How Can I Properly Raise Inherited Events in C#?

Raising Inherited Events in C#

When working with inheritance in C#, it's important to understand how to properly access and raise events that are declared in a base class.

Suppose you have a base class with the following events defined:

public event EventHandler Loading;
public event EventHandler Finished;

In a class that inherits from this base class, you may encounter an error when attempting to raise these events directly, such as:

this.Loading(this, new EventHandler()); // Error: The event 'BaseClass.Loading' can only appear on the left hand side of += or -= 

This error occurs because events are not accessible like ordinary inherited members. To raise events from an inherited class, the following approach should be used:

1. In the base class, create protected methods that can be used to raise the events. These methods should be named using the prefix "On" followed by the event name:

protected virtual void OnLoading(EventArgs e)
{
    EventHandler handler = Loading;
    if(handler != null)
    {
        handler(this, e);
    }
}

protected virtual void OnFinished(EventArgs e)
{
    EventHandler handler = Finished;
    if(handler != null)
    {
        handler(this, e);
    }
}

2. In classes that inherit from this base class, the OnLoading and OnFinished methods can be called to raise the events:

public class InheritedClass : BaseClass
{
    public void DoSomeStuff()
    {
        ...
        OnLoading(EventArgs.Empty);
        ...
        OnFinished(EventArgs.Empty);
    }
}

By using protected methods to raise events in a base class, you can ensure that event handlers are properly invoked from derived classes while maintaining the encapsulation of the event-raising mechanism.

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