在平時寫程序時,總是碰到窗體（TForm）與線程（TThread）消息通信問題。令人煩惱的是窗體不能向線程（TThread）發送消息（線程沒有窗口句柄）。經過幾天的折騰，想出二種解決方案，拿出來跟大家探討探討。

第一。我們知道VC++ 中的MFC類庫是自已封裝了消息處理（BEGINMESSAGE, ENDMESSAGE），在MFC中對消息的處理是通過建立一張消息映射表，而把方法（function）或過程（PRocedure）的地址保存到映射表里（消息處理實質上是方法或過程的調用）,再加上一個消息分發機制，來實現消息的接收發送 <詳見VC++技術內幕>。所以我們只要為線程里建立一張消息映射表，并建立相應的消息分發機制。這樣就可以處理窗體發送到線程的消息。以下代碼是實現消息映射表和消息分發的類（詳見 <../消息處理設計(線程)1/MessageHandle.pas> 中 ）

unit MessageHandle;

interface

uses messages,Classes,SysUtils,Dialogs;

const PMSG_BASE = $BE00;   //自定義消息基址;

      PMSG_NUM = 200;      //消息表大小；

{**自定義消息處理類

  *;功能 = 建立自定義消息表，處理線程之間

  *   以及與主窗體之間的自定義消息(宏觀)

*}

  //消息處理句柄

  TMessageHandle = procedure(var Message: TMessage) of Object;

  TPDispatcher = class(TObject)

  private

    //消息對應表(消息ID為數組下標);

    MessageHandles: array of TMessageHandle;

    //從消息ID得到數組ID

    function GetIndexFromMsgID(const aMessageID: cardinal): Integer;

  public

    constructor Create;

    destructor Destroy;

    //發送消息

    procedure SendMessage(var Message: TMessage); overload;

    //添加自定義消息到消息對應表;

    procedure AddHandle(const aMessageID: cardinal; aMessageHandle: TMessageHandle);

  end;

  //

implementation

{ TPDispatcher }

constructor TPDispatcher.Create;

var i: Integer;

begin

  SetLength(MessageHandles,PMSG_NUM);  //200個消息的消息對應表

  //初始化消息隊列;

  for i := 0 to Pred(PMSG_NUM) do

    MessageHandles[i] := nil;

end;

destructor TPDispatcher.Destroy;

begin

   {釋放消息對應表}

  FreeAndNil(MessageHandles);

end;

procedure TPDispatcher.AddHandle(const aMessageID: cardinal;

  aMessageHandle: TMessageHandle);

var tID: Integer;

begin

  tID := GetIndexFromMsgID(aMessageID);

  Assert((tID > 0) or (tID < Pred(PMSG_NUM)) );

  Assert(Assigned(aMessageHandle));

  MessageHandles[tID] := aMessageHandle;

end;

function TPDispatcher.GetIndexFromMsgID(const aMessageID: cardinal): Integer;

begin

  Result := aMessageID - PMSG_BASE;

end;

procedure TPDispatcher.SendMessage(var Message: TMessage);

var tID: Integer;

    tMsgHandle: TMessageHandle;

begin

  tID := GetIndexFromMsgID(Message.Msg);

  Assert((tID > 0) or (tID < Pred(PMSG_NUM)));

  tMsgHandle := MessageHandles[tID];

  if Assigned(tMsgHandle) then

    tMsgHandle(Message);

end;

現在我們只需要注冊一下自定義的消息，然后通過消息分發類（TPDispatcher），實現對線程消息的處理。代碼如下<詳見../消息處理設計(線程)1/test/unit1.pas>：

Unit unit1

const

      {自定久線程消息}

      MY_MESSAGE2 = PMSG_BASE + 02; 

type

  TForm1 = class(TForm)

    AddMsgList: TButton;

    SendThead: TButton;

    sendForm: TButton;

    sendOther: TButton;

    procedure SendTheadClick(Sender: TObject);  //發送消息

    procedure FormCreate(Sender: TObject);

    procedure FormDestroy(Sender: TObject);

  private

    Fdispatcher: TPDispatcher;  消息映射表類

    Fhandle: TPHandler;

    FThread:  TPTHread;  自定義線程類

  public

    { Public declarations }

  end;

var

  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.SendTheadClick(Sender: TObject);

var aMessage: TMessage;begin

    aMessage.Msg := MY_MESSAGE2;

    aMessage.WParam := 1;

    Fdispatcher.SendMessage(aMessage);

  end;

end;

procedure TForm1.FormCreate(Sender: TObject);

begin

  {創建消息映射表類}

  Fdispatcher := TPDispatcher.Create;

  Fhandle := TPHandler.Create;

  {創建線程}

    FThread := TPThread.Create(false);

  {向映射表中增加消息}

   Fdispatcher.AddHandle(MY_MESSAGE2,FThread.DoMessage);

end;

procedure TForm1.FormDestroy(Sender: TObject);

var i: Integer;

begin

  FreeAndNil(Fdispatcher);

  FreeAndNil(Fhandle);

  for i:= 0 to 3 do

    FreeAndNil(FThread[i]);

end;

第二。窗口可以處理消息是因為它有窗口句柄。為了使線程也能處理消息，我們可以通過為線程加上一個相應窗口類的窗口名柄。（源碼在 <../消息處理設計(線程)2 / pThread.pas >中）

unit pThread;

interface

uses classes,sysutils,Windows,Messages,Dialogs;

const MY_MESSAGE1 = $BD00 + 01;

Type

{** 消息處理線程類

  *;功能 = 添加線程處理消息能力，

*}

  TPMsgThread = class(TThread)

  private

    //窗口句柄

    FWndHandle: HWND;

    //窗口數據信息

    FWndClass: WNDCLASS;

    //指向窗口回調函數的指針

    FObjectInstance: Pointer;

    //初始化窗口數據

    procedure InitWnd;

    //創建隱藏窗口

    procedure CreateWnd;

    //注冊隱藏窗口

    procedure RegistWnd;

    procedure DestroyWnd;

    //窗口回調函數

    procedure pWndProc(var Message: TMessage); virtual;

  protected

    procedure Execute; override;

    procedure DoTerminate; override;

  public

    constructor Create(CreateSuspended: Boolean); virtual;

    property WndHandle: HWND read FWndHandle write FWndHandle;

  end;

implementation

const WND_NAME = 'PY20';

{ TPMsgThread }

constructor TPMsgThread.Create(CreateSuspended: Boolean);

begin

  inherited Create(CreateSuspended);

  FWndHandle := Integer(nil);

  InitWnd;

  RegistWnd;

  CreateWnd;

end;

procedure TPMsgThread.CreateWnd;

begin

  if(WndHandle = Integer(nil)) then

    WndHandle := CreateWindow(FWndClass.lpszClassName, FWndClass.lpszClassName,

      WS_POPUP or WS_CAPTION or WS_CLipSIBLINGS or WS_SYSMENU

      or WS_MINIMIZEBOX,

      GetSystemMetrics(SM_CXSCREEN) div 2,

      GetSystemMetrics(SM_CYSCREEN) div 2,

      0, 0, 0, 0, FWndClass.hInstance, nil);

  //置換窗口回調函數

  SetWindowLong(WndHandle, GWL_WNDPROC, Longint(FObjectInstance));

end;

procedure TPMsgThread.DestroyWnd;

begin

  UnregisterClass(FWndClass.lpszClassName,FWndClass.hInstance);

  DestroyWindow(WndHandle);

end;

procedure TPMsgThread.DoTerminate;

begin

  inherited;

  DestroyWnd;

end;

procedure TPMsgThread.Execute;

begin

end;

procedure TPMsgThread.InitWnd;

begin

  FwndClass.lpszClassName := PChar(WND_NAME);

  FWndClass.hInstance := Handle;

  FWndClass.lpfnWndProc := @DefWindowProc;

end;

procedure TPMsgThread.pWndProc(var Message: TMessage);

begin

end;

procedure TPMsgThread.RegistWnd;

begin

  FObjectInstance := Classes.MakeObjectInstance(pWndProc);

  if(FWndClass.hInstance <> Integer(nil)) then

    RegisterClass(FWndClass);

end;