Removes a method or procedure as a handler for an ABL or .NET class event.
Return type: VOID
Access: PUBLIC
Applies to: ABL or .NET class events
Syntax
[ publisher : ] event-name:Unsubscribe
( [ subscriber : ] handler-method ) [ NO-ERROR ]
|
[ publisher : ] event-name:Unsubscribe
( [ subscriber-handle , ] handler-procedure ) [ NO-ERROR ]
|
- [
publisher : ]
- The object reference to an ABL or .NET object or the type name
of an ABL or .NET class that can publish the instance or static
event, respectively. If you do not specify a publisher,
it defaults to either THIS-OBJECT when event-name identifies
an instance event defined in the current class instance, or to the
class type name of the current class definition when event-name identifies
a static event defined in the current class hierarchy.
-
event-name
- The name of an ABL or .NET event that publisher can
publish. At compile time, ABL verifies that event-name is
an accessible member of the class referenced by publisher.
The event can be an abstract event.
- [
subscriber : ]
handler-method
- An ABL class-based method that you want to remove as a handler for event-name,
where handler-method is the unquoted name of
the instance or static method. If specified, subscriber can
be either the object reference to an ABL class instance where handler-method is
defined, or the type name of an ABL class where the static handler-method is defined.
If you do not specify a subscriber, it defaults
to THIS-OBJECT when handler-method identifies
an instance method defined in the current class hierarchy, or to the
class type name of the current class definition when handler-method identifies
a static method defined in the current class hierarchy.
Note that
the access mode (PUBLIC, PROTECTED, or PRIVATE) of the handler-method definition
does not matter to the publisher. For example,
you can remove a PRIVATE method of the unsubscribing class instance
as a handler for an event defined and published by yet another class
instance.
The signature of handler-method must
be run-time compatible with the signature defined for event-name.
This includes an overloaded method as long as ABL can identify the
signature for a unique overloading that is compatible with the event
signature.
Thus, ABL raises a compile-time error if handler-method:
- Is not accessible to the context where this Unsubscribe( ) method
executes
- Does not have a run-time compatible signature
- Does not have a unique overloading that is compatible with the
event signature
- [
subscriber-handle , ]
handler-procedure
- A procedure that you want to remove as a handler for event-name,
where handler-procedure is a character expression
that evaluates to the name of an internal procedure. If specified, subscriber-handle is
a handle to a persistent procedure, or other external procedure
on the call stack, where the internal procedure is defined. Otherwise, subscriber-handle defaults
to THIS-PROCEDURE.
At compile-time, ABL checks this Unsubscribe( ) method
call only to verify that any specified subscriber-handle is
a HANDLE data type and that handler-procedure is
specified by a character expression. Otherwise, ABL raises a run-time
error if the procedure context specified by subscriber-handle is
not accessible or it does not define handler-procedure as
an internal procedure.
- NO-ERROR
- The NO-ERROR option is used to
prevent the statement from raising ERROR and
displaying error messages.
The Unsubscribe( ) method
cancels an event subscription by removing the specified method or
internal procedure from the list of handlers for the specified event-name.
If you do not specify a publisher, you can only
invoke Unsubscribe( ) in an ABL class
definition and on an ABL or .NET event that the ABL class defines
or inherits. When you cancel an event handler subscription, ABL
does not raise either a run-time error if the specified event handler
is not currently on the subscription list for the specified event.
