Does .NET have a built-in EventArgs?

Question

I am getting ready to create a generic EventArgs class for event args that carry a single argument:

public class EventArg : EventArgs
{
    // Prope         


        

Answer 1

THERE IS NO BUILT-IN GENERIC ARGS. If you follow Microsoft EventHandler pattern, then you implement your derived EventArgs like you suggested: public class MyStringChangedEventArgs : EventArgs { public string OldValue { get; set; } }.

HOWEVER - if your team style guide accepts a simplification - your project can use a lightweight events, like this:

public event Action MyStringChanged;

usage :

// How to rise
private void OnMyStringChanged(string e)
{
    Action handler = MyStringChanged;    // thread safeness
    if (handler != null)
    {
        handler(this, e);
    }
}

// How to handle
myObject.MyStringChanged += (sender, e) => Console.WriteLine(e);

Usually a PoC projects use the latter approach. In professional applicatons, however, be aware of FX cop justification #CA1009: https://msdn.microsoft.com/en-us/library/ms182133.aspx