5.3.1.8 Event Handler Declarations

This section corresponds to MS-VBAL §5.3.1.8 Event Handler Declarations.

Static Semantics

A procedure of a class module handles an event when its name is VariableName_EventName: VariableName is a WithEvents variable of the same class module (RD-VBAL §5.2.3.1.2) and EventName an event of the class that is the variable's declared type (RD-VBAL §5.2.4.3).

VBClassModuleSymbol answers both sides of it: WithEventsVariables are the variables flagged with the WithEvents symbol property, and FindEventHandler(variable, event) is the procedure named for the variable and the event. It is the same naming that implements an interface member (RD-VBAL §5.3.1.9) and a lifecycle handler (RD-VBAL §5.3.1.10), and the only name a handler has: nothing calls it by name.

A handler is invalid when it is not a subroutine, or when its parameter list is not compatible with the event's: the same number of parameters, each of the same type and parameter mechanism. The parameters may differ in name, and in whether the mechanism is written out. ClassModuleEventSemantics reports it as VBC09326. It decides by the name alone: a procedure that only begins with a WithEvents variable's name and an underscore is no handler, and neither is one named for a variable that is not WithEvents; neither is checked.

Runtime Semantics

A handler is invoked by RaiseEvent (RD-VBAL §5.4.2.20) on the object that holds the event's source in the WithEvents variable, with that object as its target: its Me is the object that owns the variable, not the source.

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⏮️ RD-VBAL §5.3.1.7 Property Declarations | ⏭️ RD-VBAL §5.3.1.9 Implemented Name Declarations