Messages Table of Contents | Messages Index

# General Messages

### B_ABOUT_REQUESTED

Purpose: Deliverable

Source: The system or your app.

Target: App-defined; typically `be_app`.

Hook: `BApplication::AboutRequested()` if the target is `be_app`.

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 , B_RELEASE_OVERLAY_LOCK

Source: A graphics driver.

Target: The team owning the overlay.

`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.

### B_APP_ACTIVATED

Purpose: Deliverable

Source: The system.

Target: `be_app`

Hook: `BApplication::AppActivated()`

Sent when an application becomes active or inactive.

Field | Type code | Description
"active" | `B_BOOL_TYPE` | `true` if the app has become active; otherwise `false`.

### B_ARCHIVED_OBJECT

Purpose: Deliverable and format

Source: A dragged replicant, or your app.

Target: A (remote) application.

Hook: `BShelf::CanAcceptReplicantMessage()`

As a deliverable: The replicant system uses this message as a deliverable. If you're using BDragger and BShelf objects, the message is created and delivered for you. You can also simulate a dragged replicant by archiving a view, setting the archive message's command to `B_ARCHIVED_OBJECT`, and sending the message to a remote application. If the remote application has a BShelf object, the BShelf will pick up the message (through a BMessageFilter) and pass it to the hook function.

To create a simulated replicant message, you call `Archive()` on the view that you want to replicate, and add (at least) the "add_on" field to the archive message.

See BShelf and BDragger for more information about replicants.

As a format: `B_ARCHIVED_OBJECT` should be used as the command constant for all archive messages. When you archive an object, the "class" field is automatically added to the archive message. All other fields must be added by your archiving code. See the BArchivable class for more information about archiving.

Field | Type code | Description
"class" [ ] | `B_STRING_TYPE` | An array of class names that gives the class hierarchy of the archived object.
"add_on" | `B_STRING_TYPE` | The signature of the library or application that knows how to create the archived object.
"be:add_on_version" | `B_INT32_TYPE` | The version of the add_on.
"be:load_each_time" | `B_BOOL_TYPE` | `true`: The add_on is loaded each time the object is unarchived. `false`: The add_on is loaded only if it isn't already loaded.
"be:unload_on_delete" | `B_BOOL_TYPE` | Is the add_on unloaded when the unarchived object is deleted?
"shelf_type" (replicants only; optional) | `B_STRING_TYPE` | The "type" of shelf that you want to have display the replicant. A shelf's type is its name, as assigned when it's created.

### B_ARGV_RECEIVED

Source: The system.

Target: `be_app`

Hook: `BApplication::ArgvReceived()`

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.

Field | Type code | Description
"argc" | `B_INT32_TYPE` | The number of arguments.
"argv" [argc] | `B_STRING_TYPE` | The arguments.
"cwd" | `B_STRING_TYPE` | The path name of the current working directory.

### B_CANCEL

Purpose: Deliverable

Source: The Application Kit.

Target: Application Server.

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.

### B_CLIPBOARD_CHANGED

Purpose: Deliverable

Source: The Application Server.

Target: Selected BMessenger.

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

### B_CONTROL_INVOKED

Purpose: Deliverable

Source: A BControl.

Target: Selected BMessenger.

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

### B_INPUT_DEVICES_CHANGED

Purpose: Deliverable

Source: The Input Server.

Target: Add-on specified target.

Hook: `BInput::Control()`

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.

Field | Type code | Description
"code" | `B_INT32_TYPE` | Operation code for the keyboard device control request being issued. One of: `B_INPUT_DEVICE_ADDED B_INPUT_DEVICE_STARTED B_INPUT_DEVICE_STOPPED B_INPUT_DEVICE_REMOVED`
"device" | `B_STRING_TYPE` | The name of the device. If this field doesn't exist, the device is identified by "type" instead.
"type" | `B_INT32_TYPE` | The device type. If this field doesn't exist, the "device" field identifies the device.
"message" | `B_MESSAGE_TYPE` | The control message. None of the BeOS standard messages use this field.

### B_INPUT_METHOD_EVENT

Purpose: Deliverable

Source: The Input Server.

Target: Input method add-on's BLooper.

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.

- `B_INPUT_METHOD_STARTED

  `
- `B_INPUT_METHOD_STOPPED

  `
- `B_INPUT_METHOD_CHANGED

  `
- `B_INPUT_METHOD_LOCATION_REQUEST

  `

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

### B_KEY_DOWN , B_KEY_UP , B_UNMAPPED_KEY_DOWN , B_UNMAPPED_KEY_UP

Source: The system.

Target: The focus view's BWindow.

Hook: `BView::KeyDown()` (`B_KEY_DOWN`)
`BView::KeyUp()` (`B_KEY_UP`)
(The `...UNMAPPED...` messages don't map to hook functions.)

`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.

Field | Type code | Description
"when" | `B_INT64_TYPE` | Event time, in microseconds since 01/01/70
"key" | `B_INT32_TYPE` | The code for the physical key that was pressed. See <x> for the key map.
"be:key_repeat" (`B_KEY_DOWN` only) | `B_INT32_TYPE` | The "iteration number" of this key down. When the user holds the key down, successive messages are sent with increasing key repeat values. This field isn't present in the initial event; the first repeat message (i.e., the second key down message) has a key repeat value of 1.
"modifiers" | `B_INT32_TYPE` | The modifier keys that were in effect at the time of the event. See <x> for a list of values.
"states" | `B_UINT8_TYPE` | The state of all keys at the time of the event. See <x>.
"byte" [3] (`B_KEY_DOWN` and `B_KEY_UP` only) | `B_INT8_TYPE` | The UTF8 data that's generated
"bytes" (`B_KEY_DOWN` and `B_KEY_UP` only) | `B_STRING_TYPE` | The string that's generated. (The string usually contains a single character.)
"raw_char" (`B_KEY_DOWN` and `B_KEY_UP` only) | `B_INT32_TYPE` | Modifier-independent ASCII code for the character.

### B_KEY_UP see B_KEY_DOWN

### B_KEYBOARD_DEVICE

Purpose: Deliverable

Source: The input server.

Target: A keyboard device add-on.

Hook: `BInput::Control()`

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

Field | Type code | Description
"code" | `B_INT32_TYPE` | Operation code for the keyboard device control request being issued. One of: `B_KEY_MAP_CHANGED B_KEY_LOCKS_CHANGED B_KEY_REPEAT_DELAY_CHANGED B_KEY_REPEAT_RATE_CHANGED`
"device" | `B_STRING_TYPE` | The name of the device. If this field doesn't exist, the device is identified by "type" instead.
"type" | `B_INT32_TYPE` | The device type. If this field doesn't exist, the "device" field identifies the device.
"message" | `B_MESSAGE_TYPE` | The control message for the request. None of the BeOS standard messages use this field.

### B_UNMAPPED_KEY_UP see B_KEY_DOWN

### B_MEDIA_BUFFER_CREATED , B_MEDIA_BUFFER_DELETED

Purpose: Deliverable

Source: The media server.

Target: Target specified to `BMediaRoster::StartWatching()`.

Sent to indicate that a media buffer has been created or deleted.

`B_MEDIA_BUFFER_CREATED`'s message has the following fields:

Field | Type Code | Description
"clone_info" | `B_RAW_TYPE` | An area_info structure describing the buffer's location in memory. This is an array, one entry per buffer created.

`B_MEDIA_BUFFER_DELETED` looks like this:

Field | Type Code | Description
"media_buffer_id" | `B_INT32_TYPE` | The buffer ID number of the buffer being deleted. This is an array, one entry per buffer deleted.

### B_MEDIA_BUFFER_DELETED see B_MEDIA_BUFFER_CREATED

### B_MEDIA_CONNECTION_BROKEN see B_MEDIA_CONNECTION_MADE

### B_MEDIA_CONNECTION_MADE , B_MEDIA_CONNECTION_BROKEN

Purpose: Deliverable

Source: The media server.

Target: Target specified to `BMediaRoster::StartWatching()`.

Sent to indicate that a connection between media nodes has been made or broken.

### B_MEDIA_FLAVORS_CHANGED

Purpose: Deliverable

Source: The media server.

Target: Target specified to `BMediaRoster::StartWatching()`.

Sent by the media server to indicate that the flavors supported by a particular add-on have changed.

Field | Type Code | Description
"be:addon_id" | `B_INT32_TYPE` | The add-on ID of the add-on whose flavors have changed
"be:new_count" | `B_INT32_TYPE` | How many new flavors have been added.
"be:gone_count" | `B_INT32_TYPE` | How many flavors have been removed.

### B_MEDIA_FORMAT_CHANGED

Purpose: Deliverable

Source: The media server.

Target: Target specified to `BMediaRoster::StartWatching()`.

Sent by the media server to indicate that the format used on a particular connection has changed.

Field | Type Code | Description
"be:source" | `B_RAW_TYPE` | A media_source structure describing the source of the connection whose format changed.
"be:destination" | `B_RAW_TYPE` | A media_source structure describing the source of the connection whose format changed.
"be:format" | `B_RAW_TYPE` | A media_format structure describing the new format.

### B_MEDIA_NODE_CREATED , B_MEDIA_NODE_DELETED

Purpose: Deliverable

Source: The media server.

Target: Target specified to `BMediaRoster::StartWatching()`.

Sent to indicate that a node has been created or deleted in the media system.

Field | Type Code | Description
"media_node_id" | `B_INT32_TYPE` | The ID of the media_node that was created or deleted.

### B_MEDIA_NODE_DELETED see B_MEDIA_NODE_CREATED

### B_MEDIA_NODE_STOPPED

Purpose: Deliverable

Source: The media server.

Target: Target specified to `BMediaRoster::StartWatching()`.

Indicates that a media node has stopped.

### B_MEDIA_PARAMETER_CHANGED , B_MEDIA_NEW_PARAMETER_VALUE

Purpose: Deliverable

Source: The media server.

Target: Target specified to `BMediaRoster::StartWatching()`.

Sent by the media server to indicate that the value of a parameter has changed. `B_MEDIA_PARAMETER_CHANGED` only tells you which parameter changed (media_node and parameter ID). `B_MEDIA_NEW_PARAMTER_VALUE` also tells you which parameter changed, and what the new value is.

The `B_MEDIA_PARAMETER_CHANGED` message looks like this:

Field | Type Code | Description
"be:node" | `B_RAW_TYPE` | A media_node structure indicating which node's parameter web has changed.
"be:parameter" | `B_INT32_TYPE` | The ID number of the parameter whose value has changed.

The `B_MEDIA_NEW_PARAMETER_VALUE` message is:

Field | Type Code | Description
"node" | `B_RAW_TYPE` | A media_node structure indicating which node is reporting a changed parameter value.
"parameter" | `B_INT32_TYPE` | The parameter ID of the changed parameter.
"when" | `B_INT64_TYPE` | The performance time at which the change took effect.
"value" | `B_RAW_TYPE` | The parameter's new value.

### B_MEDIA_WEB_CHANGED

Purpose: Deliverable

Source: The media server.

Target: Target specified to `BMediaRoster::StartWatching()`.

Sent by the media server to indicate that a particular node's BParameterWeb has.

Field | Type Code | Description
"node" | `B_RAW_TYPE` | A media_node structure indicating which node's parameter web has changed.

### B_MEDIA_WILDCARD

Purpose: Constant only.

Source: Your application.

Target: The media server.

When calling `BMediaRoster::StartWatching()` or `BMediaRoster::StopWatching()`, you can use this constant to match all media messages. This message has no actual format.

(No Be-defined fields)

### B_MINIMIZE

Source: The system or your app.

Target: The BWindow that's hidden/unhidden.

Hook: `BWindow::Minimize()`

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).

Field | Type code | Description
"when" | `B_INT64_TYPE` | Event time, in microseconds since 01/01/70.
"minimize" | `B_BOOL_TYPE` | `true` if the window is being hidden; `false` if it's being unhidden.

### B_MODIFIERS_CHANGED

Source: The system.

Target: The focus view's window.

Sent when the user presses or releases a modifier key.

Field | Type code | Description
"when" | `B_INT64_TYPE` | Event time, in microseconds since 01/01/70
"modifiers" | `B_INT32_TYPE` | The current modifier keys. See <x>
"be:old_modifiers" | `B_INT32_TYPE` | The previous modifier keys.
"states" | `B_UINT8_TYPE` | The state of all keys at the time of the event. See <x>.

### B_MOUSE_DOWN

Source: The system.

Target: The BWindow of the view the mouse is pointing to.

Hook: `BView::MouseDown()`

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

Field | Type code | Description
"when" | `B_INT64_TYPE` | Event time, in microseconds since 01/01/70
"where" | `B_POINT_TYPE` | Mouse location in the view's coordinate system.
"modifiers" | `B_INT32_TYPE` | The # modifier keys that were in effect at the time of theevent.
"buttons" | `B_INT32_TYPE` | The mouse button that was pressed, one of: `B_PRIMARY_MOUSE_BUTTON B_SECONDARY_MOUSE_BUTTON B_TERTIARY_MOUSE_BUTTON`
"clicks" | `B_INT32_TYPE` | 1 for a single-click, 2 for double-click, 3 for triple-click, and so on. The counter is reset if the time between clicks exceeds the "Double-click speed" set by the user in the Mouse preferences. Note that the counter is not reset if the mouse moves between clicks.

### B_MOUSE_MOVED

Source: The system.

Target: The BWindow of the view the mouse is pointing to.

Hook: `BView::MouseMoved()`

Sent when the user moves the mouse.

Field | Type code | Description
"when" | `B_INT64_TYPE` | Event time, in microseconds since 01/01/70
"where" | `B_POINT_TYPE` | The mouse's new location in window coordinates.
"buttons" | `B_INT32_TYPE` | The mouse buttons that are down. Zero or more of: `B_PRIMARY_MOUSE_BUTTON B_SECONDARY_MOUSE_BUTTON B_TERTIARY_MOUSE_BUTTON`

### B_MOUSE_UP

Source: The system.

Target: The BWindow of the view the mouse is pointing to.

Hook: `BView::MouseUp()`

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

Field | Type code | Description
"when" | `B_INT64_TYPE` | Event time, in microseconds since 01/01/70
"where" | `B_POINT_TYPE` | Mouse location in the view's coordinate system.
"modifiers" | `B_INT32_TYPE` | The modifier keys that were in effect at the time of the event. See <x> for a list of modifier values.

### B_MOUSE_WHEEL_CHANGED

Source: The system.

Target: The BWindow of the view the mouse is pointing to.

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

Field | Type code | Description
"when" | `B_INT64_TYPE` | Event time, in microseconds since 01/01/70
"be:wheel_delta_x" | `B_FLOAT_TYPE` | How much the Y value of the wheel has changed.
"be:wheel_delta_y" | `B_FLOAT_TYPE` | How much the Y value of the wheel has changed.

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

### B_NODE_MONITOR

Source: The Node Monitor.

Target: App-defined.

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:

- `B_ENTRY_CREATED

  `
- `B_ENTRY_REMOVED

  `
- `B_ENTRY_MOVED

  `
- `B_STAT_CHANGED

  `
- `B_ATTR_CHANGED

  `
- `B_DEVICE_MOUNTED

  `
- `B_DEVICE_UNMOUNTED

  `

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

### B_OBSERVER_NOTICE_CHANGE

Source: The system.

Target: Application-defined target.

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

Field | Type code | Description
"be:observe_change_what" | `B_INT32_TYPE` | The "what" code of the message being broadcast.
"be:observe_orig_what" | `B_INT32_TYPE` | The original "what" code of the message, before it was altered by the broadcasting mechanism.

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:

- Take the message to broadcast and place its what code into the "be:observe_change_orig_what" field.

- Add the "be:observe_change_what" field, which is set to the what code specified by the call to `SendNotices()`.

- Set the message's what code to `B_OBSERVER_NOTICE_CHANGE`.

The resulting message is then sent to all interested parties.

See also: `BHandler::SendNotices()`, `BHandler::StartWatching()`

### B_OPEN_IN_WORKSPACE

Source: The system.

Target: BApplication.

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.

Field | Type code | Description
"be:workspace" | `B_INT32_TYPE` | Workspace number into which the application should open.

### B_POINTING_DEVICE

Purpose: Deliverable

Source: The input server.

Target: A pointing device add-on.

Hook: `BInput::Control()`

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

Field | Type code | Description
"code" | `B_INT32_TYPE` | Operation code for the pointing device control request being issued. One of: `B_MOUSE_TYPE_CHANGED B_MOUSE_MAP_CHANGED B_MOUSE_SPEED_CHANGED B_CLICK_SPEED_CHANGED B_MOUSE_ACCELERATION_CHANGED`
"device" | `B_STRING_TYPE` | The name of the device. If this field doesn't exist, the device is identified by "type" instead.
"type" | `B_INT32_TYPE` | The device type. If this field doesn't exist, the "device" field identifies the device.
"message" | `B_MESSAGE_TYPE` | The control message for the request. None of the BeOS standard messages use this field.

### B_PRINTER_CHANGED

Source: The Print Server.

Target: Everyone.

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.

### B_PULSE

Source: The system.

Target: `be_app` or BWindow object.

Hook: `BApplication::Pulse()` and `BView::Pulse()`

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.

### B_QUERY_UPDATE

Source: The system.

Target: App-defined.

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.

### B_QUIT_REQUESTED

Source: The system or your app.

Target: `be_app`, BWindow closed by the user, or other`` BLooper object.

Hook: `BLooper::QuitRequested()`.

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.

Field | Type code | Description
"shortcut" | `B_BOOL_TYPE` | true if the user typed Command+q.

### B_READY_TO_RUN

Source: The system.

Target: `be_app`

Hook: `BApplication::ReadyToRun()`

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

(No Be-defined fields)

### B_REFS_RECEIVED

Source: The system or your app.

Target: `be_app`, or other app-defined target.

Hook: `BApplication::RefsReceived()`

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.

Field | Type code | Description
"refs" [i] | `B_REF_TYPE` | `entry_ref` items, one for each file or directory.

`` A BStatusBar object can be controlled synchronously by calling its `Reset()` and `Update()` functions. It can also be controlled asynchronously by sending it messages corresponding to the two functions; the object calls the function when it receives the message. Each message contains fields for the arguments passed to the function.

### B_RELEASE_OVERLAY_LOCK see B_ACQUIRE_OVERLAY_LOCK

### B_RESET_STATUS_BAR

Source: Your app.

Hook: `BStatusBar::Reset()`

Target: The BStatusBar you're resetting.

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);

Field | Type code | Description
"label" | `B_STRING_TYPE` | The object's new label (`NULL`-terminated).
"trailing_label" | `B_STRING_TYPE` | The object's new trailing label (`NULL`-terminated)..

### B_SCREEN_CHANGED

Source: The system.

Target: Every BWindow in the screen that changed (even hidden windows).

Hook: `BWindow::ScreenChanged()`

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

Field | Type code | Description
"when" | `B_INT64_TYPE` | Event time, in microseconds since 01/01/70
"frame" | `B_RECT_TYPE` | The screen's dimensions.
"mode" | `B_INT32_TYPE` | The screen's color space: `B_CMAP8`, `B_RGB15`, `B_RGB15`, or `BRGB32`.

### B_SILENT_RELAUNCH

Source: The system.

Target: `be_app`

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)

### B_SOME_APP_ACTIVATED , B_SOME_APP_LAUNCHED , B_SOME_APP_QUIT

Source: The Roster Monitor.

Target: App-defined.

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`.

Field | Type code | Description
"mime_sig" | `B_STRING_TYPE` | The ap signature.
"team" | `B_INT32_TYPE` | The app's team id.
"thread" | `B_INT32_TYPE` | The id of the app's main thread.
"flags" | `B_INT32_TYPE` | The app's app flags (`B_SINGLE_LAUNCH`, `B_BACKGROUND_APP`, etc).
"ref" | `B_REF_TYPE` | The `entry_ref` of the app's executable.

### B_UPDATE_STATUS_BAR

Source: Your app.

Hook: `BStatusBar::Update()`

Target: The BStatusBar you're updating.

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);

Field | Type code | Description
"delta" | `B_FLOAT_TYPE` | An increment to the object's current value.
"text" | `B_STRING_TYPE` | The object's new text (`NULL`-terminated).
"trailing_text" | `B_STRING_TYPE` | The object's new trailing text (`NULL`-terminated)..

### B_VALUE_CHANGED

Source: The system.

Target: The manipulated scrollbar's BWindow.

Hook: `BScrollBar::ValueChanged()`

Sent when the user plays with a scrollbar.

Field | Type code | Description
"when" | `B_INT64_TYPE` | Event time, in microseconds since 01/01/70
"value" | `B_INT32_TYPE` | The scrollbar's new value.

### B_VIEW_MOVED

Source: The system.

Target: The moved view's BWindow.

Hook: `BView::FrameMoved()`

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.

Field | Type code | Description
"when" | `B_INT64_TYPE` | Event time, in microseconds since 01/01/70
"where" | `B_POINT_TYPE` | The view's new origin in the coordinate system of its parent.

### B_VIEW_RESIZED

Source: The system.

Target: The resized view's BWindow.

Hook: `BView::FrameResized()`

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.

Field | Type code | Description
"when" | `B_INT64_TYPE` | Event time, in microseconds since 01/01/70
"width" | `B_INT32_TYPE` | The view's new width.
"height" | `B_INT32_TYPE` | The view's new height.
"where" | `B_POINT_TYPE` | The view's new origin expressed in the coordinate system of its parent. This field is only included if the view actually moved while being resized, and can always be ignored: If the view did move, you'll hear about it in a separate `B_VIEW_MOVED` BMessage.

### B_WINDOW_ACTIVATED

Source: The system.

Target: The activated/deactivated BWindow.

Hook: `BWindow::WindowActivated()` and `BView::WindowActivated()`

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

Field | Type code | Description
"when" | `B_INT64_TYPE` | Event time, in microseconds since 01/01/70
"active" | `B_BOOL_TYPE` | `true` if the window is now active; `false` if not.

### B_WINDOW_MOVE_BY

Purpose: Deliverable.

Source: Your application.

Target: The BWindow to be moved.

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

Field | Type code | Description
"data" | `B_POINT_TYPE` | The amount by which to move the window's X and Y coordinates.

### B_WINDOW_MOVE_TO

Purpose: Deliverable.

Source: Your application.

Target: The BWindow to be moved.

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

Field | Type code | Description
"data" | `B_POINT_TYPE` | The width and height (in X and Y) to resize the window to.

### B_WINDOW_MOVED

Source: The system.

Target: The BWindow that moved.

Hook: `BWindow::FrameMoved()`

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

Field | Type code | Description
"when" | `B_INT64_TYPE` | Event time, in microseconds since 01/01/70
"where" | `B_POINT_TYPE` | The window's new origin in screen coordinates.

### B_WINDOW_RESIZED

Source: The system.

Target: The resized BWindow.

Hook: `BWindow::FrameResized()`

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.

Field | Type code | Description
"when" | `B_INT64_TYPE` | Event time, in microseconds since 01/01/70
"width" | `B_INT32_TYPE` | The width of the window's content area.
"height" | `B_INT32_TYPE` | The height of the window's content area.

### B_WORKSPACE_ACTIVATED

Source: The system.

Target: Every BWindow in the activated and deactivated workspaces.

Hook: `BWindow::WorkspaceActivated()`

Sent when the active workspace changes.

Field | Type code | Description
"when" | `B_INT64_TYPE` | Event time, in microseconds since 01/01/70
"workspace" | `B_INT32_TYPE` | The index of the window's workspace.
"active" | `B_BOOL_TYPE` | `true` if the workspace is now active; `false` if not.

### B_WORKSPACES_CHANGED

Source: The system.

Target: The BWindow whose set of workspaces changed.

Hook: `BWindow::WorkspacesChanged()`

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

Field | Type code | Description
"when" | `B_INT64_TYPE` | Event time, in microseconds since 01/01/70
"old" | `B_INT32_TYPE` | The window's old workspace set, given as a vector of workspace indices.
"new" | `B_INT32_TYPE` | The window's new workspace set, given as a vector of workspace indices.

### B_ZOOM

Source: The system.

Target: The BWindow that was zoomed.

Hook: `BWindow::Zoom()`

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

The message has just one data field:

Field | Type code | Description
"when" | `B_INT64_TYPE` | Event time, in microseconds since 01/01/70

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