Args

name	Remarks
CancelRoutedEventArgs
FunctionEventArgs!1
KeyboardHookEventArgs
MouseHookEventArgs

You can use FunctionEventArgs!1 to create a custom event args

step 1: create a EventHandler

public event EventHandler<FunctionEventArgs<myArgument>> myEventChanged;

public class myArgument
{
    public string OldValue { get; internal set; }
    public string NewValue { get; internal set; }
}

step2: Notify change where necessary

myEventChanged?.Invoke(this, new FunctionEventArgs<myArgument>(OldValue = "Old", NewValue = "New"));