Deeply parse messages in VC (on)

Abstract: Windows Programming and DOS programming, a big difference is that Windows programming is event-driven, message transmission. Therefore, to do a good job in Windows programming, you must have a clear understanding of the message mechanism. This article hopes to make a comprehensive discussion of message transmission, there may be some mistakes in it. I also criticize and correct them.

What is a message?
The message system is very important for a Win32 program. It is the source of motivation for running programs. A message is a 32-bit value defined by the system. It uniquely defines an event and sends a notification to Windows to tell the application that something has happened. For example, if you click the mouse, change the window size, or press a key on the keyboard, Windows will send a message to the application.
The message itself is passed to the application as a record, which contains the Message Type and other information. For example, for a message generated by clicking the mouse, this record contains the coordinates of the mouse. This record type is MSG. MSG contains message information from the Windows application message queue. It declares the following in Windows:
Typedef struct tagmsg
{
Hwnd; the window handle that receives the message
Uint message; the constant identifier of the message, which is the message number.
Wparam; a 32-bit additional message. The exact meaning depends on the message value.
Lparam; a 32-bit additional message. The exact meaning depends on the message value.
DWORD time; the time when the message was created
Point pt; cursor/cursor position in the screen coordinate system when a message is created
} MSG;
Messages can be generated by the system or application. The system generates a message when an input event occurs. For example, when you press the key, move the mouse or click the control. The system also generates messages to respond to changes caused by applications. For example, the application changes the system font and changes the form size. Applications can generate messages to execute tasks in the form or communicate with windows in other applications.

What are messages?
We have provided the above comments. Do we have a clear understanding of the message structure? If not, let's try again to explain the following:
Hwnd 32-bit window handle. Windows can be any type of screen objects, because Win32 can maintain the handles of most visual objects (Windows, dialog boxes, buttons, edit boxes, etc ).
Message is used to distinguish the constant values of other messages. These constants can be pre-defined constants in Windows units or custom constants. The message identifier indicates the meaning of a message in the form of a constant name. After a message is received in the window process, the message identifier is used to determine how to process the message. For example, wm_paint tells the window that the form customer area needs to be re-painted when it is changed. A symbolic constant specifies the type of the system message. Its prefix specifies the type of the form for processing the interpreted message.
Wparam is a message-related constant value, or a handle to a window or control.
Lparam is usually a pointer to data in the memory. Since wparam, lparam, and pointer are both 32-bit, they can be converted to each other.

Message Identifier value
The system retains the message Identifier value in the 0x0000 range in 0x03ff (WM_USER-1. These values are used by system-defined messages. Applications cannot use these values for their own messages. The application uses messages from wm_user (0x0400) to 0x7fff, or 0xc000 to 0 xFFFF; Messages from wm_user to 0x7fff are used by the application itself; messages in the range from 0xc000 to 0xffff are used to communicate with other applications. By the way, we have a symbolic message value:
Wm_null --- 0x0000 empty message.
0x0001 ---- 0x0087 is mainly a window message.
0x00a0 ---- 0x00a9 non-customer zone message
0x0100 ---- 0x0108 Keyboard Message
0x0111 ---- 0x0126 menu message
0x0132 ---- 0x0138 Color Control Message
0x0200 ---- 0x020a mouse message
0x0211 ---- 0x0213 menu cyclic message
0x0220 ---- 0x0230 multi-document message
0x03e0 ---- 0x03e8 DDE message
0x0400 wm_user
0x8000 wm_app
0x0400 ---- 0x7fff application custom private message

What types of messages are there?
In fact, there are many messages in windows, but the types are not complicated. There are generally three types: Window messages, command messages, and control notification messages.
Window messages are the most common messages in the system. They are the messages used by the operating system and windows that control other windows. For example, createwindow, destroywindow, and movewindow will trigger window messages, and the messages generated by clicking the mouse we have discussed above are also window messages.
Command message, which is a special window message. It is used to process user requests sent from one window to another. For example, if you press a button, it will send a command message to the main window.
A control notification message refers to a message in which a child control in a window has something to notify the parent window. The notification message is only applicable to standard window controls such as buttons, list boxes, Combo boxes, and edit boxes, as well as windows public controls such as tree views and list views. For example, clicking or double-clicking a control, selecting some text in the control, and the scroll bar of the operation control will generate a notification message. It is similar to a command message. When the user interacts with the control window, the control notification message is sent from the control window to its main window. However, this message does not exist to process user commands, but to enable the main window to change controls, such as loading and displaying data. For example, if you press a button, the message sent to the parent window can also be considered as a control notification message. The message generated by clicking the mouse can be processed directly by the main window and then handed over to the control window for processing.
The window messages and control notification messages are processed directly or indirectly by the cwnd class derived class. Compared with window messages and control notification messages, a command message can process a wide range of objects. It can be processed by window classes, document classes, document templates, and application classes.
Because the control notification message is very important and many people use it, but the specific meaning is often confusing for beginners, I decided to list the common ones for your reference:
Button Control
The bn_clicked user clicked the button.
Bn_disable button disabled
Bn_doubleclicked double-click the button
Bn_hilite user/user highlighted button
Bn_paint button should be repainted
Bn_unhilite should be removed
Combo Control
The list box of the cbn_closeup combo box is closed.
The cbn_dblclk user double-clicked a string.
The list box of the cbn_dropdown combo box is pulled out.
The cbn_editchange user modified the text in the editing box.
The text in the cbn_editupdate edit box is about to be updated.
The cbn_errspace combo box has insufficient memory.
The cbn_killfocus combo box loses the input focus.
Cbn_selchange
Cbn_selendcancel user selection should be canceled
Cbn_selendok users' selection is legal
Cbn_setfocus combo box to get the input focus
Edit box Control
The text in the en_change edit box has been updated.
The en_errspace editing box has insufficient memory.
The en_hscroll user clicked the horizontal scroll bar.
The en_killfocus edit box is missing the input focus.
The content inserted by en_maxtext is truncated.
En_setfocus edit box to get the input focus
The text in the en_update edit box will be updated.
The en_vscroll user clicks the vertical scroll bar message meaning
List box Control
Lbn_dblclk
Lbn_errspace: insufficient memory in the list box
The lbn_killfocus list box is missing the input focus.
Lbn_selcancel selected to be canceled
Lbn_selchange selects another item
Lbn_setfocus list box to get the input focus

Unfinished (To be continued ...)