Develop Reference

Background Service run continuously in Xamarin Forms

i'm new with xamarin forms. I'm writing an app and i need to create a function that allow call api continuously to check the change of data, if have any change, i will handle something.
I'm looking for the solution but nothing, please help me :(
Thread is an idea?

Okay so first of all you need to poll the API in order to receive the data that you need to check. To do this you can implement my PollingTimer.cs class:
using System;
using System.Threading;
using Xamarin.Forms;
namespace CryptoTracker.Helpers
{
/// <summary>
/// This timer is used to poll the middleware for new information.
/// </summary>
public class PollingTimer
{
private readonly TimeSpan timespan;
private readonly Action callback;
private CancellationTokenSource cancellation;
/// <summary>
/// Initializes a new instance of the <see cref="T:CryptoTracker.Helpers.PollingTimer"/> class.
/// </summary>
/// <param name="timespan">The amount of time between each call</param>
/// <param name="callback">The callback procedure.</param>
public PollingTimer(TimeSpan timespan, Action callback)
{
this.timespan = timespan;
this.callback = callback;
this.cancellation = new CancellationTokenSource();
}
/// <summary>
/// Starts the timer.
/// </summary>
public void Start()
{
CancellationTokenSource cts = this.cancellation; // safe copy
Device.StartTimer(this.timespan,
() => {
if (cts.IsCancellationRequested) return false;
this.callback.Invoke();
return true; // or true for periodic behavior
});
}
/// <summary>
/// Stops the timer.
/// </summary>
public void Stop()
{
Interlocked.Exchange(ref this.cancellation, new CancellationTokenSource()).Cancel();
}
}
}
Now that you have added a polling timer to your project, you must now go to the content page that you wish to poll from. Here is the pseudo code for what your content page should look like:
namespace YourApp.Views
{
public class MainPage : ContentPage
{
PollingTimer timer;
public MainPage ()
{
//PUT UI CODE HERE
Content = layout;
//Instantiate Polling timer to call handleaction every 5 seconds
timer = new PollingTimer(TimeSpan.FromSeconds(5), HandleAction);
}
/// <summary>
/// When the page enters the users view, this procedure is called.
/// </summary>
protected override void OnAppearing()
{
base.OnAppearing();
//Handle action and start your timer
HandleAction();
timer.Start();
}
/// <summary>
/// When the page disappears from the users view this procedure is called.
/// </summary>
protected override void OnDisappearing()
{
base.OnDisappearing();
//Stop your timer
timer.Stop(); //Stop the timer
}
/// <summary>
/// Callback for the timer.
/// </summary>
void HandleAction()
{
//Make call to your api to get data
//Compare data with data you currently have
// Do whatever you want.
}
I hope this helps you. Let me know if you need any more help :)

You can use Timer Class for you issue.

Authenticate_Execute event override in Kentico CMS v8.2

I need to convert a Kentico 7 web application to Kentico 8.0.21. The old code has a CMSModuleLoader file in the App_Code folder which has code for Authenticate_Execute event.
The init event suggested by kentico does not get fired
public partial class CMSModuleLoader
{
private class AuthenticationHandler : CMSLoaderAttribute
{
/// <summary>
/// Called automatically when the application starts
/// </summary>
public override void Init()
{
// Assigns a handler to the SecurityEvents.Authenticate.Execute event
// This event occurs when users attempt to log in on the website
SecurityEvents.Authenticate.Execute += OnAuthentication;
}
private void OnAuthentication(object sender, AuthenticationEventArgs args)
{
if (args.User != null) //the authenticate was successful
{
try
{
var accountFacade = WebContainer.Instance.Container.GetInstance<IAccountFacade>();
accountFacade.ReconcileOnLogin(args.UserName);
}
catch (Exception e)
{
var logger = LogManager.GetCurrentClassLogger();
var ex = new Exception("IAccountFacade.ReconcileOnLogin method throw an error communicating with dynamics, the issue is not resolvable from Kentico thus regardless of the permission level of the current user, the exception will be bubbled up and the user will be shown error details or the custom error page.", e);
logger.Fatal(x => x("The current exception is caused by dynamics/data problems and the user will not be allowed to login. A system admin with access to dynamics is required to resolve the problem.", e));
throw ex;
}
//ResetPasswordAttempts(args.User);
}
}
}
/// <summary>
/// Attribute class that ensures the loading of custom handlers
/// </summary>
private class CustomSecurityEventsAttribute : CMS.Base.CMSLoaderAttribute
{
/// <summary>
/// Called automatically when the application starts
/// </summary>
public override void Init()
{
SecurityEvents.Authenticate.Execute += new EventHandler<AuthenticationEventArgs>(Authenticate_Execute);
}
/// <summary>
/// called on every kentico authenticate attempt
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>

All authentication-related events were moved to CMS.Membership.SecurityEvents in Kentico 8.0. The usage is as follows:
using System.Data;
using CMS.Base;
using CMS.Membership;
using CMS.DataEngine;
[AuthenticationHandler]
public partial class CMSModuleLoader
{
/// <summary>
/// Custom attribute class.
/// </summary>
private class AuthenticationHandler : CMSLoaderAttribute
{
/// <summary>
/// Called automatically when the application starts
/// </summary>
public override void Init()
{
// Assigns a handler to the SecurityEvents.Authenticate.Execute event
// This event occurs when users attempt to log in on the website
SecurityEvents.Authenticate.Execute += OnAuthentication;
}
}
}
For more info refer to the documentation.

How to make a render loop in WPF?

How can I create a loop that will be continuously executed whenever the message loop is idle in WPF?
The goal here is to perform some long running graphical update, such as refreshing a PicktureBox, that is capable of consuming whatever free resources are available but shouldn't freeze the UI or otherwise take priority over any other operations in the message queue.
I noticed this blog post which provides the code to do this in a winforms application, but I don't know how to translate it to a WPF application. Below is the code of a WinForms render loop class that I made based on the other article:
using System;
using System.Runtime.InteropServices;
using System.Threading;
using System.Windows.Forms;
namespace Utilities.UI
{
/// <summary>
/// WinFormsAppIdleHandler implements a WinForms Render Loop (max FPS possible).
/// Reference: http://blogs.msdn.com/b/tmiller/archive/2005/05/05/415008.aspx
/// </summary>
public sealed class WinFormsAppIdleHandler
{
private readonly object _completedEventLock = new object();
private event EventHandler _applicationLoopDoWork;
//PRIVATE Constructor
private WinFormsAppIdleHandler()
{
Enabled = false;
SleepTime = 10;
Application.Idle += Application_Idle;
}
/// <summary>
/// Singleton from:
/// http://csharpindepth.com/Articles/General/Singleton.aspx
/// </summary>
private static readonly Lazy<WinFormsAppIdleHandler> lazy = new Lazy<WinFormsAppIdleHandler>(() => new WinFormsAppIdleHandler());
public static WinFormsAppIdleHandler Instance { get { return lazy.Value; } }
/// <summary>
/// Gets or sets if must fire ApplicationLoopDoWork event.
/// </summary>
public bool Enabled { get; set; }
/// <summary>
/// Gets or sets the minimum time betwen ApplicationLoopDoWork fires.
/// </summary>
public int SleepTime { get; set; }
/// <summary>
/// Fires while the UI is free to work. Sleeps for "SleepTime" ms.
/// </summary>
public event EventHandler ApplicationLoopDoWork
{
//Reason of using locks:
//http://stackoverflow.com/questions/1037811/c-thread-safe-events
add
{
lock (_completedEventLock)
_applicationLoopDoWork += value;
}
remove
{
lock (_completedEventLock)
_applicationLoopDoWork -= value;
}
}
/// <summary>
/// FINALMENTE! Imagem ao vivo sem travar! Muito bom!
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
private void Application_Idle(object sender, EventArgs e)
{
//Try to update interface
while (Enabled && IsAppStillIdle())
{
OnApplicationIdleDoWork(EventArgs.Empty);
//Give a break to the processor... :)
//8 ms -> 125 Hz
//10 ms -> 100 Hz
Thread.Sleep(SleepTime);
}
}
private void OnApplicationIdleDoWork(EventArgs e)
{
var handler = _applicationLoopDoWork;
if (handler != null)
{
handler(this, e);
}
}
/// <summary>
/// Gets if the app still idle.
/// </summary>
/// <returns></returns>
private static bool IsAppStillIdle()
{
bool stillIdle = false;
try
{
Message msg;
stillIdle = !PeekMessage(out msg, IntPtr.Zero, 0, 0, 0);
}
catch (Exception e)
{
//Should never get here... I hope...
MessageBox.Show("IsAppStillIdle() Exception. Message: " + e.Message);
}
return stillIdle;
}
#region Unmanaged Get PeekMessage
// http://blogs.msdn.com/b/tmiller/archive/2005/05/05/415008.aspx
[System.Security.SuppressUnmanagedCodeSecurity] // We won't use this maliciously
[DllImport("User32.dll", CharSet = CharSet.Auto)]
public static extern bool PeekMessage(out Message msg, IntPtr hWnd, uint messageFilterMin, uint messageFilterMax, uint flags);
#endregion
}
}

The best way to do this is to use the per-frame callbacks provided by the static CompositionTarget.Rendering event.

To elaborate a bit on the answer of Oren, you can attach a method to the Rendering event like this:
CompositionTarget.Rendering += Loop;
The Loop function can then update the properties of an element, in this example an element positioned on a Canvas:
private void Loop(object sender, EventArgs e)
{
LeftPos++;
Canvas.SetLeft(ball, LeftPos);
}
https://learn.microsoft.com/en-us/dotnet/api/system.windows.media.compositiontarget.rendering?view=net-5.0

Syncing between multiple instances of the same program

I have quite a complicated programming problem on my hands, so bear with me for a few minutes.
I decided i want to create a media player in WPF (C#) and i've run into a bit of a pickle.
I want my application to be single instance, so that when the user double clicks server files, the program would only run once and queue all files for playing.
I tried several ways of doing it, including Microsoft's single instance implementation, and nothing seemed to work, until i decided to create my own, as in i though of something and implemented it (this probably was on the internet somewhere as well, but it didn't show up)
Basically, i use a named mutex to prevent more than one instance from being opened, and to force the other instances to write their arguments to a file, and after that, the instance which created the mutex would read the file.
Needless to say, this is very, very ineffective as far as performance goes, but anyway, here is my implementation of the Main() function.
Note that this Main() is also written from scratch, as i didn't really like the one automatically generated by the VS2010.
static void Main(string[] args)
{
string[] arguments = new string[0];
handler g = new handler();
bool createdNew = false;
Mutex lolpaca = new Mutex(true, "lolpacamaximumtrolololololol", out createdNew);
if (createdNew)
{
if (args != null)
{
var MainWindow = new MainWindow();
var app = new Application();
app.Run(MainWindow);
lolpaca.ReleaseMutex();
lolpaca.Dispose();
}
else
{
Array.Resize(ref arguments, 1);
arguments[0] = args[0];
string line;
//nu mai arunca exceptii nenorocitule
while ((line = g.ReadArgs()) != null)
{
int old_size = arguments.Length;
Array.Resize(ref arguments, arguments.Length + 1);
arguments[old_size] = line;
}
var MainWindow = new MainWindow(arguments, arguments.Length);
var app = new Application();
app.Run(MainWindow);
lolpaca.ReleaseMutex();
lolpaca.Dispose();
}
if (File.Exists(path))
{
File.Delete(path);
}
}
else
{
Thread writer = new Thread(new ParameterizedThreadStart(g.WriteArg));
writer.Start(args);
writer.Join();
try
{
g.WriteArg(args);
}
catch (IOException e)
{
MediaPlayerFinal_GUI_new.ExceptionCatcher exp = new MediaPlayerFinal_GUI_new.ExceptionCatcher(e.Source);
exp.Show();
}
}
}
I'm also using this class to attempt to sync between the threads
public class handler
{
static string path = #"D:\playlist.txt";
static FileStream fs = new FileStream(path, FileMode.Open, FileAccess.ReadWrite, FileShare.ReadWrite);
string line;
string arg;
bool readerFlag = false;
public string ReadArgs()
{
try
{
lock (fs) // Enter synchronization block
{
if (!readerFlag)
{ // Wait until writer finishes
try
{
// Waits for the Monitor.Pulse in WriteArg
Monitor.Wait(fs);
}
catch (SynchronizationLockException)
{
}
catch (ThreadInterruptedException)
{
}
}
TextReader tr = new StreamReader(fs);
while ((line = tr.ReadLine()) != null)
{
arg = line;
}
tr.Close();
tr.Dispose();
}
/* fs.Close();
fs.Dispose();*/
readerFlag = false;
Monitor.Pulse(fs);
return arg;
}
catch (IOException e)
{
MediaPlayerFinal_GUI_new.ExceptionCatcher exp = new MediaPlayerFinal_GUI_new.ExceptionCatcher(e.Source);
exp.Show();
return null;
}
}
public void WriteArg(object args)
{
lock (fs)
{
try
{
if (readerFlag)
{
try
{
Monitor.Wait(fs); // Wait for the Monitor.Pulse in ReadArgs
}
catch (SynchronizationLockException)
{
}
catch (ThreadInterruptedException)
{
}
}
arg = Convert.ToString(args);
// FileStream fs = new FileStream(path, FileMode.Append, FileAccess.Write, FileShare.Read);
TextWriter tw = new StreamWriter(fs);
tw.WriteLine(args);
tw.Close();
tw.Dispose();
}
catch (IOException e)
{
MediaPlayerFinal_GUI_new.ExceptionCatcher exp = new MediaPlayerFinal_GUI_new.ExceptionCatcher(e.Source);
exp.Show();
}
}
/* fs.Close();
fs.Dispose();*/
readerFlag = true;
Monitor.Pulse(fs);
}
}
Now, basically, for each double clicked file, one instance of the Main() function is created by Windows.
The first instance has control over the mutex and proceeds to doing whatever it wants to do.
The other instances must write their argument to the file.
Now, the problem:
Apparently, the threads (all of them) do no sync properly, and sometimes i get IO exceptions.
I have no clue where exactly these exceptions are thrown, because the try-catch blocks seem to do exactly nothing. In fact, I believe this is a little deeper than try-catch would work on.
So, how do i sync all the threads that spawn when the user double clicks a lot of files? This implementation works ok with up to 3 double clicked files, and sometimes (note, sometimes it works, other times it doesn't) with more than 3 files (tested with up to 9).
Nothing i found so far on the internet accounts for several instances of the same application running independently.
It would be great if you could give me an example:)
Thank you.

The best way to talk between two instances of the same application is use IPC. Bellow see example of class that can be used to help with single instance:
/// <summary>
/// Enforces single instance for an application.
/// </summary>
public class SingleInstance : IDisposable
{
#region Fields
/// <summary>
/// The synchronization context.
/// </summary>
private readonly SynchronizationContext synchronizationContext;
/// <summary>
/// The disposed.
/// </summary>
private bool disposed;
/// <summary>
/// The identifier.
/// </summary>
private Guid identifier = Guid.Empty;
/// <summary>
/// The mutex.
/// </summary>
private Mutex mutex;
#endregion
#region Constructors and Destructors
/// <summary>
/// Initializes a new instance of the <see cref="SingleInstance"/> class.
/// </summary>
/// <param name="identifier">
/// An identifier unique to this application.
/// </param>
/// <param name="args">
/// The command line arguments.
/// </param>
public SingleInstance(Guid identifier, IEnumerable<string> args)
{
this.identifier = identifier;
bool ownsMutex;
this.mutex = new Mutex(true, identifier.ToString(), out ownsMutex);
this.synchronizationContext = SynchronizationContext.Current;
this.FirstInstance = ownsMutex;
if (this.FirstInstance)
{
this.ListenAsync();
}
else
{
this.NotifyFirstInstance(args);
}
}
/// <summary>
/// Initializes a new instance of the <see cref="SingleInstance"/> class.
/// </summary>
/// <param name="identifier">
/// An identifier unique to this application.
/// </param>
public SingleInstance(Guid identifier)
: this(identifier, null)
{
}
#endregion
#region Public Events
/// <summary>
/// Event raised when arguments are received from successive instances.
/// </summary>
public event EventHandler<OtherInstanceCreatedEventArgs> OtherInstanceCreated;
#endregion
#region Public Properties
/// <summary>
/// Gets a value indicating whether this is the first instance of this application.
/// </summary>
public bool FirstInstance { get; private set; }
#endregion
#region Implemented Interfaces
#region IDisposable
/// <summary>
/// The dispose.
/// </summary>
public void Dispose()
{
this.Dispose(true);
GC.SuppressFinalize(this);
}
#endregion
#endregion
#region Methods
/// <summary>
/// Clean up any resources being used.
/// </summary>
/// <param name="disposing">
/// True if managed resources should be disposed; otherwise, false.
/// </param>
protected virtual void Dispose(bool disposing)
{
if (this.disposed)
{
return;
}
if (disposing)
{
if (this.mutex != null && this.FirstInstance)
{
this.mutex.WaitOne();
this.mutex.ReleaseMutex();
this.mutex = null;
}
}
this.disposed = true;
}
/// <summary>
/// Fires the OtherInstanceCreated event.
/// </summary>
/// <param name="arguments">
/// The arguments to pass with the <see cref="OtherInstanceCreatedEventArgs"/> class.
/// </param>
protected virtual void OnOtherInstanceCreated(OtherInstanceCreatedEventArgs arguments)
{
EventHandler<OtherInstanceCreatedEventArgs> handler = this.OtherInstanceCreated;
if (handler != null)
{
handler(this, arguments);
}
}
/// <summary>
/// Listens for arguments on a named pipe.
/// </summary>
private void Listen()
{
try
{
using (var server = new NamedPipeServerStream(this.identifier.ToString()))
{
using (var reader = new StreamReader(server))
{
server.WaitForConnection();
var arguments = new List<string>();
while (server.IsConnected)
{
arguments.Add(reader.ReadLine());
}
this.synchronizationContext.Post(o => this.OnOtherInstanceCreated(new OtherInstanceCreatedEventArgs(arguments)), null);
}
}
// start listening again.
this.Listen();
}
catch (IOException)
{
// Pipe was broken, listen again.
this.Listen();
}
}
/// <summary>
/// Listens for arguments being passed from successive instances of the applicaiton.
/// </summary>
private void ListenAsync()
{
Task.Factory.StartNew(this.Listen, TaskCreationOptions.LongRunning);
}
/// <summary>
/// Passes the given arguments to the first running instance of the application.
/// </summary>
/// <param name="arguments">
/// The arguments to pass.
/// </param>
private void NotifyFirstInstance(IEnumerable<string> arguments)
{
try
{
using (var client = new NamedPipeClientStream(this.identifier.ToString()))
{
using (var writer = new StreamWriter(client))
{
client.Connect(200);
if (arguments != null)
{
foreach (string argument in arguments)
{
writer.WriteLine(argument);
}
}
}
}
}
catch (TimeoutException)
{
// Couldn't connect to server
}
catch (IOException)
{
// Pipe was broken
}
}
#endregion
}
/// <summary>
/// Holds a list of arguments given to an application at startup.
/// </summary>
public class OtherInstanceCreatedEventArgs : EventArgs
{
#region Constructors and Destructors
/// <summary>
/// Initializes a new instance of the <see cref="OtherInstanceCreatedEventArgs"/> class.
/// </summary>
/// <param name="args">
/// The command line arguments.
/// </param>
public OtherInstanceCreatedEventArgs(IEnumerable<string> args)
{
this.Args = args;
}
#endregion
#region Public Properties
/// <summary>
/// Gets the startup arguments.
/// </summary>
public IEnumerable<string> Args { get; private set; }
#endregion
}
Then in your main class you can create instance of of class that will stay until aplication is running. You can check if other instance is created by FirstInstance property, And get notified of other instance created by OtherInstanceCreated event.

How to receive Plug & Play device notifications without a windows form

I am trying to write a class library that can catch the windows messages to notify me if a device has been attached or removed. Normally, in a windows forms app I would just override the WndProc method but there is not WndProc method in this case. Is there another way I can get the messages?

You'll need a window, there's no way around that. Here's a sample implementation. Implement an event handler for the DeviceChangeNotifier.DeviceNotify event to get notifications. Call the DeviceChangeNotifier.Start() method at the start of your program. Call DeviceChangeNotifier.Stop() at the end of your program. Beware that the DeviceNotify event is raised on a background thread, be sure to lock as needed to keep your code thread-safe.
using System;
using System.Windows.Forms;
using System.Threading;
class DeviceChangeNotifier : Form {
public delegate void DeviceNotifyDelegate(Message msg);
public static event DeviceNotifyDelegate DeviceNotify;
private static DeviceChangeNotifier mInstance;
public static void Start() {
Thread t = new Thread(runForm);
t.SetApartmentState(ApartmentState.STA);
t.IsBackground = true;
t.Start();
}
public static void Stop() {
if (mInstance == null) throw new InvalidOperationException("Notifier not started");
DeviceNotify = null;
mInstance.Invoke(new MethodInvoker(mInstance.endForm));
}
private static void runForm() {
Application.Run(new DeviceChangeNotifier());
}
private void endForm() {
this.Close();
}
protected override void SetVisibleCore(bool value) {
// Prevent window getting visible
if (mInstance == null) CreateHandle();
mInstance = this;
value = false;
base.SetVisibleCore(value);
}
protected override void WndProc(ref Message m) {
// Trap WM_DEVICECHANGE
if (m.Msg == 0x219) {
DeviceNotifyDelegate handler = DeviceNotify;
if (handler != null) handler(m);
}
base.WndProc(ref m);
}
}

I have a working USB communication class that implements device change notification in a slightly different way if anyone is interested. It's pretty compact (w/o the comments) and doesn't rely on Threading or the OnSourceInitialized and HwndHandler stuff in the client. Also, you do not need a Form or Window as mentioned. Any type where you can override WndProc() can be used. I use a Control.
The sample contains only code needed for notification and nothing else. The sample code is C++/CLI and although I don't subscribe to the practice of putting executable code in header files, for the sake of brevity, I do so here.
#pragma once
#include <Windows.h> // Declares required datatypes.
#include <Dbt.h> // Required for WM_DEVICECHANGE messages.
#include <initguid.h> // Required for DEFINE_GUID definition (see below).
namespace USBComms
{
using namespace System;
using namespace System::Runtime::InteropServices;
using namespace System::Windows;
using namespace System::Windows::Forms;
// This function is required for receieving WM_DEVICECHANGE messages.
// Note: name is remapped "RegisterDeviceNotificationUM"
[DllImport("user32.dll" , CharSet = CharSet::Unicode, EntryPoint="RegisterDeviceNotification")]
extern "C" HDEVNOTIFY WINAPI RegisterDeviceNotificationUM(
HANDLE hRecipient,
LPVOID NotificationFilter,
DWORD Flags);
// Generic guid for usb devices (see e.g. http://msdn.microsoft.com/en-us/library/windows/hardware/ff545972%28v=vs.85%29.aspx).
// Note: GUIDs are device and OS specific and may require modification. Using the wrong guid will cause notification to fail.
// You may have to tinker with your device to find the appropriate GUID. "hid.dll" has a function `HidD_GetHidGuid' that returns
// "the device interfaceGUID for HIDClass devices" (see http://msdn.microsoft.com/en-us/library/windows/hardware/ff538924%28v=vs.85%29.aspx).
// However, testing revealed it does not always return a useful value. The GUID_DEVINTERFACE_USB_DEVICE value, defined as
// {A5DCBF10-6530-11D2-901F-00C04FB951ED}, has worked with cell phones, thumb drives, etc. For more info, see e.g.
// http://msdn.microsoft.com/en-us/library/windows/hardware/ff553426%28v=vs.85%29.aspx.
DEFINE_GUID(GUID_DEVINTERFACE_USB_DEVICE, 0xA5DCBF10L, 0x6530, 0x11D2, 0x90, 0x1F, 0x00, 0xC0, 0x4F, 0xB9, 0x51, 0xED);
/// <summary>
/// Declare a delegate for the notification event handler.
/// </summary>
/// <param name="sender">The object where the event handler is attached.</param>
/// <param name="e">The event data.</param>
public delegate void NotificationEventHandler(Object^ sender, EventArgs^ e);
/// <summary>
/// Class that generetaes USB Device Change notification events.
/// </summary>
/// <remarks>
/// A Form is not necessary. Any type wherein you can override WndProc() can be used.
/// </remarks>
public ref class EventNotifier : public Control
{
private:
/// <summary>
/// Raises the NotificationEvent.
/// </summary>
/// <param name="e">The event data.</param>
void RaiseNotificationEvent(EventArgs^ e) {
NotificationEvent(this, e);
}
protected:
/// <summary>
/// Overrides the base class WndProc method.
/// </summary>
/// <param name="message">The Windows Message to process. </param>
/// <remarks>
/// This method receives Windows Messages (WM_xxxxxxxxxx) and
/// raises our NotificationEvent as appropriate. Here you should
/// add any message filtering (e.g. for the WM_DEVICECHANGE) and
/// preprocessing before raising the event (or not).
/// </remarks>
virtual void WndProc(Message% message) override {
if(message.Msg == WM_DEVICECHANGE)
{
RaiseNotificationEvent(EventArgs::Empty);
}
__super::WndProc(message);
}
public:
/// <summary>
/// Creates a new instance of the EventNotifier class.
/// </summary>
EventNotifier(void) {
RequestNotifications(this->Handle); // Register ourselves as the Windows Message processor.
}
/// <summary>
/// Registers an object, identified by the handle, for
/// Windows WM_DEVICECHANGE messages.
/// </summary>
/// <param name="handle">The object's handle.</param>
bool RequestNotifications(IntPtr handle) {
DEV_BROADCAST_DEVICEINTERFACE NotificationFilter;
ZeroMemory(&NotificationFilter, sizeof(NotificationFilter));
NotificationFilter.dbcc_devicetype = DBT_DEVTYP_DEVICEINTERFACE;
NotificationFilter.dbcc_size = sizeof(DEV_BROADCAST_DEVICEINTERFACE);
NotificationFilter.dbcc_reserved = 0;
NotificationFilter.dbcc_classguid = GUID_DEVINTERFACE_USB_DEVICE;
return RegisterDeviceNotificationUM((HANDLE)handle, &NotificationFilter, DEVICE_NOTIFY_WINDOW_HANDLE) != NULL;
}
/// <summary>
/// Defines the notification event.
/// </summary>
virtual event NotificationEventHandler^ NotificationEvent;
};
}
Then, in the 'receiver' (the object that subscribes to and consumes our NotificationEvent), all you have to do is:
void Receiver::SomeFunction(void)
{
USBComms::EventNotifier usb = gcnew USBComms::EventNotifier();
usb->NotificationEvent += gcnew USBComms::NotificationEventHandler(this, &Receiver::USBEvent);
}
void Receiver::USBEvent(Object^ sender, EventArgs^ e)
{
// Handle the event notification as appropriate.
}

In Windows CE / Windows Mobile / SmartDevice projects, the standard Form does not provide an override to the WndProc method, but this can be accomplished by making a class based on Microsoft.WindowsCE.Forms.MessageWindow, creating a constructor that takes a form, hold that form in a local variable so that a method on that form can be called whenever the message is detected. Here's a scaled down sample to illustrate. Hope this is helpful to someone in the CE / Windows Mobile world.
public class MsgWindow : Microsoft.WindowsCE.Forms.MessageWindow {
public const int WM_SER = 0x500;
public const int WM_SER_SCANDONE = WM_SER + 0;
frmMain msgform { get; set; }
public MsgWindow(frmMain msgform) {
this.msgform = msgform;
}
protected override void WndProc(ref Microsoft.WindowsCE.Forms.Message m) {
switch (m.Msg) {
case WM_SER_SCANDONE:
this.msgform.RespondToMessage(WM_SER_SCANDONE);
break;
default:
break;
}
base.WndProc(ref m);
}
}
public partial class frmMain : Form {
public frmMain() {
InitializeComponent();
}
public void RespondToMessage(int nMsg) {
try {
switch (nMsg) {
case MsgWindow.WM_SER_SCANDONE:
// do something here based on the message
break;
default:
break;
}
} catch (Exception ex) {
MessageBox.Show(string.Format("{0} - {1}", ex.Message, ex.ToString()), "RespondToMessage() Error", MessageBoxButtons.OK, MessageBoxIcon.Exclamation, MessageBoxDefaultButton.Button1);
// throw;
}
}
}