Windows SDK 两种消息类型(Message Types)的区别

System-Defined Messages

The system sends or posts a system-defined message when it communicates with an application. It uses these messages to control the operations of applications and to provide input and other information for applications to process. An application can also send or post system-defined messages. Applications generally use these messages to control the operation of control windows created by using preregistered window classes.

Each system-defined message has a unique message identifier and a corresponding symbolic constant (defined in the SDK header files) that states the purpose of the message. For example, the WM_PAINT constant requests that a window paint its contents.

Symbolic constants specify the category to which system-defined messages belong. The prefix of the constant identifies the type of window that can interpret and process the message. Following are the prefixes and their related message categories.

Prefix	Message category
ABM	Application desktop toolbar
BM	Button control
CB	Combo box control
CBEM	Extended combo box control
CDM	Common dialog box
DBT	Device
DL	Drag list box
DM	Default push button control
DTM	Date and time picker control
EM	Edit control
HDM	Header control
HKM	Hot key control
IPM	IP address control
LB	List box control
LVM	List view control
MCM	Month calendar control
PBM	Progress bar
PGM	Pager control
PSM	Property sheet
RB	Rebar control
SB	Status bar window
SBM	Scroll bar control
STM	Static control
TB	Toolbar
TBM	Trackbar
TCM	Tab control
TTM	Tooltip control
TVM	Tree-view control
UDM	Up-down control
WM	General window

 

General window messages cover a wide range of information and requests, including messages for mouse and keyboard input, menu and dialog box input, window creation and management, and dynamic data exchange (DDE).

 

 

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Application-Defined Messages

An application can create messages to be used by its own windows or to communicate with windows in other processes. If an application creates its own messages, the window procedure that receives them must interpret the messages and provide appropriate processing.

Message-identifier values are used as follows:

• The system reserves message-identifier values in the range 0x0000 through 0x03FF (the value of WM_USER – 1) for system-defined messages. Applications cannot use these values for private messages.
• Values in the range 0x0400 (the value of WM_USER) through 0x7FFF are available for message identifiers for private window classes.
• If your application is marked version 4.0, you can use message-identifier values in the range 0x8000 (WM_APP) through 0xBFFF for private messages.
• The system returns a message identifier in the range 0xC000 through 0xFFFF when an application calls the RegisterWindowMessage function to register a message. The message identifier returned by this function is guaranteed to be unique throughout the system. Use of this function prevents conflicts that can arise if other applications use the same message identifier for different purposes.