__unhook

Artikel
01/03/2018

The latest version of this topic can be found at __unhook.

Dissociates a handler method from an event.

Syntax

  
      long  __unhook(  
   &SourceClass::EventMethod,  
   source,  
   &ReceiverClass::HandlerMethod  
   [, receiver = this]   
);  
long  __unhook(   
   interface,  
   source  
);  
long  __unhook(  
   source   
);

Parameters

& SourceClass :: EventMethod
A pointer to the event method from which you unhook the event handler method:

Native C++ events: SourceClass is the event source class and EventMethod is the event.
COM events: SourceClass is the event source interface and EventMethod is one of its methods.
Managed events: SourceClass is the event source class and EventMethod is the event.

interface
The interface name being unhooked from receiver, only for COM event receivers in which the layout_dependent parameter of the event_receiver attribute is true.

source
A pointer to an instance of the event source. Depending on the code type specified in event_receiver, source can be one of the following:

A native event source object pointer.
An IUnknown-based pointer (COM source).
A managed object pointer (for managed events).

& ReceiverClass :: HandlerMethod
A pointer to the event handler method to be unhooked from an event. The handler is specified as a method of a class or a reference to the same; if you do not specify the class name, __unhook assumes the class to be that in which it is called.

Native C++ events: ReceiverClass is the event receiver class and HandlerMethod is the handler.
COM events: ReceiverClass is the event receiver interface and HandlerMethod is one of its handlers.
Managed events: ReceiverClass is the event receiver class and HandlerMethod is the handler.

receiver(optional)
A pointer to an instance of the event receiver class. If you do not specify a receiver, the default is the receiver class or structure in which __unhook is called.

Usage

Can be use in any function scope, including main, outside the event receiver class.

Remarks

Use the intrinsic function __unhook in an event receiver to dissociate or "unhook" a handler method from an event method.

There are three forms of __unhook. You can use the first (four-argument) form in most cases. You can use the second (two-argument) form of __unhook only for a COM event receiver; this unhooks the entire event interface. You can use the third (one-argument) form to unhook all delegates from the specified source.

A nonzero return value indicates that an error has occurred (managed events will throw an exception).

If you call __unhook on an event and event handler that are not already hooked, it will have no effect.

At compile time, the compiler verifies that the event exists and does parameter type checking with the specified handler.

With the exception of COM events, __hook and __unhook can be called outside the event receiver.

An alternative to using __unhook is to use the -= operator.

For information on coding managed events in the new syntax, see event.

Note

A templated class or struct cannot contain events.

Example

See Event Handling in Native C++ and Event Handling in COM for samples.

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