C# 5.0 Unleashed

EventHandler<T>

Requiring (or strongly advising, for the sake of consistency) developers to create their own EventArgs derived type is enough of a burden for them, but in the early days of .NET even that wasn’t enough. One had to create a custom EventHandler delegate with the typical sender plus event arguments signature:

public delegate void TickEventHandler(object sender, TickEventArgs e)

Since the advent of .NET 2.0, with the introduction of generics, this was simplified a bit through the introduction of EventHandler<T>:

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public delegate void EventHandler<TEventArgs>(object sender, TEventArgs e)    where TEventArgs : EventArgs

The generic constraint on the TEventArgs type argument has been removed in .NET Framework ...