Debug.WriteLine("Recording file opened");
playbackElement1.AutoPlay = true;
playbackElement1.SetSource(stream, _recordStorageFile.FileType);
playbackElement1.Play();
}
}
private void Capture_Click(object sender, RoutedEventArgs e)
{
Capture.IsEnabled = false;
Stop.IsEnabled = true;
CaptureAudio();
}
private void Stop_Click(object sender, RoutedEventArgs e)
{
Capture.IsEnabled = true;
Stop.IsEnabled = false;
StopCapture();
}
private void Playback_Click(object sender, RoutedEventArgs e)
{
PlayRecordedCapture();
}
private void backBtn_Click(object sender, RoutedEventArgs e)
{
if (Frame.CanGoBack)
{
Frame.GoBack();
}
}
}
}
Any help or guidance in resolving these errors would be greatly appreciated,
Thanks

The original Accord.NET Framework is not accessible on other platforms than .NET.
There is an effort (of which I am responsible) for porting Accord.NET to mobile platforms via Portable Class Libraries. Several of these packages have been published on NuGet as well (prefix Portable Accord).
The Audio package is not published on NuGet, but you should be able to build it from source for Windows Phone 8.1. You can find the source for Portable Accord here.
Please note that only playback is supported, recording is not.

need help on button to switch on webcam for C# based QR code project

i am currently learning on QR code webcam decoder. i have taken an example from https://zxingnet.svn.codeplex.com/svn/trunk/Clients/AForgeDemo/ and have succesfully build it without error. however when i run it with my webcam connected, no input or it wont switch on the webcam. based on my understanding, the webcam would be switch on when user select it at combobox. well, since there is no error at build, i cant pinpoint what went wrong. i have also taken a look at a project which switch on the webcam when user press a button and i plan to implement it to the current project. i have already insert the button but i do not know what should i program at the button to switch on the webcam instead on having to choose at combobox
would someone kindly advise or guide me through it.
below is the main program, and 2 class
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 AForge.Video;
using ZXing;
using System.Threading;
namespace AForgeDemo
{
public partial class AForgeDemoForm : Form
{
private struct Device
{
public int Index;
public string Name;
public override string ToString()
{
return Name;
}
}
private readonly CameraDevices camDevices;
private Bitmap currentBitmapForDecoding;
private readonly Thread decodingThread;
private Result currentResult;
private readonly Pen resultRectPen;
public AForgeDemoForm()
{
InitializeComponent();
camDevices = new CameraDevices();
decodingThread = new Thread(DecodeBarcode);
decodingThread.Start();
pictureBox1.Paint += pictureBox1_Paint;
resultRectPen = new Pen(Color.Green, 10);
}
void pictureBox1_Paint(object sender, PaintEventArgs e)
{
if (currentResult == null)
return;
if (currentResult.ResultPoints != null && currentResult.ResultPoints.Length > 0)
{
var resultPoints = currentResult.ResultPoints;
var rect = new Rectangle((int)resultPoints[0].X, (int)resultPoints[0].Y, 1, 1);
foreach (var point in resultPoints)
{
if (point.X < rect.Left)
rect = new Rectangle((int)point.X, rect.Y, rect.Width + rect.X - (int)point.X, rect.Height);
if (point.X > rect.Right)
rect = new Rectangle(rect.X, rect.Y, rect.Width + (int)point.X - rect.X, rect.Height);
if (point.Y < rect.Top)
rect = new Rectangle(rect.X, (int)point.Y, rect.Width, rect.Height + rect.Y - (int)point.Y);
if (point.Y > rect.Bottom)
rect = new Rectangle(rect.X, rect.Y, rect.Width, rect.Height + (int)point.Y - rect.Y);
}
using (var g = pictureBox1.CreateGraphics())
{
g.DrawRectangle(resultRectPen, rect);
}
}
}
protected override void OnLoad(EventArgs e)
{
base.OnLoad(e);
LoadDevicesToCombobox();
}
protected override void OnClosing(System.ComponentModel.CancelEventArgs e)
{
base.OnClosing(e);
if (!e.Cancel)
{
decodingThread.Abort();
if (camDevices.Current != null)
{
camDevices.Current.NewFrame -= Current_NewFrame;
if (camDevices.Current.IsRunning)
{
camDevices.Current.SignalToStop();
}
}
}
}
private void LoadDevicesToCombobox()
{
cmbDevice.Items.Clear();
for (var index = 0; index < camDevices.Devices.Count; index++)
{
cmbDevice.Items.Add(new Device { Index = index, Name = camDevices.Devices[index].Name });
}
}
private void cmbDevice_SelectedIndexChanged(object sender, EventArgs e)
{
if (camDevices.Current != null)
{
camDevices.Current.NewFrame -= Current_NewFrame;
if (camDevices.Current.IsRunning)
{
camDevices.Current.SignalToStop();
}
}
camDevices.SelectCamera(((Device)(cmbDevice.SelectedItem)).Index);
camDevices.Current.NewFrame += Current_NewFrame;
camDevices.Current.Start();
}
private void Current_NewFrame(object sender, NewFrameEventArgs eventArgs)
{
if (IsDisposed)
{
return;
}
try
{
if (currentBitmapForDecoding == null)
{
currentBitmapForDecoding = (Bitmap)eventArgs.Frame.Clone();
}
Invoke(new Action<Bitmap>(ShowFrame), eventArgs.Frame.Clone());
}
catch (ObjectDisposedException)
{
// not sure, why....
}
}
private void ShowFrame(Bitmap frame)
{
if (pictureBox1.Width < frame.Width)
{
pictureBox1.Width = frame.Width;
}
if (pictureBox1.Height < frame.Height)
{
pictureBox1.Height = frame.Height;
}
pictureBox1.Image = frame;
}
private void DecodeBarcode()
{
var reader = new BarcodeReader();
while (true)
{
if (currentBitmapForDecoding != null)
{
var result = reader.Decode(currentBitmapForDecoding);
if (result != null)
{
Invoke(new Action<Result>(ShowResult), result);
}
currentBitmapForDecoding.Dispose();
currentBitmapForDecoding = null;
}
Thread.Sleep(200);
}
}
private void ShowResult(Result result)
{
currentResult = result;
txtBarcodeFormat.Text = result.BarcodeFormat.ToString();
txtContent.Text = result.Text;
}
private void button1_Click(object sender, EventArgs e)
{
}
}
}
the class for cameradevice
using System.Collections.Generic;
using System.Linq;
using System.Text;
using AForge.Video.DirectShow;
namespace AForgeDemo
{
internal class CameraDevices
{
public FilterInfoCollection Devices { get; private set; }
public VideoCaptureDevice Current { get; private set; }
public CameraDevices()
{
Devices = new FilterInfoCollection(FilterCategory.VideoInputDevice);
}
public void SelectCamera(int index)
{
if (index >= Devices.Count)
{
throw new ArgumentOutOfRangeException("index");
}
Current = new VideoCaptureDevice(Devices[index].MonikerString);
}
}
}
again, i kindly ask for anybody help on what i shall put at the button command to activate the webcam directly instead of choosing from combobox
thanks a million

The code which you need for your event handler behind the button is similar to the code within the method cmbDevice_SelectedIndexChanged.
I think it should look like the following
// select the first available camera and start capturing
camDevices.SelectCamera(0);
camDevices.Current.NewFrame += Current_NewFrame;
camDevices.Current.Start();
But I think the main challenge is to find out why the original example doesn't work as expected. It makes no difference if the same code is called in the handler of the combobox or in the handler of the button.