Why public event cannot be invoked outside directly?

Question

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?

Answer 1

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.

Answer 2

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?