A Window with a Button

Consider the first example. When you start this program, a window with an Exit button will appear. As you clearly understand, pressing this button terminates the program.

The most important thing here is how the program is informed that the button has been clicked. Everything is simple: First, it is necessary to check the WM_COMMAND message; then, you must check LPARAM containing the window descriptor (the unique number, called handle). The button is created in the form of the window. In this case, for the button, it is sufficient to define an event. ^[i]

Pay special attention to the button that you are creating. This combination of properties is the most typical but is not the only possible one. For example, if you want a button to contain an icon, you'll have to specify the BS_ICON (or BS_BITMAP ) property for it.

Listing 3.1: A window with an Exit button

 ; The button.inc file ; Constants ; The message that arrives when the window is closed WM_DESTROY                 equ 2 ; The message that arrives when the window is opened WM_CREATE                  equ 1 ; The message that arrives when the user ; clicks the left mouse button in the window area WM_LBUTTONDOWN             equ 201h WM_COMMAND                 equ 111h ; Window properties CS_VREDRAW                 equ  1h CS_HREDRAW                 equ 2h CS_GLOBALCLASS             equ 4000h WS_OVERLAPPEDWINDOW        equ 000CF0000H STYLE                      equ CS_HREDRAW+CS_VREDRAW+CS_GLOBALCLASS BS_DEFPUSHBUTTON           equ 1h WS_VISIBLE                 equ 10000000h WS_CHILD                   equ 40000000h STYLBTN                    equ WS_CHILD+BS_DEFPUSHBUTTON+WS_VISIBLE ; Standard icon identifier IDI_APPLICATION            equ 32512 ; Cursor identifier IDC_ARROW                  equ 32512 ; Normal mode of displaying the window SWJ_SHOWNORMAL             equ 1 ; Prototypes of external procedures EXTERN MessageBoxA@16:NEAR EXTERN CreateWindowExA@ 48:NEAR EXTERN DefWindowProcA@16:NEAR EXTERN DispatchMessageA@4:NEAR EXTERN ExitProcess@4:NEAR EXTERN GetMessageA@16:NEAR EXTERN GetModuleHandleA@4:NEAR EXTERN LoadCursorA@8:NEAR EXTERN LoadIconA@8:NEAR EXTERN PostQuitMessage@4:NEAR EXTERN RegisterClassA@4:NEAR EXTERN ShowWindow@8:NEAR EXTERN TranslateMessage@4:NEAR EXTERN UpdateWindow@4:NEAR ; Structure ; Message structure MSGSTRUCT STRUC     MSHWND          DD ?     MSMESSAGE       DD ?     MSWPARAM        DD ?     MSLPARAM        DD ?     MSTIME          DD ?     MSPT            DD ? MSGSTRUCT ENDS ;---- Window class structure WNDCLASS STRUC     CLSSTYLE        DD ?     CLWNDPROC       DD ?     CLSCBCLSEX      DD ?     CLSCBWNDEX      DD ?     CLSHINST        DD ?     CLSHICON        DD ?     CLSHCURSOR      DD ?     CLBKGROUND      DD ?     CLMENNAME       DD ?     CLNAME          DD ? WNDCLASS ENDS ; The button.asm file .586P ; Flat memory model .MODEL FLAT, stdcall include button.inc ; Directives for the linker to link libraries includelib c:\masm32\lib\user32.lib includelib c:\masm32\lib\kernel32.lib ;------------------------------------------ ; Data segment _DATA SEGMENT DWORD PUBLIC USE32 'DATA'     NEWHWND         DD 0     MSG             MSGSTRUCT <?>     WC              WNDCLASS  <?>     HINST           DD 0 ; Application descriptor     TITLENAME       DB 'The example - Exit button', 0     CLASSNAME       DB 'CLASS32', 0     CPBUT           DB 'Exit', 0 ; Exit     CLSBUTN         DB 'BUTTON', 0     HWNDBTN         DWORD 0     CAP             DB 'Message', 0     MES             DB 'Program termination', 0 _DATA ENDS ; Code segment _TEXT SEGMENT DWORD PUBLIC USE32 'CODE' START: ; Get the application descriptor     PUSH            0     CALL            GetModuleHandleA@4     MOV             [HINST], EAX ; REG_CLASS: Fill the window structure ; Style     MOV             [WC.CLSSTYLE], STYLE ; Message handling procedure     MOV             [WC.CLWNDPROC], OFFSET WNDPROC     MOV             [WC.CLSCBCLSEX], 0     MOV             [WC.CLSCBWNDEX], 0     MOV             EAX, [HINST]     MOV             [WC.CLSHINST], EAX ;----------Window icon     PUSH            IDI_APPLICATION     PUSH            0     CALL            LoadIconA@8     MOV             [WC.CLSHICON], EAX ;----------Window cursor     PUSH            IDC_ARROW     PUSH            0     CALL            LoadCursorA@8     MOV             [WC.CLSHCURSOR], EAX ;----------     MOV             [WC.CLBKGROUND], 17 ; Window color     MOV             DWORD PTR [WC.CLMENNAME], 0     MOV             DWORD PTR [WC.CLNAME], OFFSET CLASSNAME     PUSH            OFFSET WC     CALL            RegisterClassA@4 ; Create a window of the registered class     PUSH            0     PUSH            [HINST]     PUSH            0     PUSH            0     PUSH            400 ; DY - Window height     PUSH            400 ; DX - Window width     PUSH            100 ; Y - Coordinate of the top left corner     PUSH            100 ; X --- Coordinate of the top right corner     PUSH            WS_OVERLAPPEDWINDOW     PUSH            OFFSET TITLENAME ; Window name     PUSH            OFFSET CLASSNAME ; Class name     PUSH            0     CALL            CreateWindowExA@48 ; Check for error     CMP             EAX, 0     JZ              _ERR     MOV             [NEWHWND], EAX ; Window descriptor ;------------------------------------------     PUSH            SW_SHOWNORMAL     PUSH            [NEWHWND]     CALL            ShowWindow@8 ; Show newly-created window ;------------------------------------------     PUSH            [NEWHWND]     CALL            UpdateWindow@4 ; The command for redrawing the visible                                    ; part of the window, the WM_PAINT message ; Message-processing loop MSG_/LOOP:     PUSH            0     PUSH            0     PUSH            0     PUSH           OFFSET MSG     CALL           GetMessageA@16     CMP            EAX, 0     JE             END_LOOP     PUSH           OFFSET MSG     CALL           TranslateMessage@4     PUSH           OFFSET MSG     CALL           DispatchMessageA@4     JMP            MSG_LOOP END_LOOP: ; Exit the program (close the process)     PUSH            [MSG.MSWPARAM]     CALL            ExitProcess@4 _ERR:     JMP             END_LOOP ;------------------------------------------------------Window procedure ; Position of parameters in the stack ;  [EBP+014H] ; LPARAM ;  [EBP+10H]  ; WAPARAM ;  [EBP+0CH]  ; MES ;  [EBP+8]    ; HWND WNDPROC PROC     PUSH            EBP     MOV             EBP, ESP     PUSH            EBX     PUSH            ESI     PUSH            EDI     CMP             DWORD PTR [EBP+0CH], WM_DESTROY     JE              WMDESTROY     CMP             DWORD PTR [EBP+0CH], WM_CREATE     JE              WMCREATE     CMP             DWORD PTR [EBP+0CH], WM_COMMAND     JE              WMCOMMND     JMP             DEFWNDPROC WMCOMMND:     MOV             EAX, HWNDBTN     CMP             DWORD PTR [EBP+14H], EAX ; Hasn't the user clicked the button?     JE              WMDESTROY     MOV             EAX, 0     JMP             FINISH WMCREATE: ; Create the button window     PUSH            0     PUSH            [HINST]     PUSH            0     PUSH            DWORD PTR [EBP+08H]     PUSH            20 ; DY     PUSH            60 ; DX     PUSH            10 ; Y     PUSH            10 ; X     PUSH            STYLBTN     PUSH            OFFSET CPBUT ; Window name     PUSH            OFFSET CLSBUTN ; Window class     PUSH            0     CALL            CreateWindowExA@48     MOV             HWNDBTN, EAX ; Save the button descriptor     MOV             EAX, 0     JMP             FINISH DEFWNDPROC:     PUSH            DWORD PTR [EBP+14H]     PUSH            DWORD PTR [EBP+10H]     PUSH            DWORD PTR [EBP+0CH]     PUSH            DWORD PTR [EBP+08H]     CALL            DefWindowProcA@16     JMP             FINISH WMDESTROY:     PUSH            0  ; MB_OK     PUSH            OFFSET CAP     PUSH            OFFSET MES     PUSH            DWORD PTR [EBP+08H] ; Window descriptor     CALL            MessageBoxA@16     PUSH            0     CALL            PostQuitMessage@4 ; WM_QUIT message     MOV             EAX, 0 FINISH:     POP             EDI     POP             ESI     POP             EBX     POP             EBP     RET             16 WNDPROC  ENDP _TEXT ENDS END START 

 

^[i] Honestly, I am not proceeding properly here. After making sure that the button generated an event, you ought to determine what kind of event it was by checking the most significant word of WPARAM (the BN_CLICKED = 0 event). However, without going into particulars, I'd like to note that in most examples you consider here it is not necessary to do this for a button.