__hook keyword

Associates a handler method with an event.

Note

Event attributes in native C++ are incompatible with Standard C++. They don't compile when you specify /permissive- conformance mode.

Syntax

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

long __hook(
    interface,
    source
);

Parameters

&SourceClass::EventMethod
A pointer to the event method to which you hook 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 hooked to 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 these types:

• 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 hooked to an event. The handler is specified as a method of a class or a reference to the same. If you don't specify the class name, __hook assumes the class is the one it's called from.

• 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 don't specify a receiver, the default is the receiver class or structure in which __hook is called.

Usage

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

Remarks

Use the intrinsic function __hook in an event receiver to associate or hook a handler method with an event method. The specified handler is then called when the source raises the specified event. You can hook several handlers to a single event or hook several events to a single handler.

There are two forms of __hook. You can use the first (four-argument) form in most cases, specifically, for COM event receivers in which the layout_dependent parameter of the event_receiver attribute is false.

In these cases, you don't need to hook all methods in an interface before firing an event on one of the methods. You only need to hook the method handling the event. You can use the second (two-argument) form of __hook only for a COM event receiver in which layout_dependent = true.

__hook returns a long value. A nonzero return value indicates that an error has occurred (managed events throw an exception).

The compiler checks for the existence of an event and that the event signature agrees with the delegate signature.

You can call __hook and __unhook outside the event receiver, except for COM events.

An alternative to using __hook 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.

See also

Keywords
Event handling
event_source
event_receiver
__event
__unhook
__raise