深入delphi编程理解之消息（二）发送消息函数及消息编号、消息结构体的理解

　　一、delphi发送消息的函数主要有以下三个：

　（一）、SendMessage函数，其原型如下：

function SendMessage(
  hWnd: HWND;        {目标句柄}
  Msg: UINT;         {要发送的消息(编号)}
  wParam: WPARAM;    {消息参数}
  lParam: LPARAM     {消息参数}
): LRESULT; stdcall; {返回处理结果}

　（二）、PostMessage函数

function PostMessage(
  hWnd: HWND;     {目标句柄}
  Msg: UINT;      {要发送的消息(编号)}
  wParam: WPARAM; {消息参数}
  lParam: LPARAM  {消息参数}
): BOOL; stdcall; {是否发送成功}

（三）、Perform 函数

function Perform(
  Msg: Cardinal;  {要发送的消息(编号)}
  WParam: WPARAM; {消息参数}
  LParam: LPARAM  {消息参数}
): LRESULT;       {返回处理结果}

　　SendMessage和PostMessage是API函数，Perform是delphi从TControl类开始定义的方法，所有从TControl继承的子类对象都可以使用。SendMessage和Perform方法，发送消息后，要等系统回馈结果后才执行下一步操作，而PostMessage函数则只管发送消息，发送消息后程序会马上执行下一步代码。

二、delphi 消息编号（Msg）规则及参数结构理解

（一）、消息编号

　　消息编号是window或者用户为各种不同消息定义唯一编号，他其实就是无符号整数（Cardinal）,为了便于理解， delphi以常量形式对每一个数字进行定义，主要有以下几种形式：

　　 1、windows消息，以WM_为前缀，如WM_CLOSE为窗口关闭消息；

2、delphi自定义消息，以CM_、CN为前缀；

　　3、用户自定义消息以WM_USER基数，如 Const MyMessage=WM_USER+1；

定义消息编号主要作用是定位消息处理函数，作为message关键字的识别码，例如以下函数头的定义：

 procedure WMKeyDown(var Message: TWMKeyDown); message WM_KEYDOWN;

以上函数头定义了WM_KEYDOWN消息编号，其常量数值为 WM_KEYDOWN= $0100，其作用就是当窗口接受到编号为$100的消息就执行WMKeyDown这个函数。

（二）、消息结构体

　消息结构体一般作为消息函数的参数类型出现，如上例中的TWMKeyDown就是一个消息结构体。消息结构体的标准定义如下：

PMsg = ^TMsg;
tagMSG = packed record
  hwnd: HWND;
  message: UINT;
  wParam: WPARAM;
  lParam: LPARAM;
  time: DWORD;
  pt: TPoint;
end;
TMsg = tagMSG;
MSG = tagMSG;

这种标准结构体与delphi VCL消息结构体并不兼容，所以delphi定义了自己的消息结构体。

PMessage = ^TMessage;
TMessage = packed record
  Msg: Cardinal; {消息编号}
  case Integer of
    0: (
      WParam: WPARAM;
      LParam: LPARAM;
      Result: LRESULT);
    1: (
      WParamLo: Word;
      WParamHi: Word;
      LParamLo: Word;
      LParamHi: Word;
      ResultLo: Word;
      ResultHi: Word);
end;

　　在我们实际使用中，虽然标准的结构体可以满足我们的使用，但由于使用过程中我们还要进行数据转换，为了更加便捷和易于理解，delphi在message单元文件中为我们定义大量的消息结构体，供我们直接调用。

TWMNoParams
TWMCancelMode       = TWMNoParams;
TWMChildActivate    = TWMNoParams;
TWMClear            = TWMNoParams;
TWMClose            = TWMNoParams;
TWMCopy             = TWMNoParams; TWMCut = TWMNoParams; TWMDestroy = TWMNoParams; TWMDestroyClipboard = TWMNoParams; TWMDrawClipboard = TWMNoParams; TWMFontChange = TWMNoParams; TWMGetDlgCode = TWMNoParams; TWMGetFont = TWMNoParams; TWMGetHotKey = TWMNoParams; TWMGetTextLength = TWMNoParams; TWMMDIGetActive = TWMNoParams; TWMMDIIconArrange = TWMNoParams; TWMMDIRefreshMenu = TWMNoParams; TWMNCDestroy = TWMNoParams; TWMPaintIcon = TWMNoParams; TWMPaste = TWMNoParams; TWMQueryDragIcon = TWMNoParams; TWMQueryNewPalette = TWMNoParams; TWMQueryOpen = TWMNoParams; TWMQueueSync = TWMNoParams; TWMRenderAllFormats = TWMNoParams; TWMSysColorChange = TWMNoParams; TWMTimeChange = TWMNoParams; TWMQueryUIState = TWMNoParams; TWMUndo = TWMNoParams; TWMKey TWMChar = TWMKey; TWMKeyDown = TWMKey; TWMKeyUp = TWMKey; TWMDeadChar = TWMChar; TWMSysChar = TWMKey; TWMSysKeyDown = TWMKey; TWMSysKeyUp = TWMKey; TWMMouse TWMLButtonDblClk = TWMMouse; TWMLButtonDown = TWMMouse; TWMLButtonUp = TWMMouse; TWMMButtonDblClk = TWMMouse; TWMMButtonDown = TWMMouse; TWMMButtonUp = TWMMouse; TWMMouseMove = TWMMouse; TWMRButtonDblClk = TWMMouse; TWMRButtonDown = TWMMouse; TWMRButtonUp = TWMMouse; TWMMouseWheel TMSHMouseWheel TWMWindowPosMsg TWMWindowPosChanged = TWMWindowPosMsg; TWMWindowPosChanging = TWMWindowPosMsg; TWMScroll TWMHScroll = TWMScroll; TWMVScroll = TWMScroll; TWMActivate TWMActivateApp TWMAskCBFormatName TWMChangeCBChain TWMCharToItem TWMVKeyToItem = TWMCharToItem; TWMChooseFont_GetLogFont TWMCommand TWMCompacting TWMCompareItem TWMCopyData TWMCreate TWMCtlColor TWMCtlColorBtn = TWMCtlColor; TWMCtlColorDlg = TWMCtlColor; TWMCtlColorEdit = TWMCtlColor; TWMCtlColorListbox = TWMCtlColor; TWMCtlColorMsgbox = TWMCtlColor; TWMCtlColorScrollbar = TWMCtlColor; TWMCtlColorStatic = TWMCtlColor; TWMDDE_Ack TWMDDE_Advise TWMDDE_Data TWMDDE_Execute TWMDDE_Initiate TWMDDE_Poke TWMDDE_Request TWMDDE_Terminate TWMDDE_Unadvise TWMDeleteItem TWMDevModeChange TWMDrawItem TWMDropFiles TWMEnable TWMEndSession TWMEnterIdle TWMEnterMenuLoop TWMExitMenuLoop = TWMEnterMenuLoop; TWMEraseBkgnd TWMGetIcon TWMGetMinMaxInfo TWMGetText TWMHotKey TWMHScrollClipboard TWMIconEraseBkgnd = TWMEraseBkgnd; TWMInitDialog TWMInitMenu TWMInitMenuPopup TWMKillFocus TWMMDIActivate TWMMDICascade TWMMDICreate TWMMDIDestroy TWMMDIMaximize TWMMDINext TWMMDIRestore TWMMDISetMenu TWMMDITile TWMMeasureItem TWMMenuChar TWMMenuSelect TWMMouseActivate TWMMove TWMMoving TWMNCActivate TWMNCCalcSize TWMNCCreate TWMNCHitTest TWMNCHitMessage TWMNCLButtonDblClk = TWMNCHitMessage; TWMNCLButtonDown = TWMNCHitMessage; TWMNCLButtonUp = TWMNCHitMessage; TWMNCMButtonDblClk = TWMNCHitMessage; TWMNCMButtonDown = TWMNCHitMessage; TWMNCMButtonUp = TWMNCHitMessage; TWMNCMouseMove = TWMNCHitMessage; TWMNCRButtonDblClk = TWMNCHitMessage; TWMNCRButtonDown = TWMNCHitMessage; TWMNCRButtonUp = TWMNCHitMessage; TWMNCPaint TWMNextDlgCtl TWMNotify TWMNotifyFormat TWMPaint TWMPaintClipboard TWMPaletteChanged TWMPaletteIsChanging TWMParentNotify TWMPower TWMQueryEndSession TWMQuit TWMRenderFormat TWMSetCursor TWMSetFocus TWMSetFont TWMSetHotKey TWMSetIcon TWMSetRedraw TWMSetText TWMShowWindow TWMSize TWMSizeClipboard TWMSpoolerStatus TWMStyleChange TWMStyleChanged = TWMStyleChange; TWMStyleChanging = TWMStyleChange; TWMSysCommand TWMSysDeadChar TWMSystemError TWMTimer TWMUIState TWMChangeUIState = TWMUIState; TWMUpdateUIState = TWMUIState; TWMVScrollClipboard TWMWinIniChange TWMSettingChange TWMHelp TWMDisplayChange TWMContextMenu TWMPrint TWMPrintClient = TWMPrint;

深入delphi编程理解之消息（二）发送消息函数及消息编号、消息结构体的理解

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