Event invocation

Context: Only the class that declares the event can invoke it (raise the event). Invocation is done by calling the delegate field (with null check).

Standard invocation pattern

public class Button
{
    public event EventHandler Clicked;

    protected virtual void OnClicked()
    {
        Clicked?.Invoke(this, EventArgs.Empty);
    }

    public void SimulateClick()
    {
        OnClicked();
    }
}

Why protected virtual?

Derived classes can override the raising method to add custom behavior.

public class SpecialButton : Button
{
    protected override void OnClicked()
    {
        Console.WriteLine("Special logging");
        base.OnClicked();
    }
}

Thread safety

Use a copy of the delegate to avoid null reference in multi‑threaded scenarios.

var handler = Clicked;
if (handler != null) handler(this, EventArgs.Empty);

Real-world usage example

Custom event raising: In a Timer class, you raise the Elapsed event when time is up using OnElapsed().

Example: System.Timers.Timer raises the Elapsed event on a background thread.

Related sections

• 7.2 Events
• 7.2.4 Standard pattern EventHandler and EventArgs