We Keep Coding

Why does basic EventArgs class exist

this is more theoretical question. I know that every event in C# has to have 2 parameters: object and eventargs. It's clear. But why does the basic eventargs class even exist when it's impossible to pass any data with it? Of course I can make new EventArgs class that inherits from the basic one, but I just miss the point of the class that can't carry any data.

This is about future-proofing your code.
The theory goes that if at some point you discover that your code should publish more data to event handlers than it did before, you can easily just add more properties to the object you pass to those event handlers.
If, for some reason, the class that holds those data is not under your control you inherit from it, and add your properties to the inherited class. So far so good.
But, if you never passed any object to the event handler in the first place, you cannot add a new parameter to the event delegate without existing code breaking.
As such, that you pass what amounts to a dummy object, EventArgs.Empty to events now give you the ability to later on inherit from EventArgs and start passing data to the same events, without having to change the event handlers at all. I most cases, you don't even have to recompile assemblies that uses the event handler.
So EventArgs is just a handy class you pass to event handlers, you could just as easily create your own, but since it has no meaning except to be a placeholder for possible future changes, there's no need to create your own, simply use EventArgs.

C# - issue with custom raising events

I have my class where I define my event:
public class EventRaiserUtility
{
public event EventHandler updateList;
public void updateListEvent()
{
if (updateList != null)
{
updateList(this, EventArgs.Empty);
}
}
public static EventRaiserUtility raiser = new EventRaiserUtility();
}
and this is where I raise my event:
EventRaiserUtility.raiser.updateListEvent();
and finally this is where I'm trying to create the listener:
...
EventRaiserUtility.raiser.updateList += new EventHandler(raiser_updateList);
//placed in the init method of another class
...
private void raiser_updateList(object sender, EventArgs e)
{
connType = MainWindowViewModel.getTTC();
}
Simply: this event has to notify when a list is updated and then update another list, with getTTC() with raiser_updateList.
But raiser_updateList is never called. Why? All my 3 snippets of code are in 3 different classes (same project), but this isn't a problem... right?

You're creating a new EventRaiserUtility just before you call updateListEvent (which should have a capital U to follow .NET conventions, by the way; ditto updateList => UpdateList) - but you're creating a separate EventRaiserUtility in order to subscribe to the event. They're different objects, so have different event subscribers. If you always create a new object before raising the event, there could never be any subscribers.
You should have a single EventRaiserUtility stored in an instance variable in the containing class - you'd create that on construction, then subscribe to the event in one place an raise it in another... but because they'd be talking about the same EventRaiserUtility object, you wouldn't lose the subscription.
(It's not clear that this utility class actually has much value, to be honest - why aren't you just declaring the event in your class directly? And why declare your own delegate when EventHandler has exactly the same signature?)

As far as I can see - you are subscribing to the event of one instance of EventRaiserUtility, but raising event from another instance which has no subscribers

you need one object to really own the event. Maybe that is the EventRaiserUtility, but you'd still need to make the same instance available in both classes. Without knowing the relationship between those classes

Why public event cannot be invoked outside directly?

Consider we have a class with event declared:
public class FooBar
{
public event EventHandler FooBarEvent;
}
Despite of "publicness" of the event, we cannot call FooBarEvent.Invoke from outside.
This is overcame by modyfing a class with the following approach:
public class FooBar
{
public event EventHandler FooBarEvent;
public void RaiseFooBarEvent(object sender, EventArgs eventArguments)
{
FooBarEvent.Invoke(sender, eventArguments);
}
}
Why accessing public events outside is limited by adding and removing listeners only?

Defining a public event merely gives consumers the ability to subscribe and unsubscribe from it. The ability to raise the event is limited to the type hierarchy which declares the event.
Allowing all subscribers to also be able to raise the event would be a bit chaotic. Imagine for example I had a TextBox class which had a Focused event. If any old consumer could raise the event then the Focused event could easily fire when the TextBox class wasn't actually focused. This would make it nearly impossible to maintain any type of invariant during an event.

Personally I think this is done to properly convey the design principles behind the whole events architecture.
The purpose of an event is to notify a listener of said event occurring in a given object.
What's the point of raising events of classes that don't belong to you?

That's what events are for. If you want to invoke it publicly you probably need delegates not events
Events gives encapsulation,
It prevents other classes from assigning anything to it
It prevents passing it as a parameter to methods
It prevents assigning it to any variable
It prevents calling it from another classes (not even derived classes have access to it)
etc
public accessibility tells that it can be subscribed from anywhere, not invoked from anywhere.

the answer to your question is
An event in C# is a way for a class to provide notifications to clients of that class when some interesting thing happens to an object.
Invoking the event from outside doesn't makes sense therefore it is not allowed.

I think you should change your perspective on how events work. Other classes shouldn't "own" the event and trigger it. Classes which "listen" to the event by "subscribing" to it and do a certain action when this event occurs.

That's the way the language is defined - an event can only be fired by the owning class. If you must fire it from a different class, have the owning class define a public method that will fire the event:
public FireFooBarEvent (object sender, EventArgs args)
{
if(FooBarEvent != null)
FooBarEvent(sender, args);
}
And call this method from any class.

Mixing enums with event classes in an event aggregator

I attempted to implement my own simple event aggregator recently. I got a lot of inspiration from the event aggregator article on MSDN. There is one thing that I notice about the event aggregator on MSDN is the events are actually classes on their own. This isn't really a bad thing at all. However, I just find it awkward to always create a new empty class for every single little event.
The reason I find it awkward is because of the need to create a class for every single granular event. A mouse click event, for instance, would have double_click, single_click, left_click, right_click, etc. And all of these are going to have a class of its own. It gets messy after a while.
So in my own implementation, I thought I could make it in such a way where the ClickEvent is a class, but all the granular events related to the Click event would then be "types" of the ClickEvent. In this case, the "types" are enum. The usage would look something like this:
//Publisher
eventAggregator.GetEvent<ClickEvent>.Publish(ClickEventType.Double_Click, eventArgs);
//Subscriber
eventAggregator.GetEvent<ClickEvent>.Subscribe(ClickEventType.Double_Click, handlerMethod);
However, I'm not sure if this implementation defeats the whole purpose of having a strongly typed event? Now, it seems like the ClickEvent is merely a container for the different event enum types.

Yes it does (seem like a container that is) - your handler will fire regardless of the click type and there will be some code required in the handler to determine the type of click, which makes things a little messier.
If your issue is mostly the organisation of the files/classes and keeping the code tidy, why not just create the click events as nested classes within a main click class
e.g.
public static class ClickEvents // Prevent instantiation
{
public class SingleLeft { }
public class SingleRight { }
public class DoubleLeft { }
public class DoubleRight { }
// Are there any more click events possible?!
}
eventAggregator.GetEvent<ClickEvents.SingleLeft>.Publish();
Aside from that, it's the uniqueness of the type that determines the event signature, and therefore multiple types are required to satisfy this particular implementation
At least the above keeps your handler code clean
void HandleLeftClick()
{
}
vs
void HandleClick(ClickArgs e)
{
if(e.ClickType == ClickType.Left)
{
}
}
Edit:
Also remember that you can subscribe multiple events to the same handler if you want to handle more than one click type:
eventAggregator.GetEvent<ClickEvents.SingleLeft>.Subscribe(HandlerMethod);
eventAggregator.GetEvent<ClickEvents.SingleRight>.Subscribe(HandlerMethod);
(this would work in the rare situation that the subscriber didn't care which mouse button was clicked)

I think you missed one possibility. You see, you don't have to create a new class for each notification. Instead, you are free to reuse classes but carry some additional state of arbitrary complexity inside.
public class MouseClickNotification {
public bool IsDoubleClick;
public MouseButton ClickedButton;
// any additional stuff
This way it is you who precisely define the granularity of your notification model.

Why to use events somewhere where method is enough?

I read some events tutorial and just do not get what is the benefit in simple code like this..method should be used the same way:
class Bulb
{ public delegate void handler();
public event handler Glowing;
...
Glowing+=SomeMethod;
private void TurnOn
{
Glowing();
}
private void SomeMethod
{
}
}

Simply Events allow others using your code to perform some custom Implementation they want when that Event occurs (when Bulb is Glowing).
Simply calling your method won't tell anybody that something has happened.
Events are very basic Element of any Event Driven Programming
If your program doesn't need to tell about an event you don't need to implement such Functionality. However having such functionality has benefits.
For Example when using a List Class you dont know when an Item got added to it (if at some point some other code does that) but in a ObservableCollection you get notifications when Items are Added or Removed.
An event is a message sent by an object to signal the occurrence of an action. The action could be caused by user interaction, such as a mouse click, or it could be triggered by some other program logic.

The idea is that a different class which can hold Three different Bulbs can get notified by the event (if it implements a handler) that the light has been turned on and is Glowing.
So the benefit does not reside in the simply class but in what ever classes/objects are going to be holding/using instances of the Bulb class.
Hope that made some sense :)

Events over methods become handy when you have a class dependency that needs to know or be notified about a stateful change:
public class Lamp
{
Bulb inThelamp = new Bulb();
inTheLamp.Glowing += myLampMethod;
// If these arguments have been defined for this event that is
public void myLampMethod(object sender, EventArgs e)
{
// Code to react to the light suddenly being on
}
}
This allows the Lamp class to recognize that something has turned the bulb on. In many cases it will be through some action in the Lamp (click, pushknob, etc). But in some cases it could be an external class that calls a public Bulb property directly without using the Lamp itself (such is if(PowerCompany.BillsPaid) Lamp.BulbInTheLamp.TurnedOn();). This is all assuming that the modifiers are set to allow this kind of access.
The point is that it allows notification of an occurrence rather than requiring that a particular method be called manually each time you want an action to occur.