PostMessage(m_hVLWin, WM_KEYDOWN, VK_DOWN, 0x00500001)

PostMessage(m_hVLWin, WM_KEYDOWN, VK_DOWN, 0x00500001)
giải thích:  
- PostMessage sẽ truyền message
 m_hVLWin: handle của window.
WM_KEYDOWN : gửi phím đến window
 VK_DOWN: cái này là virtual key code:

Constant/value	Description
VK_LBUTTON 0x01	Left mouse button
VK_RBUTTON 0x02	Right mouse button
VK_CANCEL 0x03	Control-break processing
VK_MBUTTON 0x04	Middle mouse button (three-button mouse)
VK_XBUTTON1 0x05	X1 mouse button
VK_XBUTTON2 0x06	X2 mouse button
- 0x07	Undefined
VK_BACK 0x08	BACKSPACE key
VK_TAB 0x09	TAB key
- 0x0A-0B	Reserved
VK_CLEAR 0x0C	CLEAR key
VK_RETURN 0x0D	ENTER key
- 0x0E-0F	Undefined
VK_SHIFT 0x10	SHIFT key
VK_CONTROL 0x11	CTRL key
VK_MENU 0x12	ALT key
VK_PAUSE 0x13	PAUSE key
VK_CAPITAL 0x14	CAPS LOCK key
VK_KANA 0x15	IME Kana mode
VK_HANGUEL 0x15	IME Hanguel mode (maintained for compatibility; use VK_HANGUL)
VK_HANGUL 0x15	IME Hangul mode
- 0x16	Undefined
VK_JUNJA 0x17	IME Junja mode
VK_FINAL 0x18	IME final mode
VK_HANJA 0x19	IME Hanja mode
VK_KANJI 0x19	IME Kanji mode
- 0x1A	Undefined
VK_ESCAPE 0x1B	ESC key
VK_CONVERT 0x1C	IME convert
VK_NONCONVERT 0x1D	IME nonconvert
VK_ACCEPT 0x1E	IME accept
VK_MODECHANGE 0x1F	IME mode change request
VK_SPACE 0x20	SPACEBAR
VK_PRIOR 0x21	PAGE UP key
VK_NEXT 0x22	PAGE DOWN key
VK_END 0x23	END key
VK_HOME 0x24	HOME key
VK_LEFT 0x25	LEFT ARROW key
VK_UP 0x26	UP ARROW key
VK_RIGHT 0x27	RIGHT ARROW key
VK_DOWN 0x28	DOWN ARROW key
VK_SELECT 0x29	SELECT key
VK_PRINT 0x2A	PRINT key
VK_EXECUTE 0x2B	EXECUTE key
VK_SNAPSHOT 0x2C	PRINT SCREEN key
VK_INSERT 0x2D	INS key
VK_DELETE 0x2E	DEL key
VK_HELP 0x2F	HELP key
0x30	0 key
0x31	1 key
0x32	2 key
0x33	3 key
0x34	4 key
0x35	5 key
0x36	6 key
0x37	7 key
0x38	8 key
0x39	9 key
- 0x3A-40	Undefined
0x41	A key
0x42	B key
0x43	C key
0x44	D key
0x45	E key
0x46	F key
0x47	G key
0x48	H key
0x49	I key
0x4A	J key
0x4B	K key
0x4C	L key
0x4D	M key
0x4E	N key
0x4F	O key
0x50	P key
0x51	Q key
0x52	R key
0x53	S key
0x54	T key
0x55	U key
0x56	V key
0x57	W key
0x58	X key
0x59	Y key
0x5A	Z key
VK_LWIN 0x5B	Left Windows key (Natural keyboard)
VK_RWIN 0x5C	Right Windows key (Natural keyboard)
VK_APPS 0x5D	Applications key (Natural keyboard)
- 0x5E	Reserved
VK_SLEEP 0x5F	Computer Sleep key
VK_NUMPAD0 0x60	Numeric keypad 0 key
VK_NUMPAD1 0x61	Numeric keypad 1 key
VK_NUMPAD2 0x62	Numeric keypad 2 key
VK_NUMPAD3 0x63	Numeric keypad 3 key
VK_NUMPAD4 0x64	Numeric keypad 4 key
VK_NUMPAD5 0x65	Numeric keypad 5 key
VK_NUMPAD6 0x66	Numeric keypad 6 key
VK_NUMPAD7 0x67	Numeric keypad 7 key
VK_NUMPAD8 0x68	Numeric keypad 8 key
VK_NUMPAD9 0x69	Numeric keypad 9 key
VK_MULTIPLY 0x6A	Multiply key
VK_ADD 0x6B	Add key
VK_SEPARATOR 0x6C	Separator key
VK_SUBTRACT 0x6D	Subtract key
VK_DECIMAL 0x6E	Decimal key
VK_DIVIDE 0x6F	Divide key
VK_F1 0x70	F1 key
VK_F2 0x71	F2 key
VK_F3 0x72	F3 key
VK_F4 0x73	F4 key
VK_F5 0x74	F5 key
VK_F6 0x75	F6 key
VK_F7 0x76	F7 key
VK_F8 0x77	F8 key
VK_F9 0x78	F9 key
VK_F10 0x79	F10 key
VK_F11 0x7A	F11 key
VK_F12 0x7B	F12 key
VK_F13 0x7C	F13 key
VK_F14 0x7D	F14 key
VK_F15 0x7E	F15 key
VK_F16 0x7F	F16 key
VK_F17 0x80	F17 key
VK_F18 0x81	F18 key
VK_F19 0x82	F19 key
VK_F20 0x83	F20 key
VK_F21 0x84	F21 key
VK_F22 0x85	F22 key
VK_F23 0x86	F23 key
VK_F24 0x87	F24 key
- 0x88-8F	Unassigned
VK_NUMLOCK 0x90	NUM LOCK key
VK_SCROLL 0x91	SCROLL LOCK key
0x92-96	OEM specific
- 0x97-9F	Unassigned
VK_LSHIFT 0xA0	Left SHIFT key
VK_RSHIFT 0xA1	Right SHIFT key
VK_LCONTROL 0xA2	Left CONTROL key
VK_RCONTROL 0xA3	Right CONTROL key
VK_LMENU 0xA4	Left MENU key
VK_RMENU 0xA5	Right MENU key
VK_BROWSER_BACK 0xA6	Browser Back key
VK_BROWSER_FORWARD 0xA7	Browser Forward key
VK_BROWSER_REFRESH 0xA8	Browser Refresh key
VK_BROWSER_STOP 0xA9	Browser Stop key
VK_BROWSER_SEARCH 0xAA	Browser Search key
VK_BROWSER_FAVORITES 0xAB	Browser Favorites key
VK_BROWSER_HOME 0xAC	Browser Start and Home key
VK_VOLUME_MUTE 0xAD	Volume Mute key
VK_VOLUME_DOWN 0xAE	Volume Down key
VK_VOLUME_UP 0xAF	Volume Up key
VK_MEDIA_NEXT_TRACK 0xB0	Next Track key
VK_MEDIA_PREV_TRACK 0xB1	Previous Track key
VK_MEDIA_STOP 0xB2	Stop Media key
VK_MEDIA_PLAY_PAUSE 0xB3	Play/Pause Media key
VK_LAUNCH_MAIL 0xB4	Start Mail key
VK_LAUNCH_MEDIA_SELECT 0xB5	Select Media key
VK_LAUNCH_APP1 0xB6	Start Application 1 key
VK_LAUNCH_APP2 0xB7	Start Application 2 key
- 0xB8-B9	Reserved
VK_OEM_1 0xBA	Used for miscellaneous characters; it can vary by keyboard. For the US standard keyboard, the ';:' key
VK_OEM_PLUS 0xBB	For any country/region, the '+' key
VK_OEM_COMMA 0xBC	For any country/region, the ',' key
VK_OEM_MINUS 0xBD	For any country/region, the '-' key
VK_OEM_PERIOD 0xBE	For any country/region, the '.' key
VK_OEM_2 0xBF	Used for miscellaneous characters; it can vary by keyboard. For the US standard keyboard, the '/?' key
VK_OEM_3 0xC0	Used for miscellaneous characters; it can vary by keyboard. For the US standard keyboard, the '`~' key
- 0xC1-D7	Reserved
- 0xD8-DA	Unassigned
VK_OEM_4 0xDB	Used for miscellaneous characters; it can vary by keyboard. For the US standard keyboard, the '[{' key
VK_OEM_5 0xDC	Used for miscellaneous characters; it can vary by keyboard. For the US standard keyboard, the '\|' key
VK_OEM_6 0xDD	Used for miscellaneous characters; it can vary by keyboard. For the US standard keyboard, the ']}' key
VK_OEM_7 0xDE	Used for miscellaneous characters; it can vary by keyboard. For the US standard keyboard, the 'single-quote/double-quote' key
VK_OEM_8 0xDF	Used for miscellaneous characters; it can vary by keyboard.
- 0xE0	Reserved
0xE1	OEM specific
VK_OEM_102 0xE2	Either the angle bracket key or the backslash key on the RT 102-key keyboard
0xE3-E4	OEM specific
VK_PROCESSKEY 0xE5	IME PROCESS key
0xE6	OEM specific
VK_PACKET 0xE7	Used to pass Unicode characters as if they were keystrokes. The VK_PACKET key is the low word of a 32-bit Virtual Key value used for non-keyboard input methods. For more information, see Remark in KEYBDINPUT, SendInput, WM_KEYDOWN, and WM_KEYUP
- 0xE8	Unassigned
0xE9-F5	OEM specific
VK_ATTN 0xF6	Attn key
VK_CRSEL 0xF7	CrSel key
VK_EXSEL 0xF8	ExSel key
VK_EREOF 0xF9	Erase EOF key
VK_PLAY 0xFA	Play key
VK_ZOOM 0xFB	Zoom key
VK_NONAME 0xFC	Reserved
VK_PA1 0xFD	PA1 key
VK_OEM_CLEAR 0xFE	Clear key