Delphi关于线程的消息处理
在平时写程序时,总是碰到窗体（TForm）与线程（TThread）消息通信问题。令人烦恼的是窗体不能向线程（TThread）发送消息（线程没有窗口句柄）。经过几天的折腾，想出二种解决方案，拿出来跟大家探讨探讨。
第一。我们知道VC++ 中的MFC类库是自已封装了消息处理（BEGINMESSAGE, ENDMESSAGE），在MFC中对消息的处理是通过建立一张消息映射表，而把方法（function）或过程（procedure）的地址保存到映射表里（消息处理实质上是方法或过程的调用）,再加上一个消息分发机制，来实现消息的接收发送 <详见VC++技术内幕>。所以我们只要为线程里建立一张消息映射表，并建立相应的消息分发机制。这样就可以处理窗体发送到线程的消息。以下代码是实现消息映射表和消息分发的类（详见 <..\消息处理设计(线程)1\MessageHandle.pas> 中 ）
unit MessageHandle;
interface
uses messages,Classes,SysUtils,Dialogs;
const PMSG_BASE = $BE00; //自定义消息基址;
PMSG_NUM = 200; //消息表大小；
{**自定义消息处理类
*;功能 = 建立自定义消息表，处理线程之间
* 以及与主窗体之间的自定义消息(宏观)
*}
//消息处理句柄
TMessageHandle = procedure(var Message: TMessage) of Object;
TPDispatcher = class(TObject)
private
//消息对应表(消息ID为数组下标);
MessageHandles: array of TMessageHandle;
//从消息ID得到数组ID
function GetIndexFromMsgID(const aMessageID: cardinal): Integer;
public
constructor Create;
destructor Destroy;
//发送消息
procedure SendMessage(var Message: TMessage); overload;
//添加自定义消息到消息对应表;
procedure AddHandle(const aMessageID: cardinal; aMessageHandle: TMessageHandle);
end;
//
implementation
{ TPDispatcher }
constructor TPDispatcher.Create;
var i: Integer;
begin
SetLength(MessageHandles,PMSG_NUM); //200个消息的消息对应表
//初始化消息队列;
for i := 0 to Pred(PMSG_NUM) do
MessageHandles[i] := nil;
end;
destructor TPDispatcher.Destroy;
begin
{释放消息对应表}
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;
现在我们只需要注册一下自定义的消息，然后通过消息分发类（TPDispatcher），实现对线程消息的处理。代码如下<详见..\消息处理设计(线程)1\test\unit1.pas>：
Unit unit1
const
{自定久线程消息}
MY_MESSAGE2 = PMSG_BASE + 02;
type
TForm1 = class(TForm)
AddMsgList: TButton;
SendThead: TButton;
sendForm: TButton;
sendOther: TButton;
procedure SendTheadClick(Sender: TObject); //发送消息
procedure FormCreate(Sender: TObject);
procedure FormDestroy(Sender: TObject);
private
Fdispatcher: TPDispatcher; 消息映射表类
Fhandle: TPHandler;
FThread: TPTHread; 自定义线程类
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
{创建消息映射表类}
Fdispatcher := TPDispatcher.Create;
Fhandle := TPHandler.Create;
{创建线程}
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。窗口可以处理消息是因为它有窗口句柄。为了使线程也能处理消息，我们可以通过为线程加上一个相应窗口类的窗口名柄。（源码在 <..\消息处理设计(线程)2 \ pThread.pas >中）
unit pThread;
interface
uses classes,sysutils,Windows,Messages,Dialogs;
const MY_MESSAGE1 = $BD00 + 01;
Type
{** 消息处理线程类
*;功能 = 添加线程处理消息能力，
*}
TPMsgThread = class(TThread)
private
//窗口句柄
FWndHandle: HWND;
//窗口数据信息
FWndClass: WNDCLASS;
//指向窗口回调函数的指针
FObjectInstance: Pointer;
//初始化窗口数据
procedure InitWnd;
//创建隐藏窗口
procedure CreateWnd;
//注册隐藏窗口
procedure RegistWnd;
procedure DestroyWnd;
//窗口回调函数
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);
//置换窗口回调函数
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;
