The message should be assigned to an About... menu item, such that the message is sent when the user clicks the item. Your application is expected to put up an "About This Application" panel when it receives this message.

B_ACQUIRE_OVERLAY_LOCK is sent by a graphics driver when an overlay is acquired. B_RELEASE_OVERLAY_LOCK is sent when the overlay is released.

Sent when an application becomes active or inactive.

Forwards arguments that (a) the user passes while launching the app from the command line, or (b) are passed to BRoster::Launch(). Most apps treat command line arguments as filenames that should be opened. If the filename is relative (if it doesn't start with "/"), you should append it to the cwd field to reconstruct the full path.

Used to cancel an ongoing operation. The Application Kit sends this message to the Application Server to cancel a shutdown if a window refuses to quit.

If you've called BClipboard::StartWatching() to monitor a clipboard for changes, this message is sent to the specified BMessenger when the clipboard changes.

This message is sent to the targeted messenger when a BControl-derived object is invoked.

This message is sent by the Input Server to send you notification when a device starts or stops, or when the set of registered devices changes. These messages are sent only if you've used the watch_input_devices() function to request such notification. The messages are sent to the target indicated in the function call.

This message is sent by the Input Server to an input method add-on to let it know that a method event has occurred. The message's be:opcode field indicates which event has occurred.

These are discussed in more detail in the Input Server chapter.

B_KEY_DOWN is sent when the user presses (or holds down) a key that's mapped to a character; B_KEY_UP is sent when the user releases the key. B_UNMAPPED_KEY_DOWN and B_UNMAPPED_KEY_UP are sent if the key isn't mapped to a character. This doesn't include modifier keys, which are reported in the B_MODIFIERS_CHANGED message.

This message is used by the input server to send a request to a keyboard device add-on.

Sent when the user double-clicks a window's title bar (to hide the window), or selects a window from the DeskBar's window list (to unhide the window).

Sent when the user presses or releases a modifier key.

Sent when the user presses a mouse button. This message is only sent if no other mouse button is already down.

Sent when the user moves the mouse.

Sent when the user releases a mouse button. It's only sent if no other mouse button remains down.

Sent when the user moves the mouse wheel (on mice that have them).

The standard mouse driver that comes with BeOS only supports a Y-oriented wheel.

Sent when a monitored file changes. All Node Monitor messages contain an int32 opcode field that tells you what happened (a file was removed, an attribute changed, etc.). The format of the rest of the message depends on the opcode. The formats are given under individual entries in this appendix, listed by opcode value:

These are discussed in the section "The Node Monitor".

Sent by BHandlers to all targets that have been registered with the BHandler's StartWatching() or StartWatchingAll() function.

The message may have other fields, depending on what the broadcast message is. Messages are sent to targets in response to the BHandler::SendNotices() function. The logic is:

The resulting message is then sent to all interested parties.

Sent to an application when it's first launched to tell it to open in a specific workspace. The message will be handled during the construction of the BApplication object.

This message is used by the input server to send a request to a pointing device add-on.

Sent whenever the user changes printers. Applications that support printing should watch for this message, and if they receive it, they should suggest that the user check their page setup the next time they choose to print.

Sent at regular intervals, but with no particular intent. You can implement Pulse() to do whatever you want. The message is to the BWindow only if a BView within the window declares B_PULSE_NEEDED in its constructor flags.

Sent when the results of a live query change: If a new file meets the query requirements, B_ENTRY_CREATED is sent. If a file that previously passed the query requirements no longer does, B_ENTRY_REMOVED is sent.

Automatically sent (a) to be_app when the user types Command+q, and (b) to a BWindow when the user clicks the window's close box. Applications can also manufacture and send the message themselves. A looper that receives this message is expected to quit, or at least consider quitting.

Sent when an application has finished configuring itself and is ready to start running.

(No Be-defined fields)

Automatically sent to be_app when (a) the user double-clicks a file that has a type that's supported by the app, and (b) when the user confirms some files (or directories) in an Open File panel (the target is be_app by default; it can be changed in BFilePanel::SetTarget()). You can also create, stuff, and send a B_REFS_RECEIVED message yourself. When it receives this message, an app is expected to open the files that the message refers to.

You construct and send this message to a BStatusBar object to tell it to (asynchronously) reset itself. The message also lets you reset the object's labels. To send the message, invoke BWindow's PostMessage() naming the target BStatusBar as the handler:

statusBar->Window()->PostMessage(theMessage, statusBar);

Sent when the screen's dimensions or color space changes—because the user played with the Screen preferences app, for example.

Sent to a single-launch application when it's activated by being launched (for example, if the user double-clicks its icon in Tracker).

(No Be-defined fields)

Sent as apps are launched, activated, or quit. You get these messages by invoking BRoster::StartWatching() passing a one or more of B_REQUEST_ACTIVATED, B_REQUEST_LAUNCHED, and B_REQUEST_QUIT.

You construct and send this message to a BStatusBar object to tell it to (asynchronously) update its progress. To send the message, invoke BWindow's PostMessage() naming the target BStatusBar as the handler:

statusBar->Window()->PostMessage(theMessage, statusBar);

Sent when the user plays with a scrollbar.

Sent when a view's origin (left top corner) changes relative to the origin of its parent. The message isn't sent if the view doesn't have the B_FRAME_EVENTS flag set.

Sent when the size of the view's frame changes. The message isn't sent if the view doesn't have the B_FRAME_EVENTS flag set.

Sent just after a window is activated or deactivated. Note that the BWindow invokes WindowActivated() on each of its views.

You can send this message to a window to resize it by the specified deltas.

You can send this message to a window to resize it to the specified size.

Sent when a window's origin (left top corner) changes within the screen coordinate system.

Sent when the size of the window's frame changes. Note that the width and height fields measure the window's content area—they don't include the window border or window tab.

Sent when the active workspace changes.

Sent when there's a change to the set of workspaces in which a window can appear.

Sent when the user clicks a window's zoom button.

The message has just one data field: