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How to make an event which gets triggered in another class

In my code for the PluginManager the event PluginEvent gets triggered after
a plugin has been added. But I want to get the event also triggered in the test class.
Somehow I cant solve this problem. The event only gets triggered in the PluginManager class. I read some articles how to create events and so on, but I got even more confused
PluginManager class
public class PluginEventArgs
{
public PluginEventArgs(string s) { Text = s; }
public String Text { get; private set; } // readonly
}
public class PluginManager
{
// Declare the delegate (if using non-generic pattern).
public delegate void PluginEventHandler(object sender, PluginEventArgs e);
// Declare the event.
public event PluginEventHandler PluginEvent;
protected virtual void RaiseSampleEvent(string message)
{
if (PluginEvent != null)
PluginEvent(this, new PluginEventArgs(message));
}
public PluginManager()
{
PluginEvent += PluginManager_PluginEvent;
SomeMethod();
}
void PluginManager_PluginEvent(object sender, PluginEventArgs e)
{
//This event gets triggered =)
}
public void SomeMethod()
{
//Code
RaiseSampleEvent("Name of the Plugin");
//Code
}
}
My test class:
class test
{
public test()
{
PluginManager pluginMg = new PluginManager();
pluginMg.PluginEvent += pluginMg_PluginEvent;
}
//I want this event to get triggered when a new plugin has been found
void pluginMg_PluginEvent(object sender, PluginEventArgs e)
{
MessageBox.Show(e.Text);
}
}
How can I manage to get the event triggered in the test class?
Thanks for any advise!

You're actually doing things right except for one logical Mistake.
In your test class you're creating the PluginManager by using the constructor. The constructor of PluginManager first subscribes to the event and then raises it.
AFTERWARDS you're subscribing to that event.
The simple Problem is that when you are raising the event your test class has not subscribed yet. When you raise that event again everything should work out just fine.
Another thing is that I would use the generic EventHandler class instead of creating your own delegates. This keeps your code cleaner and everyone knows that this is meant to be an event at first glance.
Just inherit PlugInEventArgs from EventArgs and then use EventHandler.

In your PluginManager class you shouldn't subscribe to your own event PluginEvent, you should subscribe to an external event or just raise the PluginEvent.
Let me give you an example:
public class PluginEventArgs
{
public PluginEventArgs(string s) { Text = s; }
public String Text { get; private set; } // readonly
}
public class OtherClass
{
public event PluginEventHandler PluginEvent;
private void RaiseEvent()
{
if (null != PluginEvent)
PluginEvent(this, new PluginEventArgs("some message"));
}
}
public delegate void PluginEventHandler(object sender, PluginEventArgs e);
public class PluginManager
{
public event PluginEventHandler PluginEvent;
private OtherClass otherClass;
protected virtual void RaiseSampleEvent(string message)
{
if (PluginEvent != null)
PluginEvent(this, new PluginEventArgs(message));
}
public PluginManager(OtherClass otherClass)
{
this.otherClass = otherClass;
this.otherClass.PluginEvent += otherClass_PluginEvent;
SomeMethod();
}
void otherClass_PluginEvent(object sender, PluginEventArgs e)
{
if (PluginEvent != null)
PluginEvent(sender, e); // this way the original sender and args are transferred.
}
public void SomeMethod()
{
//Code
RaiseSampleEvent("Name of the Plugin");
//Code
}
}
class test
{
public test()
{
OtherClass otherClass = new OtherClass();
PluginManager pluginMg = new PluginManager(otherClass);
pluginMg.PluginEvent += pluginMg_PluginEvent;
}
//I want this event to get triggered when a new plugin has been found
void pluginMg_PluginEvent(object sender, PluginEventArgs e)
{
MessageBox.Show(e.Text);
}
}

simple event c#

I have two classes, and i have to make an event to communicate between these classes.
Class a
{
public delegate void delegat(int a);
public event delegat exit;
...
private void a_FormClosed(object sender, FormClosedEventArgs e)
{
// My event named exit should run here, but I get exception!
exit(100);
}
}
Class b
{
a instance=new a();
a.exit+=new a.delegat(my_fun);
...
private void my_fun(int x)
{
if(x==100)
do_smth;
...
}
}
But the thing is that i get exception: "object reference not set to an instance of an object".
I can't understand what Am I doing wrong? Where should I make a new instance of this?
Thanks for help!

You are trying to assign the exit event on the class itself and not the instance e.g.
a.exit += ...
Should be:
instance.exit += ...
You also aren't checking whether your exit event has been assigned before attempting to fire it. There are other issues which you haven't taken into consideration like race conditions.
Here is a general example of a relatively safe way of handling events e.g.
public class A
{
public delegate void ExitHandler(object sender, int a);
public event ExitHandler Exit;
...
private void a_FormClosed(object sender, FormClosedEventArgs e)
{
OnExit(100);
}
protected virtual void OnExit(int a)
{
// take a reference to the event (incase it changes)
var handler = Exit;
if (handler != null)
{
handler(this, a);
}
}
}
public class B
{
private A _a;
public B()
{
_a = new A();
_a.Exit += (sender, value) => my_fun(value);
}
private void my_fun(int x)
{
if(x==100)
do_smth;
...
}
}

I would change "class a" code for calling the event to as follows:
Class a
{
public delegate void delegat(int a);
public event delegat exit;
...
private void a_FormClosed(object sender, FormClosedEventArgs e)
{
if (this.exit != null) // just in case a_FormClosed fires before assigning the event
exit(100);//here should run my event named exit but i get exception!
}
}

Verify if there is any subscriber exist to your event before raising it:
if (exit != null)
exit(100);
Another option - subscribing dummy event handler when you are defining event in class A:
public event delegat exit = (_) => { };
Also use PascalCase naming for types, events and methods. And there is predefined delegate in .NET which receives one argument and returns void: Action<T>

Try this
namespace foo
{
public delegate void delegat(int a);
Class a
{
public event delegat exit;
private void a_FormClosed(object sender, FormClosedEventArgs e)
{
if(exit != null)
{
exit(100);//here should run my event named exit but i get exception!
}
}
}
}
Class b
{
a instance=new a();
instance.exit+=new delegat(my_fun);
...
priavte void my_fun(int x)
{
if(x==100)
do_smth;
...
}
}

Notify when event from another class is triggered [duplicate]

This question already has answers here:
How to raise an event on Property Change?
(2 answers)
Closed 7 years ago.
I have
class A
{
B b;
//call this Method when b.Button_click or b.someMethod is launched
private void MyMethod()
{
}
??
}
Class B
{
//here i.e. a button is pressed and in Class A
//i want to call also MyMethod() in Class A after the button is pressed
private void Button_Click(object o, EventArgs s)
{
SomeMethod();
}
public void SomeMethod()
{
}
??
}
Class A has a instance of Class B.
How can this be done?

You'll need to declare a public event on class 'B' - and have class 'A' subscribe to it:
Something like this:
class B
{
//A public event for listeners to subscribe to
public event EventHandler SomethingHappened;
private void Button_Click(object o, EventArgs s)
{
//Fire the event - notifying all subscribers
if(SomethingHappened != null)
SomethingHappened(this, null);
}
....
class A
{
//Where B is used - subscribe to it's public event
public A()
{
B objectToSubscribeTo = new B();
objectToSubscribeTo.SomethingHappened += HandleSomethingHappening;
}
public void HandleSomethingHappening(object sender, EventArgs e)
{
//Do something here
}
....

You need three things (which is marked by comments in code):
Declare event in class B
Raise event in class B when something happened (in your case - Button_Click event handler executed). Keep in mind that you need to verify if there are any subscribers exists. Otherwise you will get NullReferenceException on raising event.
Subscribe to event of class B. You need to have instance of class B, which even you want to subscribe (another option - static events, but those events will be raised by all instances of class B).
Code:
class A
{
B b;
public A(B b)
{
this.b = b;
// subscribe to event
b.SomethingHappened += MyMethod;
}
private void MyMethod() { }
}
class B
{
// declare event
public event Action SomethingHappened;
private void Button_Click(object o, EventArgs s)
{
// raise event
if (SomethingHappened != null)
SomethingHappened();
SomeMethod();
}
public void SomeMethod() { }
}

Have a look at rasing an event from Class B
Have a look at
Raising an Event
Handling and Raising Events
How to: Raise and Consume Events

How to pass an event to a method?

I would like to create a method that takes an event as an argument and adds eventHandler to it to handle it properly. Like this:
I have two events:
public event EventHandler Click;
public event EventHandler Click2;
Now I would like to pass a particular event to my method like this (pseudocode):
public AttachToHandleEvent(EventHandler MyEvent)
{
MyEvent += Item_Click;
}
private void Item_Click(object sender, EventArgs e)
{
MessageBox.Show("lalala");
}
ToolStripMenuItem tool = new ToolStripMenuItem();
AttachToHandleEvent(tool.Click);
Is it possible?
I've noticed that this code worked fine, and returned to my project and noticed that when I pass an event declared in my class, it works, but when I pass event from other class it still does not work.
What I get is this error:
The event
'System.Windows.Forms.ToolStripItem.Click'
can only appear on the left hand side
of += or -=

My original answer was suitable from within the class that defined the event, but you've since updated your question to reflect that you wish to accomplish this from outside the defining class, so I've stricken that.
Only the class that defines an event can refer to the implicit delegate variable that the event uses. From outside that class, you only have access to the add and remove methods, via += and -=. This means that you can't do what you're asking, directly. You can, however, use a functional approach.
class A{
public event EventHandler Event1;
public void TriggerEvent1(){
if(Event1 != null)
Event1(this, EventArgs.Empty);
}
}
class B{
static void HandleEvent(object o, EventArgs e){
Console.WriteLine("Woo-hoo!");
}
static void AttachToEvent(Action<EventHandler> attach){
attach(HandleEvent);
}
static void Main(){
A a = new A();
AttachToEvent(handler=>a.Event1 += handler);
a.TriggerEvent1();
}
}

I did it like this:
public AttachToHandleEvent(Object obj, string EventName)
{
EventInfo mfi = obj.GetType().GetEvent(EventName);
MethodInfo mobj = mfi.GetAddMethod();
mobj.Invoke(obj, new object[] { Item_Click});
}
private void Item_Click(object sender, EventArgs e)
{
MessageBox.Show("lalala");
}
ToolStripMenuItem tool = new ToolStripMenuItem();
AttachToHandleEvent(tool "Click");
Thank you all for advice. This solution could not be done without your help.

It's not possible. You can use a delegate instead of an event if that meets your needs.

Just write tool.Click += Item_Click;
Edit: From MSDN "Events can only be invoked from within the class or struct where they (it) are declared". So what you are trying to do is not possible. Could you elaborate more on your needs? Why would you want to pass an event as a parameter?

delegate void doIt(object sender, object data);
event doIt OnDoIt;
void add(doIt theDel)
{
OnDoIt += theDel;
}
void doIt1(object a, object b)
{
}
void doIt2(object a, object b)
{
}
void add()
{
add(doIt1);
add(doIt2);
}

Your question suggests that you got some mechanisms wrong:
You can't pass events!
You most probably want to pass a function as a parameter, so the calling method will call that other method at some point. In technical terms this is a delegate. I suggest using the already defined Action class. Here's an example snippet:
void MyFunction (string otherArguments, Action onFinished){
...
if (onFinished != null)
onFinished.Invoke();
}
The nice thing about this is that when calling MyFunction you can declare the Action using the inline syntax:
MyFunction("my other argument", ()=>{
///do stuff here, which will be execuded when the action is invoked
});

I pass functions/methods (instead of events) like this:
class A
{
public void something()
{
var myAction =
new Action<object, object>((sender, evArgs) => {
MessageBox.Show("hiii, event happens " + (evArgs as as System.Timers.ElapsedEventArgs).SignalTime);
});
B.timer(myAction);
}
}
class B
{
public static void timer( Action<object, System.Timers.ElapsedEventArgs> anyMethod)
{
System.Timers.Timer myTimer = new System.Timers.Timer();
myTimer.Elapsed += new System.Timers.ElapsedEventHandler(anyMethod);
myTimer.Interval = 2000;
myTimer.Start();
}
}

Giving an update to this question with an object oriented solution.
Instead of using an Action<EventHandler> that registers the event, you could create an object handling that for you
public class AEvent
{
private readonly A aInstance;
private AEvent(A instance) {
aInstance = instance;
}
public void Add(EventHandler eventHandler)
=> a.Event1 += eventHandler;
public void Remove(EventHandler eventHandler)
=> a.Event1 -= eventHandler;
public EventHandler Invoke => aInstance.Event1;
}
Then later on use that object like this:
static void Main(){
A a = new A();
AEvent aEvent = new AEvent(A)
aEvent.Add(handler);
a.Invoke();
}

One approach I haven't seen here would be to create an object which has delegates for subscribe and unsubscribe. Here is a complete example program.
class Program
{
private event EventHandler<EventArgs> eventHandler;
public static void Main(string[] args)
{
Program program = new Program();
Thing thing = new Thing(new EventWrapper<EventArgs>(
delegate(EventHandler<EventArgs> handler) { program.eventHandler += handler; },
delegate(EventHandler<EventArgs> handler) { program.eventHandler -= handler; }
));
// events are fired
program.eventHandler?.Invoke(program, EventArgs.Empty);
thing.Unsubscribe();
}
}
class Thing
{
private readonly Action<EventHandler<EventArgs>> _unsubscribeEventHandler;
public Thing(EventWrapper<EventArgs> eventHandler)
{
this._unsubscribeEventHandler = eventHandler.Unsubscribe;
eventHandler.Subscribe?.Invoke(OnEvent);
Console.WriteLine("subscribed");
}
private void OnEvent(object? sender, EventArgs e)
{
Console.WriteLine("event fired");
}
public void Unsubscribe()
{
_unsubscribeEventHandler?.Invoke(OnEvent);
Console.WriteLine("unsubscribed");
}
}
class EventWrapper<T> where T : EventArgs
{
public Action<EventHandler<T>> Subscribe { get; private set; }
public Action<EventHandler<T>> Unsubscribe { get; private set; }
public EventWrapper(Action<EventHandler<T>> subscribe, Action<EventHandler<T>> unsubscribe)
{
Subscribe = subscribe;
Unsubscribe = unsubscribe;
}
}
In this example, we created a new class called EventWrapper<T> which wraps delegates for += and -= and exposes them with Subscribe and Unsubscribe methods. The delegates will need to be created by the class which created the event.

How to dispatch events in C#

I wish to create own events and dispatch them.
I never done this before in C#, only in Flex.. I guess there must be a lot of differencies.
Can anyone provide me a good example?

There is a pattern that is used in all library classes. It is recommended for your own classes too, especially for framework/library code. But nobody will stop you when you deviate or skip a few steps.
Here is a schematic based on the simplest event-delegate, System.Eventhandler.
// The delegate type. This one is already defined in the library, in the System namespace
// the `void (object, EventArgs)` signature is also the recommended pattern
public delegate void Eventhandler(object sender, Eventargs args);
// your publishing class
class Foo
{
public event EventHandler Changed; // the Event
protected virtual void OnChanged() // the Trigger method, called to raise the event
{
// make a copy to be more thread-safe
EventHandler handler = Changed;
if (handler != null)
{
// invoke the subscribed event-handler(s)
handler(this, EventArgs.Empty);
}
}
// an example of raising the event
void SomeMethod()
{
if (...) // on some condition
OnChanged(); // raise the event
}
}
And how to use it:
// your subscribing class
class Bar
{
public Bar()
{
Foo f = new Foo();
f.Changed += Foo_Changed; // Subscribe, using the short notation
}
// the handler must conform to the signature
void Foo_Changed(object sender, EventArgs args) // the Handler (reacts)
{
// the things Bar has to do when Foo changes
}
}
And when you have information to pass along:
class MyEventArgs : EventArgs // guideline: derive from EventArgs
{
public string Info { get; set; }
}
class Foo
{
public event EventHandler<MyEventArgs> Changed; // the Event
...
protected virtual void OnChanged(string info) // the Trigger
{
EventHandler handler = Changed; // make a copy to be more thread-safe
if (handler != null)
{
var args = new MyEventArgs(){Info = info}; // this part will vary
handler(this, args);
}
}
}
class Bar
{
void Foo_Changed(object sender, MyEventArgs args) // the Handler
{
string s = args.Info;
...
}
}
Update
Starting with C# 6 the calling code in the 'Trigger' method has become a lot easier, the null test can be shortened with the null-conditional operator ?. without making a copy while keeping thread-safety:
protected virtual void OnChanged(string info) // the Trigger
{
var args = new MyEventArgs{Info = info}; // this part will vary
Changed?.Invoke(this, args);
}

Events in C# use delegates.
public static event EventHandler<EventArgs> myEvent;
static void Main()
{
//add method to be called
myEvent += Handler;
//call all methods that have been added to the event
myEvent(this, EventArgs.Empty);
}
static void Handler(object sender, EventArgs args)
{
Console.WriteLine("Event Handled!");
}

Using the typical .NET event pattern, and assuming you don't need any special arguments in your event. Your typical event and dispatch pattern looks like this.
public class MyClassWithEvents
{
public event EventHandler MyEvent;
protected void OnMyEvent(object sender, EventArgs eventArgs)
{
if (MyEvent != null)
{
MyEvent(sender, eventArgs);
}
}
public void TriggerMyEvent()
{
OnMyEvent(sender, eventArgs);
}
}
Tying something into the event can be as simple as:
public class Program
{
public static void Main(string[] args)
{
MyClassWithEvents obj = new MyClassWithEvents();
obj.MyEvent += obj_myEvent;
}
private static void obj_myEvent(object sender, EventArgs e)
{
//Code called when my event is dispatched.
}
}
Take a look at the links on this MSDN page

Look into 'delegates'.
Define a delegate
Use the delegate type as field/property (adding the 'Event' keyword)
You are now exposing events that users can hook into with "+= MyEventMethod;"
Hope this helps,