System Messages

Declared in: app/AppDefs.h

B_MOUSE_WHEEL_CHANGED

Source: The system.

Target: The BWindow of the view the mouse is pointing to, and that of any other view that sets B_POINTER_EVENTS in its event mask (see BView::SetEventMask())

Hook: none

B_MOUSE_WHEEL_CHANGED is sent when the mouse wheel is distrubed. The message contains these fields:

Field	Type code	Description
"when"	B_INT64_TYPE	Event time, in microseconds since 01/01/70
"be:wheel_delta_x"	B_FLOAT_TYPE	The change in the wheel's horizontal position as a value between -1.0 (left) and 1.0 (right).
"be:wheel_delta_x"	B_FLOAT_TYPE	The change in the wheel's vertical position as a value between -1.0 (down) and 1.0 (up).

B_OBSERVER_NOTICE_CHANGE

Source: BHandler::SendNotices()

Target: Other BHandlers that are watching the notice-sender

Hook: none

B_OBSERVER_NOTICE_CHANGE is sent when the source object (a BHandler) invokes SendNotices(), which broadcasts a notice to all of its "watchers" (other BHandlers). A BHandler can register to be a watcher by calling BHandler::StartWatching().

Field	Type code	Description
B_OBSERVE_WHICH_CHANGE	B_INT32_TYPE	The change that caused the notification to be sent, as taken from an argument to SendNotices().
"be:old_what"	B_INT32_TYPE	The what field from the BMessage that's passed to SendNotices().
Other fields	...	The rest of the fields are copied from the message that's passed to SendNotices().

Channel Control Message

Source: A BChannelControl object

Target: Set through SetTarget() et al.

Hook: none

An n-channeled BChannelControl adds the following field to the BControl-defined value-changed message that it sends to its target.

Field	Type code	Description
"be:channel_value" [n]	B_INT32_TYPE	The value of each of the object's channels.

This field usurps (but doesn't remove) the "be:value" field that's added by BControl.