You must define any ABL class-based method or internal procedure that you want to subscribe as a handler for .NET events using a signature that is required by the .NET event. In .NET, this signature is defined by a delegate type that is associated with each event definition.

As a .NET convention, .NET event handler signatures have a void return type and consist of two input parameters, both of which are object references. The first parameter, identified as the sender, is always a reference to a System.Object instance, which represents the object that defines and publishes the event. The second parameter is typically a reference to an event arguments class instance that is generated by .NET each time it publishes the event. An event arguments class can be a System.EventArgs (the base class for all event arguments classes) or any derived class.

Note: .NET actually supports any signature for an event that is defined by its delegate. However, ABL only supports .NET event signatures defined by delegates that conform to this .NET convention.

The difference between one .NET delegate and another is the specific event arguments class specified for the event handler signature that it defines. Thus, .NET events that are defined with the same signature are typically defined with reference to the same delegate.