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Multiple generic event publishers?

I have this simple interface:
public interface IEventPublisher<T>
{
public delegate void EventHandler(T report);
public event EventHandler OnEventReceived;
}
Then I can write a class to subscribe to events of type int and string:
public class Subscriber
{
public Subscriber(IEventPublisher<int> intPublisher, IEventPublisher<string> stringPublisher)
{
intPublisher.OnEventReceived += OnIntEventReceived;
stringPublisher.OnEventReceived += OnStringEventReceived;
}
private void OnIntEventReceived(int report)
{
}
private void OnStringEventReceived(string report)
{
}
}
Now comes the challenge: I would like to write a class to be a publisher of events of type int and string, so I start with:
public class Publisher : IEventPublisher<int>, IEventPublisher<string>
{
}
How do I implement this in order to satisfy both interfaces? The problem is that the event handler names are identical (OnEventReceived).
This is how I would have written it for a publisher just implementing one of the interfaces:
public interface IEventPublisher<T>
{
public delegate void EventHandler(T report);
public event EventHandler OnEventReceived;
}
public class Subscriber
{
public Subscriber(IEventPublisher<int> intPublisher)
{
intPublisher.OnEventReceived += OnIntEventReceived;
}
private void OnIntEventReceived(int report)
{
}
}
public class Publisher : IEventPublisher<int>
{
public event IEventPublisher<int>.EventHandler? OnEventReceived;
public Publisher()
{
Subscriber subscriber = new Subscriber(this);
}
private void GenerateEvents()
{
while (true)
{
...
OnEventReceived?.Invoke(number);
}
}
}

Did you try it? My IDE (with ReSharper) gives this implementation:
public class Publisher : IEventPublisher<int>, IEventPublisher<string>
{
event IEventPublisher<int>.EventHandler? IEventPublisher<int>.OnEventReceived
{
add
{
// Your code here.
}
remove
{
// Your code here.
}
}
event IEventPublisher<string>.EventHandler? IEventPublisher<string>.OnEventReceived
{
add
{
// Your code here.
}
remove
{
// Your code here.
}
}
}
And the Subscriber class would subscribe like this.
public class Subscriber
{
public Subscriber()
{
var publisher = new Publisher();
IEventPublisher<int> intPublisher = publisher;
IEventPublisher<string> stringPublisher = publisher;
intPublisher.OnEventReceived += OnIntEventReceived;
stringPublisher.OnEventReceived += OnStringEventReceived;
}
private void OnIntEventReceived(int report)
{
}
private void OnStringEventReceived(string report)
{
}
}
Note: I haven't actually tried compiling/running this.

Assign event and function in extension method as argument

I have a list of objects and I want to assign values in a factory method. I have checked similar questions but they have access to a method in existing assembly. I want to use a custom method and also define which event should be set.
for example
mylist.Assign(nameofevent,assignfuntion);
the usage something like
public static void Assign(this Control[] controls,eventhandler #event,Action func)
{
foreach (var item in controls)
//assign function to event
item.clicked += func;//Preferably clicked must be Specified from argument
}

Trying to help to get to the bottom of what is wrong with Shervin Ivari's question. I'm illustration how you can achieve it. But still unsure if this is what you want?
public static void Main()
{
var listeners = new List<SomeClassWithListener>
{
new SomeClassWithListener(),
new SomeClassWithListener(),
new SomeClassWithListener()
};
var theEvent = new SomeClassWithEvent();
MatchEmUp(listeners, theEvent);
theEvent.RaiseEvent();
}
public static void MatchEmUp(IEnumerable<SomeClassWithListener> listeners, SomeClassWithEvent theEvent)
{
foreach(SomeClassWithListener listener in listeners)
theEvent.ItsAlive += listener.ThenIllSlayIt;
}
public class SomeClassWithListener
{
public void ThenIllSlayIt(object sender, EventArgs e)
{
Console.WriteLine("Chaaaaaarge!");
}
}
public class SomeClassWithEvent
{
public EventHandler ItsAlive;
public void RaiseEvent()
{
ItsAlive.Invoke(this, new EventArgs());
}
}
https://dotnetfiddle.net/4Y13cf
Or by using delegates, EventHandler is also a delegate:
public static void Main()
{
var listener1 = new SomeClassWithListener();
var listener2 = new SomeClassWithListener();
var listener3 = new SomeClassWithListener();
var listeners = new List<EventHandler>
{
listener1.ThenIllSlayIt,
listener2.ThenIllSlayIt,
listener3.ThenIllSlayIt
};
var theEvent = new SomeClassWithEvent();
MatchEmUp(listeners, theEvent);
theEvent.RaiseEvent();
}
public static void MatchEmUp(IEnumerable<EventHandler> listeners, SomeClassWithEvent theEvent)
{
foreach(EventHandler listener in listeners)
theEvent.ItsAlive += listener;
}
public class SomeClassWithListener
{
public void ThenIllSlayIt(object sender, EventArgs e)
{
Console.WriteLine("Chaaaaaarge!");
}
}
public class SomeClassWithEvent
{
public EventHandler ItsAlive;
public void RaiseEvent()
{
ItsAlive.Invoke(this, new EventArgs());
}
}
https://dotnetfiddle.net/k16lsy

Why is a "forwarded" event not raised when assigning a method group but is when assigning a delegate?

Given the following code:
public delegate void Signal();
public static class SignalExtensions
{
public static void SafeInvoke(this Signal signal)
{
Signal copy = signal;
if (copy != null)
{
copy();
}
}
}
public class RootEventSource
{
public event Signal RootEvent;
public void Raise()
{
this.RootEvent.SafeInvoke();
}
}
public class EventForwarder
{
private readonly RootEventSource rootEventSource;
public EventForwarder(RootEventSource rootEventSource)
{
this.rootEventSource = rootEventSource;
// this is the critical part
this.rootEventSource.RootEvent
+= () => this.AnotherEvent.SafeInvoke();
}
public event Signal AnotherEvent;
// just an example of another method which is using the root event source
public override string ToString()
{
return this.rootEventSource.ToString();
}
}
class Program
{
static void Main(string[] args)
{
var rootEventSource = new RootEventSource();
var eventForwarder = new EventForwarder(rootEventSource);
eventForwarder.AnotherEvent += HandleAnotherEvent;
rootEventSource.Raise();
Console.WriteLine("done");
Console.ReadKey();
}
private static void HandleAnotherEvent()
{
Console.WriteLine("received AnotherEvent");
}
}
This results in the output:
received AnotherEvent
done
Now I make a slight change to the implementation of EventForwarder to use a method group for forwarding the event:
public EventForwarder(RootEventSource rootEventSource)
{
this.rootEventSource = rootEventSource;
this.rootEventSource.RootEvent += this.AnotherEvent.SafeInvoke;
}
The output becomes:
done
So AnotherEvent is not raised.
Until now i would have considered the two lines:
this.rootEventSource.RootEvent += this.AnotherEvent.SafeInvoke;
this.rootEventSource.RootEvent += () => this.AnotherEvent.SafeInvoke();
as being equivalent. It seems they're not.
So what is the difference? Plus why is the event not being raised?
PS: while usually R# suggests to replace () => this.AnotherEvent.SafeInvoke(); by this.AnotherEvent.SafeInvoke it doesn't do so here. So apparently it knows that it should not do it here.

When you assign a method group to event like this:
this.rootEventSource.RootEvent += this.AnotherEvent.SafeInvoke;
you in fact create a delegate from method SignalExtensions.SafeInvoke which as a parameter takes your this.AnotherEventdelegate object. Since it is initially null, you create a delegate with null parameter. This null value will of course never change, since delegates are immutable.
If you want to forward an event you should maybe do it like this:
public class EventForwarder
{
private readonly RootEventSource rootEventSource;
public EventForwarder(RootEventSource rootEventSource)
{
this.rootEventSource = rootEventSource;
}
public event Signal AnotherEvent
{
add { this.rootEventSource.RootEvent += value; }
remove { this.rootEventSource.RootEvent -= value; }
}
}

Updating a C# 2.0 events example to be idiomatic with C# 3.5?

I have a short events example from .NET 2.0 that I've been using as a reference point for a while. We're now upgrading to 3.5, though, and I'm not clear on the most idiomatic way to do things. How would this simple events example get updated to reflect idioms that are now available in .NET 3.5?
// Args class.
public class TickArgs : EventArgs {
private DateTime TimeNow;
public DateTime Time {
set { TimeNow = value; }
get { return this.TimeNow; }
}
}
// Producer class that generates events.
public class Metronome {
public event TickHandler Tick;
public delegate void TickHandler(Metronome m, TickArgs e);
public void Start() {
while (true) {
System.Threading.Thread.Sleep(3000);
if (Tick != null) {
TickArgs t = new TickArgs();
t.Time = DateTime.Now;
Tick(this, t);
}
}
}
}
// Consumer class that listens for events.
public class Listener {
public void Subscribe(Metronome m) {
m.Tick += new Metronome.TickHandler(HeardIt);
}
private void HeardIt(Metronome m, TickArgs e) {
System.Console.WriteLine("HEARD IT AT {0}",e.Time);
}
}
// Example.
public class Test {
static void Main() {
Metronome m = new Metronome();
Listener l = new Listener();
l.Subscribe(m);
m.Start();
}
}

// Args class.
public class TickArgs : EventArgs {
private DateTime TimeNow;
// Auto property used
public DateTime Time { get; set; }
}
// Producer class that generates events.
public class Metronome {
public event TickHandler Tick;
public delegate void TickHandler(Metronome m, TickArgs e);
public void Start() {
while (true) {
System.Threading.Thread.Sleep(3000);
// Thread safety introduced
TickHandler ticker = Tick;
if (ticker != null) {
// Object initialiser added
TickArgs t = new TickArgs {
Time = DateTime.Now;
}
ticker(this, t);
}
}
}
}
// Consumer class that listens for events.
public class Listener {
public void Subscribe(Metronome m) {
// Event handler replaced with llambda function
m.Tick += (mm, e) => System.Console.WriteLine("HEARD IT AT {0}",e.Time)
}
}
// Example.
public class Test {
static void Main() {
Metronome m = new Metronome();
Listener l = new Listener();
l.Subscribe(m);
m.Start();
}
}
You can improve the Tick event like this
// Producer class that generates events.
public class Metronome {
// Add a dummy event handler and ensure that there's no unsafe thread issues
public event TickHandler Tick = (m, e) => {};
public delegate void TickHandler(Metronome m, TickArgs e);
public void Start() {
while (true) {
System.Threading.Thread.Sleep(3000);
// no need to check for null before calling
Tick(this, new TickArgs { Time = DateTime.Now; });
}
}
}
I don't have a compile to hand but you can improve the Tick event like this I think
// Producer class that generates events.
public class Metronome {
// Add a dummy event handler and ensure that there's no unsafe thread issues
public event EventHandler<TickArgs> Tick = (m, e) => {};
public void Start() {
while (true) {
System.Threading.Thread.Sleep(3000);
// no need to check for null before calling
Tick(this, new TickArgs { Time = DateTime.Now; });
}
}
}

For a start, you shouldn't define your own delegate types for events. Instead, use System.EventHandler<T> or System.EventHandler.
Also, you can use auto-implemented properties for your TickArgs class (which, incidentally, should really be called TickEventArgs, in accord with .NET conventions):
public class TickEventArgs : EventArgs
{
public DateTime Time
{
get;
set;
}
}
As for the events themselves, there are some gotchas that you should know about in .NET which you can read about in some of John Skeet's multithreading articles:
http://www.yoda.arachsys.com/csharp/events.html
Note that events in .NET 4 work differently and a lot of the gotchas that exist in 3.5 have been cleaned up.

For starters you can use auto generated properties:
public class TickArgs : EventArgs {
public DateTime Time {
set;
get;
}
}
You also do not need to instantiate the listening delegate:
public void Subscribe(Metronome m) {
m.Tick += HeardIt;
}

Here's how I would do it. First, note that I've made TickArgs sealed and immutable via readonly on the member variables. Second, I removed the TickHandler delegate and replaced with an EventHandler<TickArgs>. Thirdly, the Tick event itself is now private (renamed to _Tick) and accessed via a property. Lastly, the hook into the event in Listener uses a lambda expression (i.e. inline delegate) rather than an explicit method.
namespace Events3
{
using System;
// Args class.
public sealed class TickArgs : EventArgs
{
private readonly DateTime TimeNow;
public DateTime Time
{
get { return this.TimeNow; }
}
public TickArgs(DateTime TimeNow)
{
this.TimeNow = TimeNow;
}
}
// Producer class that generates events.
public sealed class Metronome
{
private event EventHandler<TickArgs> _Tick;
public event EventHandler<TickArgs> Tick
{
add { this._Tick += value; }
remove { this._Tick -= value; }
}
public void Start()
{
while (true)
{
System.Threading.Thread.Sleep(3000);
EventHandler<TickArgs> tick = this._Tick;
if (tick != null)
{
tick(this, new TickArgs(DateTime.Now));
}
}
}
}
// Consumer class that listens for events.
public sealed class Listener
{
public void Subscribe(Metronome m)
{
m.Tick += (sender, e) =>
{
System.Console.WriteLine("HEARD IT AT {0}", e.Time);
};
}
}
// Example.
public static class Test
{
static void Main()
{
Metronome m = new Metronome();
Listener l = new Listener();
l.Subscribe(m);
m.Start();
}
}
}

Super-simple example of C# observer/observable with delegates

I recently started digging into C# but I can't by my life figure out how delegates work when implementing the observer/observable pattern in the language.
Could someone give me a super-simple example of how it is done? I have googled this, but all of the examples I found were either too problem-specific or too "bloated".

The observer pattern is usually implemented with events.
Here's an example:
using System;
class Observable
{
public event EventHandler SomethingHappened;
public void DoSomething() =>
SomethingHappened?.Invoke(this, EventArgs.Empty);
}
class Observer
{
public void HandleEvent(object sender, EventArgs args)
{
Console.WriteLine("Something happened to " + sender);
}
}
class Test
{
static void Main()
{
Observable observable = new Observable();
Observer observer = new Observer();
observable.SomethingHappened += observer.HandleEvent;
observable.DoSomething();
}
}
See the linked article for a lot more detail.
Note that the above example uses C# 6 null-conditional operator to implement DoSomething safely to handle cases where SomethingHappened has not been subscribed to, and is therefore null. If you're using an older version of C#, you'd need code like this:
public void DoSomething()
{
var handler = SomethingHappened;
if (handler != null)
{
handler(this, EventArgs.Empty);
}
}

In this model, you have publishers who will do some logic and publish an "event."
Publishers will then send out their event only to subscribers who have subscribed to receive the specific event.
In C#, any object can publish a set of events to which other applications can subscribe.
When the publishing class raises an event, all the subscribed applications are notified.
The following figure shows this mechanism.
Simplest Example possible on Events and Delegates in C#:
code is self explanatory, Also I've added the comments to clear out the code.
using System;
public class Publisher //main publisher class which will invoke methods of all subscriber classes
{
public delegate void TickHandler(Publisher m, EventArgs e); //declaring a delegate
public TickHandler Tick; //creating an object of delegate
public EventArgs e = null; //set 2nd paramter empty
public void Start() //starting point of thread
{
while (true)
{
System.Threading.Thread.Sleep(300);
if (Tick != null) //check if delegate object points to any listener classes method
{
Tick(this, e); //if it points i.e. not null then invoke that method!
}
}
}
}
public class Subscriber1 //1st subscriber class
{
public void Subscribe(Publisher m) //get the object of pubisher class
{
m.Tick += HeardIt; //attach listener class method to publisher class delegate object
}
private void HeardIt(Publisher m, EventArgs e) //subscriber class method
{
System.Console.WriteLine("Heard It by Listener");
}
}
public class Subscriber2 //2nd subscriber class
{
public void Subscribe2(Publisher m) //get the object of pubisher class
{
m.Tick += HeardIt; //attach listener class method to publisher class delegate object
}
private void HeardIt(Publisher m, EventArgs e) //subscriber class method
{
System.Console.WriteLine("Heard It by Listener2");
}
}
class Test
{
static void Main()
{
Publisher m = new Publisher(); //create an object of publisher class which will later be passed on subscriber classes
Subscriber1 l = new Subscriber1(); //create object of 1st subscriber class
Subscriber2 l2 = new Subscriber2(); //create object of 2nd subscriber class
l.Subscribe(m); //we pass object of publisher class to access delegate of publisher class
l2.Subscribe2(m); //we pass object of publisher class to access delegate of publisher class
m.Start(); //starting point of publisher class
}
}
Output:
Heard It by Listener
Heard It by Listener2
Heard It by Listener
Heard It by Listener2
Heard It by Listener
.
.
.
(infinite times)

Here's a simple example:
public class ObservableClass
{
private Int32 _Value;
public Int32 Value
{
get { return _Value; }
set
{
if (_Value != value)
{
_Value = value;
OnValueChanged();
}
}
}
public event EventHandler ValueChanged;
protected void OnValueChanged()
{
if (ValueChanged != null)
ValueChanged(this, EventArgs.Empty);
}
}
public class ObserverClass
{
public ObserverClass(ObservableClass observable)
{
observable.ValueChanged += TheValueChanged;
}
private void TheValueChanged(Object sender, EventArgs e)
{
Console.Out.WriteLine("Value changed to " +
((ObservableClass)sender).Value);
}
}
public class Program
{
public static void Main()
{
ObservableClass observable = new ObservableClass();
ObserverClass observer = new ObserverClass(observable);
observable.Value = 10;
}
}
Note:
This violates a rule in that I don't unhook the observer from the observable, this is perhaps good enough for this simple example, but make sure you don't keep observers hanging off of your events like that. A way to handle this would be to make ObserverClass IDisposable, and let the .Dispose method do the opposite of the code in the constructor
No error-checking performed, at least a null-check should be done in the constructor of the ObserverClass

I've tied together a couple of the great examples above (thank you as always to Mr. Skeet and Mr. Karlsen) to include a couple of different Observables and utilized an interface to keep track of them in the Observer and allowed the Observer to to "observe" any number of Observables via an internal list:
namespace ObservablePattern
{
using System;
using System.Collections.Generic;
internal static class Program
{
private static void Main()
{
var observable = new Observable();
var anotherObservable = new AnotherObservable();
using (IObserver observer = new Observer(observable))
{
observable.DoSomething();
observer.Add(anotherObservable);
anotherObservable.DoSomething();
}
Console.ReadLine();
}
}
internal interface IObservable
{
event EventHandler SomethingHappened;
}
internal sealed class Observable : IObservable
{
public event EventHandler SomethingHappened;
public void DoSomething()
{
var handler = this.SomethingHappened;
Console.WriteLine("About to do something.");
if (handler != null)
{
handler(this, EventArgs.Empty);
}
}
}
internal sealed class AnotherObservable : IObservable
{
public event EventHandler SomethingHappened;
public void DoSomething()
{
var handler = this.SomethingHappened;
Console.WriteLine("About to do something different.");
if (handler != null)
{
handler(this, EventArgs.Empty);
}
}
}
internal interface IObserver : IDisposable
{
void Add(IObservable observable);
void Remove(IObservable observable);
}
internal sealed class Observer : IObserver
{
private readonly Lazy<IList<IObservable>> observables =
new Lazy<IList<IObservable>>(() => new List<IObservable>());
public Observer()
{
}
public Observer(IObservable observable) : this()
{
this.Add(observable);
}
public void Add(IObservable observable)
{
if (observable == null)
{
return;
}
lock (this.observables)
{
this.observables.Value.Add(observable);
observable.SomethingHappened += HandleEvent;
}
}
public void Remove(IObservable observable)
{
if (observable == null)
{
return;
}
lock (this.observables)
{
observable.SomethingHappened -= HandleEvent;
this.observables.Value.Remove(observable);
}
}
public void Dispose()
{
for (var i = this.observables.Value.Count - 1; i >= 0; i--)
{
this.Remove(this.observables.Value[i]);
}
}
private static void HandleEvent(object sender, EventArgs args)
{
Console.WriteLine("Something happened to " + sender);
}
}
}

Applying the Observer Pattern with delegates and events in c# is named "Event Pattern" according to MSDN which is a slight variation.
In this Article you will find well structured examples of how to apply the pattern in c# both the classic way and using delegates and events.
Exploring the Observer Design Pattern
public class Stock
{
//declare a delegate for the event
public delegate void AskPriceChangedHandler(object sender,
AskPriceChangedEventArgs e);
//declare the event using the delegate
public event AskPriceChangedHandler AskPriceChanged;
//instance variable for ask price
object _askPrice;
//property for ask price
public object AskPrice
{
set
{
//set the instance variable
_askPrice = value;
//fire the event
OnAskPriceChanged();
}
}//AskPrice property
//method to fire event delegate with proper name
protected void OnAskPriceChanged()
{
AskPriceChanged(this, new AskPriceChangedEventArgs(_askPrice));
}//AskPriceChanged
}//Stock class
//specialized event class for the askpricechanged event
public class AskPriceChangedEventArgs : EventArgs
{
//instance variable to store the ask price
private object _askPrice;
//constructor that sets askprice
public AskPriceChangedEventArgs(object askPrice) { _askPrice = askPrice; }
//public property for the ask price
public object AskPrice { get { return _askPrice; } }
}//AskPriceChangedEventArgs

/**********************Simple Example ***********************/
class Program
{
static void Main(string[] args)
{
Parent p = new Parent();
}
}
////////////////////////////////////////////
public delegate void DelegateName(string data);
class Child
{
public event DelegateName delegateName;
public void call()
{
delegateName("Narottam");
}
}
///////////////////////////////////////////
class Parent
{
public Parent()
{
Child c = new Child();
c.delegateName += new DelegateName(print);
//or like this
//c.delegateName += print;
c.call();
}
public void print(string name)
{
Console.WriteLine("yes we got the name : " + name);
}
}

I did't want to change my source code to add additional observer , so I have written following simple example:
//EVENT DRIVEN OBSERVER PATTERN
public class Publisher
{
public Publisher()
{
var observable = new Observable();
observable.PublishData("Hello World!");
}
}
//Server will send data to this class's PublishData method
public class Observable
{
public event Receive OnReceive;
public void PublishData(string data)
{
//Add all the observer below
//1st observer
IObserver iObserver = new Observer1();
this.OnReceive += iObserver.ReceiveData;
//2nd observer
IObserver iObserver2 = new Observer2();
this.OnReceive += iObserver2.ReceiveData;
//publish data
var handler = OnReceive;
if (handler != null)
{
handler(data);
}
}
}
public interface IObserver
{
void ReceiveData(string data);
}
//Observer example
public class Observer1 : IObserver
{
public void ReceiveData(string data)
{
//sample observers does nothing with data :)
}
}
public class Observer2 : IObserver
{
public void ReceiveData(string data)
{
//sample observers does nothing with data :)
}
}

Something like this:
// interface implementation publisher
public delegate void eiSubjectEventHandler(eiSubject subject);
public interface eiSubject
{
event eiSubjectEventHandler OnUpdate;
void GenereteEventUpdate();
}
// class implementation publisher
class ecSubject : eiSubject
{
private event eiSubjectEventHandler _OnUpdate = null;
public event eiSubjectEventHandler OnUpdate
{
add
{
lock (this)
{
_OnUpdate -= value;
_OnUpdate += value;
}
}
remove { lock (this) { _OnUpdate -= value; } }
}
public void GenereteEventUpdate()
{
eiSubjectEventHandler handler = _OnUpdate;
if (handler != null)
{
handler(this);
}
}
}
// interface implementation subscriber
public interface eiObserver
{
void DoOnUpdate(eiSubject subject);
}
// class implementation subscriber
class ecObserver : eiObserver
{
public virtual void DoOnUpdate(eiSubject subject)
{
}
}
.
observer pattern C# with event
.
link to the repository