Delphi關於線程的消息處理

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裡（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裡建立一張消息映射表，並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;

現在我們只需要註冊一下自定義的消息，然後通過消息分發類（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;

//註冊隱藏窗口

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;