Sends the specified message to a window or windows.
It uses P/Invoke that allows you to access structs, callbacks, and functions in unmanaged libraries from your managed code.
## SendMessage function
The SendMessage function calls the window procedure for the specified window and does not return until the window procedure has processed the message.
```cs
SendMessage (int hwnd, int wMsg, int wParam, int lParam);
```
### Parameters
#### hWnd
Type: HWND
> A handle to the window whose window procedure will receive the message. If this parameter is HWND_BROADCAST ((HWND)0xffff), the message is sent to all top-level windows in the system, including disabled or invisible unowned windows, overlapped windows, and pop-up windows; but the message is not sent to child windows.
Message sending is subject to UIPI. The thread of a process can send messages only to message queues of threads in processes of lesser or equal integrity level.
#### Msg
Type: UINT
> The message to be sent.
For lists of the system-provided messages, see System-Defined Messages.
#### wParam
Type: WPARAM
> Additional message-specific information.
#### lParam
Type: LPARAM
> Additional message-specific information.
Here is the implementation of it using C# with PInvoke
```cs
//Send Message API Class
//send Message Win32 Ap interop
using System.Runtime.InteropServices;
namespace KillerCodes.win32.API
{
public static class WIN32_API
{
[DllImport("user32.dll", EntryPoint="SendMessageW")]
private static extern int SendMessage (int hwnd, int wMsg, int wParam, int lParam);
[DllImport("user32.dll", EntryPoint = "SendMessageW")]
private static extern int SendMessageFL(int hwnd, int wMsg, int wParam, string lParam);
[DllImport("user32.dll", EntryPoint = "SendMessageW")]
private static extern int SendMessageSD(int hwnd, int wMsg, string wParam, int lParam);
public enum WM : int
{
WM_ACTIVATE = 0x6,
WM_ACTIVATEAPP = 0x1C,
WM_ADSPROP_NOTIFY_APPLY = (WM_USER + 1104),
WM_USER = 0x400,
WM_ADSPROP_NOTIFY_CHANGE = (WM_USER + 1103),
WM_ADSPROP_NOTIFY_EXIT = (WM_USER + 1107),
WM_ADSPROP_NOTIFY_FOREGROUND = (WM_USER + 1106),
WM_ADSPROP_NOTIFY_PAGEHWND = (WM_USER + 1102),
WM_ADSPROP_NOTIFY_PAGEINIT = (WM_USER + 1101),
WM_ADSPROP_NOTIFY_SETFOCUS = (WM_USER + 1105),
WM_ADSPROP_NOTIFY_SHOW_ERROR_DIALOG = (WM_USER + 1111),
WM_AFXFIRST = 0x360,
WM_AFXLAST = 0x37F,
WM_APP = 0x8000,
WM_APPCOMMAND = 0x319,
WM_ASKCBFORMATNAME = 0x30C,
WM_CANCELJOURNAL = 0x4B,
WM_CANCELMODE = 0x1F,
WM_CAP_ABORT = (WM_CAP_START+ 69),
WM_CAP_START = WM_USER,
WM_CAP_DLG_VIDEOCOMPRESSION = (WM_CAP_START+ 46),
WM_CAP_DLG_VIDEODISPLAY = (WM_CAP_START+ 43),
WM_CAP_DLG_VIDEOFORMAT = (WM_CAP_START+ 41),
WM_CAP_DLG_VIDEOSOURCE = (WM_CAP_START+ 42),
WM_CAP_DRIVER_CONNECT = (WM_CAP_START+ 10),
WM_CAP_DRIVER_DISCONNECT = (WM_CAP_START+ 11),
WM_CAP_DRIVER_GET_CAPS = (WM_CAP_START+ 14),
WM_CAP_DRIVER_GET_NAMEA = (WM_CAP_START+ 12),
WM_CAP_DRIVER_GET_NAMEW = (WM_CAP_UNICODE_START+ 12),
WM_CAP_UNICODE_START = WM_USER+100,
WM_CAP_DRIVER_GET_VERSIONA = (WM_CAP_START+ 13),
WM_CAP_DRIVER_GET_VERSIONW = (WM_CAP_UNICODE_START+ 13),
WM_CAP_EDIT_COPY = (WM_CAP_START+ 30),
WM_CAP_END = WM_CAP_UNICODE_END,
WM_CAP_UNICODE_END = WM_CAP_PAL_SAVEW,
WM_CAP_FILE_ALLOCATE = (WM_CAP_START+ 22),
WM_CAP_FILE_GET_CAPTURE_FILEA = (WM_CAP_START+ 21),
WM_CAP_FILE_GET_CAPTURE_FILEW = (WM_CAP_UNICODE_START+ 21),
WM_CAP_FILE_SAVEASA = (WM_CAP_START+ 23),
WM_CAP_FILE_SAVEASW = (WM_CAP_UNICODE_START+ 23),
WM_CAP_FILE_SAVEDIBA = (WM_CAP_START+ 25),
WM_CAP_FILE_SAVEDIBW = (WM_CAP_UNICODE_START+ 25),
WM_CAP_FILE_SET_CAPTURE_FILEA = (WM_CAP_START+ 20),
WM_CAP_FILE_SET_CAPTURE_FILEW = (WM_CAP_UNICODE_START+ 20),
WM_CAP_FILE_SET_INFOCHUNK = (WM_CAP_START+ 24),
WM_CAP_GET_AUDIOFORMAT = (WM_CAP_START+ 36),
WM_CAP_GET_CAPSTREAMPTR = (WM_CAP_START+ 1),
WM_CAP_GET_MCI_DEVICEA = (WM_CAP_START+ 67),
WM_CAP_GET_MCI_DEVICEW = (WM_CAP_UNICODE_START+ 67),
WM_CAP_GET_SEQUENCE_SETUP = (WM_CAP_START+ 65),
WM_CAP_GET_STATUS = (WM_CAP_START+ 54),
WM_CAP_GET_USER_DATA = (WM_CAP_START+ 8),
WM_CAP_GET_VIDEOFORMAT = (WM_CAP_START+ 44),
WM_CAP_GRAB_FRAME = (WM_CAP_START+ 60),
WM_CAP_GRAB_FRAME_NOSTOP = (WM_CAP_START+ 61),
WM_CAP_PAL_AUTOCREATE = (WM_CAP_START+ 83),
WM_CAP_PAL_MANUALCREATE = (WM_CAP_START+ 84),
WM_CAP_PAL_OPENA = (WM_CAP_START+ 80),
WM_CAP_PAL_OPENW = (WM_CAP_UNICODE_START+ 80),
WM_CAP_PAL_PASTE = (WM_CAP_START+ 82),
WM_CAP_PAL_SAVEA = (WM_CAP_START+ 81),
WM_CAP_PAL_SAVEW = (WM_CAP_UNICODE_START+ 81),
WM_CAP_SEQUENCE = (WM_CAP_START+ 62),
WM_CAP_SEQUENCE_NOFILE = (WM_CAP_START+ 63),
WM_CAP_SET_AUDIOFORMAT = (WM_CAP_START+ 35),
WM_CAP_SET_CALLBACK_CAPCONTROL = (WM_CAP_START+ 85),
WM_CAP_SET_CALLBACK_ERRORA = (WM_CAP_START+ 2),
WM_CAP_SET_CALLBACK_ERRORW = (WM_CAP_UNICODE_START+ 2),
WM_CAP_SET_CALLBACK_FRAME = (WM_CAP_START+ 5),
WM_CAP_SET_CALLBACK_STATUSA = (WM_CAP_START+ 3),
WM_CAP_SET_CALLBACK_STATUSW = (WM_CAP_UNICODE_START+ 3),
WM_CAP_SET_CALLBACK_VIDEOSTREAM = (WM_CAP_START+ 6),
WM_CAP_SET_CALLBACK_WAVESTREAM = (WM_CAP_START+ 7),
WM_CAP_SET_CALLBACK_YIELD = (WM_CAP_START+ 4),
WM_CAP_SET_MCI_DEVICEA = (WM_CAP_START+ 66),
WM_CAP_SET_MCI_DEVICEW = (WM_CAP_UNICODE_START+ 66),
WM_CAP_SET_OVERLAY = (WM_CAP_START+ 51),
WM_CAP_SET_PREVIEW = (WM_CAP_START+ 50),
WM_CAP_SET_PREVIEWRATE = (WM_CAP_START+ 52),
WM_CAP_SET_SCALE = (WM_CAP_START+ 53),
WM_CAP_SET_SCROLL = (WM_CAP_START+ 55),
WM_CAP_SET_SEQUENCE_SETUP = (WM_CAP_START+ 64),
WM_CAP_SET_USER_DATA = (WM_CAP_START+ 9),
WM_CAP_SET_VIDEOFORMAT = (WM_CAP_START+ 45),
WM_CAP_SINGLE_FRAME = (WM_CAP_START+ 72),
WM_CAP_SINGLE_FRAME_CLOSE = (WM_CAP_START+ 71),
WM_CAP_SINGLE_FRAME_OPEN = (WM_CAP_START+ 70),
WM_CAP_STOP = (WM_CAP_START+ 68),
WM_CAPTURECHANGED = 0x215,
WM_CHANGECBCHAIN = 0x30D,
WM_CHANGEUISTATE = 0x127,
WM_CHAR = 0x102,
WM_CHARTOITEM = 0x2F,
WM_CHOOSEFONT_GETLOGFONT = (WM_USER + 1),
WM_CHOOSEFONT_SETFLAGS = (WM_USER + 102),
WM_CHOOSEFONT_SETLOGFONT = (WM_USER + 101),
WM_CLEAR = 0x303,
WM_CLOSE = 0x10,
WM_COMMAND = 0x111,
WM_COMMNOTIFY = 0x44,
WM_COMPACTING = 0x41,
WM_COMPAREITEM = 0x39,
WM_CONTEXTMENU = 0x7B,
WM_CONVERTREQUEST = 0x10A,
WM_CONVERTREQUESTEX = 0x108,
WM_CONVERTRESULT = 0x10B,
WM_COPY = 0x301,
WM_COPYDATA = 0x4A,
WM_CPL_LAUNCH = (WM_USER+1000),
WM_CPL_LAUNCHED = (WM_USER+1001),
WM_CREATE = 0x1,
WM_CTLCOLOR = 0x19,
WM_CTLCOLORBTN = 0x135,
WM_CTLCOLORDLG = 0x136,
WM_CTLCOLOREDIT = 0x133,
WM_CTLCOLORLISTBOX = 0x134,
WM_CTLCOLORMSGBOX = 0x132,
WM_CTLCOLORSCROLLBAR = 0x137,
WM_CTLCOLORSTATIC = 0x138,
WM_CUT = 0x300,
WM_DDE_FIRST = 0x3E0,
WM_DDE_ACK = (WM_DDE_FIRST + 4),
WM_DDE_ADVISE = (WM_DDE_FIRST + 2),
WM_DDE_DATA = (WM_DDE_FIRST + 5),
WM_DDE_EXECUTE = (WM_DDE_FIRST + 8),
WM_DDE_INITIATE = (WM_DDE_FIRST),
WM_DDE_LAST = (WM_DDE_FIRST + 8),
WM_DDE_POKE = (WM_DDE_FIRST + 7),
WM_DDE_REQUEST = (WM_DDE_FIRST + 6),
WM_DDE_TERMINATE = (WM_DDE_FIRST + 1),
WM_DDE_UNADVISE = (WM_DDE_FIRST + 3),
WM_DEADCHAR = 0x103,
WM_DELETEITEM = 0x2D,
WM_DESTROY = 0x2,
WM_DESTROYCLIPBOARD = 0x307,
WM_DEVICECHANGE = 0x219,
WM_DEVMODECHANGE = 0x1B,
WM_DISPLAYCHANGE = 0x7E,
WM_DRAWCLIPBOARD = 0x308,
WM_DRAWITEM = 0x2B,
WM_DROPFILES = 0x233,
WM_ENABLE = 0xA,
WM_ENDSESSION = 0x16,
WM_ENTERIDLE = 0x121,
WM_ENTERMENULOOP = 0x211,
WM_ENTERSIZEMOVE = 0x231,
WM_ERASEBKGND = 0x14,
WM_EXITMENULOOP = 0x212,
WM_EXITSIZEMOVE = 0x232,
WM_FONTCHANGE = 0x1D,
WM_FORWARDMSG = 0x37F,
WM_GETDLGCODE = 0x87,
WM_GETFONT = 0x31,
WM_GETHOTKEY = 0x33,
WM_GETICON = 0x7F,
WM_GETMINMAXINFO = 0x24,
WM_GETOBJECT = 0x3D,
WM_GETTEXT = 0xD,
WM_GETTEXTLENGTH = 0xE,
WM_HANDHELDFIRST = 0x358,
WM_HANDHELDLAST = 0x35F,
WM_HELP = 0x53,
WM_HOTKEY = 0x312,
WM_HSCROLL = 0x114,
WM_HSCROLLCLIPBOARD = 0x30E,
WM_ICONERASEBKGND = 0x27,
WM_IME_CHAR = 0x286,
WM_IME_COMPOSITION = 0x10F,
WM_IME_COMPOSITIONFULL = 0x284,
WM_IME_CONTROL = 0x283,
WM_IME_ENDCOMPOSITION = 0x10E,
WM_IME_KEYDOWN = 0x290,
WM_IME_KEYLAST = 0x10F,
WM_IME_KEYUP = 0x291,
WM_IME_NOTIFY = 0x282,
WM_IME_REPORT = 0x280,
WM_IME_REQUEST = 0x288,
WM_IME_SELECT = 0x285,
WM_IME_SETCONTEXT = 0x281,
WM_IME_STARTCOMPOSITION = 0x10D,
WM_IMEKEYDOWN = 0x290,
WM_IMEKEYUP = 0x291,
WM_INITDIALOG = 0x110,
WM_INITMENU = 0x116,
WM_INITMENUPOPUP = 0x117,
WM_INPUTLANGCHANGE = 0x51,
WM_INPUTLANGCHANGEREQUEST = 0x50,
WM_INTERIM = 0x10C,
WM_KEYDOWN = 0x100,
WM_KEYFIRST = 0x100,
WM_KEYLAST = 0x108,
WM_KEYUP = 0x101,
WM_KILLFOCUS = 0x8,
WM_LBUTTONDBLCLK = 0x203,
WM_LBUTTONDOWN = 0x201,
WM_LBUTTONUP = 0x202,
WM_MBUTTONDBLCLK = 0x209,
WM_MBUTTONDOWN = 0x207,
WM_MBUTTONUP = 0x208,
WM_MDIACTIVATE = 0x222,
WM_MDICASCADE = 0x227,
WM_MDICREATE = 0x220,
WM_MDIDESTROY = 0x221,
WM_MDIGETACTIVE = 0x229,
WM_MDIICONARRANGE = 0x228,
WM_MDIMAXIMIZE = 0x225,
WM_MDINEXT = 0x224,
WM_MDIREFRESHMENU = 0x234,
WM_MDIRESTORE = 0x223,
WM_MDISETMENU = 0x230,
WM_MDITILE = 0x226,
WM_MEASUREITEM = 0x2C,
WM_MENUCHAR = 0x120,
WM_MENUCOMMAND = 0x126,
WM_MENUDRAG = 0x123,
WM_MENUGETOBJECT = 0x124,
WM_MENURBUTTONUP = 0x122,
WM_MENUSELECT = 0x11F,
WM_MOUSEACTIVATE = 0x21,
WM_MOUSEFIRST = 0x200,
WM_MOUSEHOVER = 0x2A1,
WM_MOUSELAST = 0x209,
WM_MOUSELEAVE = 0x2A3,
WM_MOUSEMOVE = 0x200,
WM_MOUSEWHEEL = 0x20A,
WM_MOVE = 0x3,
WM_MOVING = 0x216,
WM_NCACTIVATE = 0x86,
WM_NCCALCSIZE = 0x83,
WM_NCCREATE = 0x81,
WM_NCDESTROY = 0x82,
WM_NCHITTEST = 0x84,
WM_NCLBUTTONDBLCLK = 0xA3,
WM_NCLBUTTONDOWN = 0xA1,
WM_NCLBUTTONUP = 0xA2,
WM_NCMBUTTONDBLCLK = 0xA9,
WM_NCMBUTTONDOWN = 0xA7,
WM_NCMBUTTONUP = 0xA8,
WM_NCMOUSEHOVER = 0x2A0,
WM_NCMOUSELEAVE = 0x2A2,
WM_NCMOUSEMOVE = 0xA0,
WM_NCPAINT = 0x85,
WM_NCRBUTTONDBLCLK = 0xA6,
WM_NCRBUTTONDOWN = 0xA4,
WM_NCRBUTTONUP = 0xA5,
WM_NCXBUTTONDOWN = 0xAB,
WM_NCXBUTTONUP = 0xAC,
WM_NEXTDLGCTL = 0x28,
WM_NEXTMENU = 0x213,
WM_NOTIFY = 0x4E,
WM_NOTIFYFORMAT = 0x55,
WM_NULL = 0x0,
WM_OTHERWINDOWCREATED = 0x42,
WM_OTHERWINDOWDESTROYED = 0x43,
WM_PAINT = 0xF,
WM_PAINTCLIPBOARD = 0x309,
WM_PAINTICON = 0x26,
WM_PALETTECHANGED = 0x311,
WM_PALETTEISCHANGING = 0x310,
WM_PARENTNOTIFY = 0x210,
WM_PASTE = 0x302,
WM_PENWINFIRST = 0x380,
WM_PENWINLAST = 0x38F,
WM_POWER = 0x48,
WM_POWERBROADCAST = 0x218,
WM_PRINT = 0x317,
WM_PRINTCLIENT = 0x318,
WM_PSD_ENVSTAMPRECT = (WM_USER + 5),
WM_PSD_FULLPAGERECT = (WM_USER + 1),
WM_PSD_GREEKTEXTRECT = (WM_USER + 4),
WM_PSD_MARGINRECT = (WM_USER + 3),
WM_PSD_MINMARGINRECT = (WM_USER + 2),
WM_PSD_PAGESETUPDLG = (WM_USER),
WM_PSD_YAFULLPAGERECT = (WM_USER + 6),
WM_QUERYDRAGICON = 0x37,
WM_QUERYENDSESSION = 0x11,
WM_QUERYNEWPALETTE = 0x30F,
WM_QUERYOPEN = 0x13,
WM_QUERYUISTATE = 0x129,
WM_QUEUESYNC = 0x23,
WM_QUIT = 0x12,
WM_RASDIALEVENT = 0xCCCD,
WM_RBUTTONDBLCLK = 0x206,
WM_RBUTTONDOWN = 0x204,
WM_RBUTTONUP = 0x205,
WM_RENDERALLFORMATS = 0x306,
WM_RENDERFORMAT = 0x305,
WM_SETCURSOR = 0x20,
WM_SETFOCUS = 0x7,
WM_SETFONT = 0x30,
WM_SETHOTKEY = 0x32,
WM_SETICON = 0x80,
WM_SETREDRAW = 0xB,
WM_SETTEXT = 0xC,
WM_SETTINGCHANGE = WM_WININICHANGE,
WM_SHOWWINDOW = 0x18,
WM_SIZE = 0x5,
WM_SIZECLIPBOARD = 0x30B,
WM_SIZING = 0x214,
WM_SPOOLERSTATUS = 0x2A,
WM_STYLECHANGED = 0x7D,
WM_STYLECHANGING = 0x7C,
WM_SYNCPAINT = 0x88,
WM_SYSCHAR = 0x106,
WM_SYSCOLORCHANGE = 0x15,
WM_SYSCOMMAND = 0x112,
WM_SYSDEADCHAR = 0x107,
WM_SYSKEYDOWN = 0x104,
WM_SYSKEYUP = 0x105,
WM_TCARD = 0x52,
WM_TIMECHANGE = 0x1E,
WM_TIMER = 0x113,
WM_UNDO = 0x304,
WM_UNINITMENUPOPUP = 0x125,
WM_UPDATEUISTATE = 0x128,
WM_USERCHANGED = 0x54,
WM_VKEYTOITEM = 0x2E,
WM_VSCROLL = 0x115,
WM_VSCROLLCLIPBOARD = 0x30A,
WM_WINDOWPOSCHANGED = 0x47,
WM_WINDOWPOSCHANGING = 0x46,
WM_WININICHANGE = 0x1A,
WM_WNT_CONVERTREQUESTEX = 0x109,
WM_XBUTTONDBLCLK = 0x20D,
WM_XBUTTONDOWN = 0x20B,
WM_XBUTTONUP = 0x20C
}
public static int WIN32_SendMessage( int handle, WM ww,int WParam, int LParam)
{
int wm = (int)ww;
int ret = SendMessage(handle, wm,WParam, LParam);
return ret;
}
}
}
```