rspec/rules/S4220/rule.adoc

When raising an event, two arguments are expected by the ``++EventHandler++`` delegate: Sender and event-data. There are three guidelines regarding these parameters:

* Do not pass ``++null++`` as the sender when raising a non-static event.
* Do pass ``++null++`` as the sender when raising a static event.
* Do not pass ``++null++`` as the event-data. If no data should be passed, then ``++EventArgs.Empty++`` should be used.

This rule raises an issue when any of these guidelines is not met.


== Noncompliant Code Example

----
using System;

namespace MyLibrary
{
  class Foo
  {
    public event EventHandler ThresholdReached;

    protected virtual void OnThresholdReached(EventArgs e)
    {
        ThresholdReached?.Invoke(null, e); // Noncompliant
    }
  }
}
----


== Compliant Solution

----
using System;

namespace MyLibrary
{
  class Foo
  {
    public event EventHandler ThresholdReached;

    protected virtual void OnThresholdReached(EventArgs e)
    {
        ThresholdReached?.Invoke(this, e);
    }
  }
}
----