In ABL, you can define class events in a user-defined class or interface definition using the
DEFINE EVENT statement. This statement defines all of the event options described in this section, including the signature for its event handlers.
In .NET, Common Language Specification (CLS)-compliant languages, such as C# or Visual Basic, have their own syntax to define events in a .NET class or interface. Similar to any other .NET class member, when you look up information about a .NET event in the .NET class library documentation, it typically describes the event member using syntax from one or more of these .NET languages. For example, C# provides the event keyword to declare an event in a class definition. In this way, the language-specific syntax for .NET events defines event options that are similar to the ABL DEFINE EVENT statement.
For ABL class events, you define the strongly-typed handler signature in the DEFINE EVENT statement. For .NET events, the handler signature is specified using a .NET class type known as a delegate that is referenced in the event definition. Thus, using the same delegate type, .NET objects can conveniently define multiple events whose handlers use the same signature. For an ABL class event, you can define either an ABL method signature or you can reference a .NET delegate type to define a .NET signature for the event. Referencing a .NET delegate also allows you to implement a .NET interface event or an inherited .NET abstract event in an ABL class.
You can define any valid ABL method signature for an ABL class event. However, the mechanics of event handler execution might limit your choices in practice. Also, ABL requires any .NET delegate that you use to conform to .NET conventions for event handlers.
