C++ builder消息的运用

http://tech.e800.com.cn/articles/2010/17/1262842530085_1.html

一、TApplication的OnMessage事件
OnMessage事件只处理消息队列中的消息，SendMessage()发送的消息不会被截获。
任何窗体接收到一个windows消息，都会触发一次此事件
函数原型：
typedef void __fastcall (__closure *TMessageEvent) (tagMSG &Msg,bool &Handled);
Msg表示被截获的消息，Handled表示是否处理完成，为TRUE则防止被再次处理，设为FALSE则可以继续处理。

//计算程序响应的消息数
//---------------------------------------------------------------------------

#ifndef Msg_testH
#define Msg_testH
//---------------------------------------------------------------------------
#include <Classes.hpp>
#include <Controls.hpp>
#include <StdCtrls.hpp>
#include <Forms.hpp>
//---------------------------------------------------------------------------
class TForm1 : public TForm
{
__published:    // IDE-managed Components
    TLabel *Label1;
    void __fastcall FormCreate(TObject *Sender);
private:    // User declarations
    //自定义消息响应函数
    void __fastcall AppMessage(tagMSG &MSG,bool &Handled);
public:        // User declarations
    __fastcall TForm1(TComponent* Owner);
    int Num;
};
//---------------------------------------------------------------------------
extern PACKAGE TForm1 *Form1;
//---------------------------------------------------------------------------
#endif

//---------------------------------------------------------------------------

#include <vcl.h>
#pragma hdrstop

#include "Msg_test.h"
//---------------------------------------------------------------------------
#pragma package(smart_init)
#pragma resource "*.dfm"
TForm1 *Form1;
//---------------------------------------------------------------------------
__fastcall TForm1::TForm1(TComponent* Owner)
    : TForm(Owner)
{
    Num = 0;
}
//---------------------------------------------------------------------------

void __fastcall TForm1::FormCreate(TObject *Sender)
{
    //将自定义函数与OnMessage事件联系起来
    Application->OnMessage = AppMessage;
}
//---------------------------------------------------------------------------
void __fastcall TForm1::AppMessage(tagMSG &MSG,bool &Handled)
{
    Num++;
    Label1->Caption = AnsiString(Num);
    Handled = false;
}

//计算程序响应的消息数
//---------------------------------------------------------------------------

#ifndef Msg_testH
#define Msg_testH
//---------------------------------------------------------------------------
#include <Classes.hpp>
#include <Controls.hpp>
#include <StdCtrls.hpp>
#include <Forms.hpp>
//---------------------------------------------------------------------------
class TForm1 : public TForm
{
__published:    // IDE-managed Components
    TLabel *Label1;
    void __fastcall FormCreate(TObject *Sender);
private:    // User declarations
    //自定义消息响应函数
    void __fastcall AppMessage(tagMSG &MSG,bool &Handled);
public:        // User declarations
    __fastcall TForm1(TComponent* Owner);
    int Num;
};
//---------------------------------------------------------------------------
extern PACKAGE TForm1 *Form1;
//---------------------------------------------------------------------------
#endif

//---------------------------------------------------------------------------

#include <vcl.h>
#pragma hdrstop

#include "Msg_test.h"
//---------------------------------------------------------------------------
#pragma package(smart_init)
#pragma resource "*.dfm"
TForm1 *Form1;
//---------------------------------------------------------------------------
__fastcall TForm1::TForm1(TComponent* Owner)
    : TForm(Owner)
{
    Num = 0;
}
//---------------------------------------------------------------------------

void __fastcall TForm1::FormCreate(TObject *Sender)
{
    //将自定义函数与OnMessage事件联系起来
    Application->OnMessage = AppMessage;
}
//---------------------------------------------------------------------------
void __fastcall TForm1::AppMessage(tagMSG &MSG,bool &Handled)
{
    Num++;
    Label1->Caption = AnsiString(Num);
    Handled = false;
}

二、消息映射

使用消息映射，一般需要三步：

(1).声明消息映射表，把某些消息的处理权，交给自己定义的函数
以一个没有参数的BEGIN_MESSAGE_MAP宏开始，
以END_MESSAGE_MAP宏结束(唯一参数是组件的父类的名字，通常为TForm)
在中间插入一个或多个MESSAGE_HANDLER宏，其将一个消息句柄和一个消息处理函数联系在一起。
MESSAGE_HANDLER(windows消息名，消息结构体名，消息处理函数名）

(2)声明消息处理函数
函数名称和参数必须和MESSAGE_HANDLER宏定义的一样

(3)实现消息处理函数
与一般类函数差不多，只是在最后加上一条语句，完成VCL对消息的默认处理
TForm::Dispatch(&Message);

//---------------------------------------------------------------------------

#ifndef Unit1H
#define Unit1H
//---------------------------------------------------------------------------
#include <Classes.hpp>
#include <Controls.hpp>
#include <StdCtrls.hpp>
#include <Forms.hpp>
//---------------------------------------------------------------------------
class TForm1 : public TForm
{
__published:    // IDE-managed Components
    TLabel *Label1;
private:    // User declarations
public:        // User declarations
    __fastcall TForm1(TComponent* Owner);

    //自定义消息映射函数
    void __fastcall WMGetMinMaxInfo(TWMGetMinMaxInfo &Msg);

BEGIN_MESSAGE_MAP
    MESSAGE_HANDLER(WM_GETMINMAXINFO,TWMGetMinMaxInfo,WMGetMinMaxInfo)
END_MESSAGE_MAP(TForm)
};
//---------------------------------------------------------------------------
extern PACKAGE TForm1 *Form1;
//---------------------------------------------------------------------------
#endif
 
 
 //---------------------------------------------------------------------------

#include <vcl.h>
#pragma hdrstop

#include "Unit1.h"
//---------------------------------------------------------------------------
#pragma package(smart_init)
#pragma resource "*.dfm"
TForm1 *Form1;
//---------------------------------------------------------------------------
__fastcall TForm1::TForm1(TComponent* Owner)
    : TForm(Owner)
{
}
//---------------------------------------------------------------------------
void __fastcall TForm1::WMGetMinMaxInfo(TWMGetMinMaxInfo &Msg)
{
    //当用户单击窗体状态栏上的最大化按钮时，限制窗体的长宽
    Msg.MinMaxInfo->ptMaxSize.x = 600;
    Msg.MinMaxInfo->ptMaxSize.y = 400;

    //设定窗体最大化时，左上角左边为窗体当前位置
    Msg.MinMaxInfo->ptMaxPosition.x = Left;
    Msg.MinMaxInfo->ptMaxPosition.y = Top;

    //当用户用鼠标拖动的方式改变窗体尺寸时，限制其最大值
    Msg.MinMaxInfo->ptMaxTrackSize.x = 600;
    Msg.MinMaxInfo->ptMaxTrackSize.y = 400;

    //当用户用鼠标拖动的方式改变窗体尺寸时，限制其最小值
    Msg.MinMaxInfo->ptMinTrackSize.x = 200;
    Msg.MinMaxInfo->ptMinTrackSize.y = 10;

    //显示当前窗体的尺寸
    Label1->Caption = "Width:" + AnsiString(this->Width)+
            " Height: " + AnsiString(Height);

    TForm::Dispatch(&Msg);
}

//---------------------------------------------------------------------------

#ifndef Unit1H
#define Unit1H
//---------------------------------------------------------------------------
#include <Classes.hpp>
#include <Controls.hpp>
#include <StdCtrls.hpp>
#include <Forms.hpp>
//---------------------------------------------------------------------------
class TForm1 : public TForm
{
__published:    // IDE-managed Components
    TLabel *Label1;
private:    // User declarations
public:        // User declarations
    __fastcall TForm1(TComponent* Owner);

    //自定义消息映射函数
    void __fastcall WMGetMinMaxInfo(TWMGetMinMaxInfo &Msg);

BEGIN_MESSAGE_MAP
    MESSAGE_HANDLER(WM_GETMINMAXINFO,TWMGetMinMaxInfo,WMGetMinMaxInfo)
END_MESSAGE_MAP(TForm)
};
//---------------------------------------------------------------------------
extern PACKAGE TForm1 *Form1;
//---------------------------------------------------------------------------
#endif
 
 
 //---------------------------------------------------------------------------

#include <vcl.h>
#pragma hdrstop

#include "Unit1.h"
//---------------------------------------------------------------------------
#pragma package(smart_init)
#pragma resource "*.dfm"
TForm1 *Form1;
//---------------------------------------------------------------------------
__fastcall TForm1::TForm1(TComponent* Owner)
    : TForm(Owner)
{
}
//---------------------------------------------------------------------------
void __fastcall TForm1::WMGetMinMaxInfo(TWMGetMinMaxInfo &Msg)
{
    //当用户单击窗体状态栏上的最大化按钮时，限制窗体的长宽
    Msg.MinMaxInfo->ptMaxSize.x = 600;
    Msg.MinMaxInfo->ptMaxSize.y = 400;

    //设定窗体最大化时，左上角左边为窗体当前位置
    Msg.MinMaxInfo->ptMaxPosition.x = Left;
    Msg.MinMaxInfo->ptMaxPosition.y = Top;

    //当用户用鼠标拖动的方式改变窗体尺寸时，限制其最大值
    Msg.MinMaxInfo->ptMaxTrackSize.x = 600;
    Msg.MinMaxInfo->ptMaxTrackSize.y = 400;

    //当用户用鼠标拖动的方式改变窗体尺寸时，限制其最小值
    Msg.MinMaxInfo->ptMinTrackSize.x = 200;
    Msg.MinMaxInfo->ptMinTrackSize.y = 10;

    //显示当前窗体的尺寸
    Label1->Caption = "Width:" + AnsiString(this->Width)+
            " Height: " + AnsiString(Height);

    TForm::Dispatch(&Msg);
}

三、消息映射的深入讨论

../include/vcl/sysmac.h中有消息映射的宏定义

#define BEGIN_MESSAGE_MAP   virtual void __fastcall Dispatch(void *Message) \
        {                                           \
          switch  (((PMessage)Message)->Msg)        \
          {

#define VCL_MESSAGE_HANDLER(msg,type,meth)          \
          case    msg:                              \
            meth(*((type *)Message));               \
            break;

// NOTE: ATL defines a MESSAGE_HANDLER macro which conflicts with VCL's macro. The
//       VCL macro has been renamed to VCL_MESSAGE_HANDLER. If you are not using ATL,
//       MESSAGE_HANDLER is defined as in previous versions of BCB.
//
#if !defined(USING_ATL) && !defined(USING_ATLVCL) && !defined(INC_ATL_HEADERS)
#define MESSAGE_HANDLER  VCL_MESSAGE_HANDLER
#endif // ATL_COMPAT

#define END_MESSAGE_MAP(base)           default:    \
                        base::Dispatch(Message);    \
                        break;                      \
          }                                         \
        }
        
//对与消息映射：
BEGIN_MESSAGE_MAP
    MESSAGE_HANDLER(WM_GETMINMAXINFO,TWMGetMinMaxInfo,WMGetMinMaxInfo)
END_MESSAGE_MAP(TForm1)

//将被扩展为：
virtual void __fastcall Dispatch(void *Message) 
        {                                           
          switch  (((PMessage)Message)->Msg)        
          {
          case    msg:                              
            WMGetMinMaxInfo(*((TWMGetMinMaxInfo*)Message));               
            break;
          default:    
            TForm1::Dispatch(Message);    
            break;                      
          }                                         
        }

#define BEGIN_MESSAGE_MAP   virtual void __fastcall Dispatch(void *Message) \
        {                                           \
          switch  (((PMessage)Message)->Msg)        \
          {

#define VCL_MESSAGE_HANDLER(msg,type,meth)          \
          case    msg:                              \
            meth(*((type *)Message));               \
            break;

// NOTE: ATL defines a MESSAGE_HANDLER macro which conflicts with VCL's macro. The
//       VCL macro has been renamed to VCL_MESSAGE_HANDLER. If you are not using ATL,
//       MESSAGE_HANDLER is defined as in previous versions of BCB.
//
#if !defined(USING_ATL) && !defined(USING_ATLVCL) && !defined(INC_ATL_HEADERS)
#define MESSAGE_HANDLER  VCL_MESSAGE_HANDLER
#endif // ATL_COMPAT

#define END_MESSAGE_MAP(base)           default:    \
                        base::Dispatch(Message);    \
                        break;                      \
          }                                         \
        }
        
//对与消息映射：
BEGIN_MESSAGE_MAP
    MESSAGE_HANDLER(WM_GETMINMAXINFO,TWMGetMinMaxInfo,WMGetMinMaxInfo)
END_MESSAGE_MAP(TForm1)

//将被扩展为：
virtual void __fastcall Dispatch(void *Message) 
        {                                           
          switch  (((PMessage)Message)->Msg)        
          {
          case    msg:                              
            WMGetMinMaxInfo(*((TWMGetMinMaxInfo*)Message));               
            break;
          default:    
            TForm1::Dispatch(Message);    
            break;                      
          }                                         
        }

VCL_MESSAGE_HANDLER写法，是为了调用ATL时，命名不冲突

四、重载WndProc()函数

函数原型：
virtual void __fastcall WndProc(Message::TMessage &Message);

//头文件中声明
void __fastcall WndProc(TMessage &Message);

//实现文件
void __fastcall TForm1::WndProc(TMessage &Message)
{
    if(Message.Msg == WM_GETMINMAXINFO)
    {
        //付给结构体LPMINMAXINFO
        LPMINMAXINFO lpmmi = (LPMINMAXINFO)Message.LParam;

        //当用户单击窗体状态栏上的最大化按钮时，限制窗体的长宽
        lpmmi->ptMaxSize.x = 600;
        lpmmi->ptMaxSize.y = 400;

        //设定窗体最大化时，左上角左边为窗体当前位置
        lpmmi->ptMaxPosition.x = Left;
        lpmmi->ptMaxPosition.y = Top;

        //当用户用鼠标拖动的方式改变窗体尺寸时，限制其最大值
        lpmmi->ptMaxTrackSize.x = 600;
        lpmmi->ptMaxTrackSize.y = 400;

        //当用户用鼠标拖动的方式改变窗体尺寸时，限制其最小值
        lpmmi->ptMinTrackSize.x = 200;
        lpmmi->ptMinTrackSize.y = 100;

        //显示当前窗体的尺寸
        Label1->Caption = "Width:" + AnsiString(this->Width)+
                " Height: " + AnsiString(Height);
    }
    TForm::WndProc(Message);
}

//头文件中声明
void __fastcall WndProc(TMessage &Message);

//实现文件
void __fastcall TForm1::WndProc(TMessage &Message)
{
    if(Message.Msg == WM_GETMINMAXINFO)
    {
        //付给结构体LPMINMAXINFO
        LPMINMAXINFO lpmmi = (LPMINMAXINFO)Message.LParam;

        //当用户单击窗体状态栏上的最大化按钮时，限制窗体的长宽
        lpmmi->ptMaxSize.x = 600;
        lpmmi->ptMaxSize.y = 400;

        //设定窗体最大化时，左上角左边为窗体当前位置
        lpmmi->ptMaxPosition.x = Left;
        lpmmi->ptMaxPosition.y = Top;

        //当用户用鼠标拖动的方式改变窗体尺寸时，限制其最大值
        lpmmi->ptMaxTrackSize.x = 600;
        lpmmi->ptMaxTrackSize.y = 400;

        //当用户用鼠标拖动的方式改变窗体尺寸时，限制其最小值
        lpmmi->ptMinTrackSize.x = 200;
        lpmmi->ptMinTrackSize.y = 100;

        //显示当前窗体的尺寸
        Label1->Caption = "Width:" + AnsiString(this->Width)+
                " Height: " + AnsiString(Height);
    }
    TForm::WndProc(Message);
}

五、非标准消息
1.通知消息(Notification message)
此消息只发生在一些标准windows控件上
当一个窗体的子控件发生了一些事情后，他通知给其父窗体的消息
包括：按钮、编辑框、列表空、label等..
如：BN_CLICKED 单击按钮

2.自定义消息
相比通过改变对象成员的优点：可以不用知道接收者的确切类型，只要知道其窗口句柄；可以广播给多个接受者。
一般有两种方式：直接定义，WM_USER + XXX 或 WM_APP+XXX 分别为0x0400和0x8000
或调用API函数RegisterWindowMessage()向系统注册一个

3.发送自定义消息
向特定窗体发送消息：
TControl::Perform() 由C++ builder提供
SendMessage() 和 PostMessage() API函数

发送广播消息
TWinControl::Broadcast()  由C++ builder提供
BroadcastSystemMessage()  API函数

Perform() 适用于在同一应用程序的不同窗体和控件消息的传递。
SendMessage() 把消息直接发送给窗口函数(不入队列)，等消息被处理后才返回。
PostMessage() 只是单纯吧消息送到消息队列中，就立刻返回。
Boradcast() 只能向C++ builder应用程序中的指定窗体上的所有子控件广播消息，无法向其他应用程序广播。
BroadcastSystemMessage() 可以向任意的应用程序或者组件广播消息。

//窗体1(四个按钮)
//---------------------------------------------------------------------------

#ifndef Unit1H
#define Unit1H
//---------------------------------------------------------------------------
#include <Classes.hpp>
#include <Controls.hpp>
#include <StdCtrls.hpp>
#include <Forms.hpp>

#include "Unit2.h"
//---------------------------------------------------------------------------
class TForm1 : public TForm
{
__published:    // IDE-managed Components
    TButton *Button1;
    TButton *Button2;
    TButton *Button3;
    TButton *Button4;
    void __fastcall Button1Click(TObject *Sender);
    void __fastcall Button2Click(TObject *Sender);
    void __fastcall Button3Click(TObject *Sender);
    void __fastcall Button4Click(TObject *Sender);
private:    // User declarations
public:        // User declarations
    __fastcall TForm1(TComponent* Owner);
};
//---------------------------------------------------------------------------
extern PACKAGE TForm1 *Form1;
//---------------------------------------------------------------------------
#endif

//---------------------------------------------------------------------------

#include <vcl.h>
#pragma hdrstop

#include "Unit1.h"

//---------------------------------------------------------------------------
#pragma package(smart_init)
#pragma resource "*.dfm"
TForm1 *Form1;
//---------------------------------------------------------------------------
__fastcall TForm1::TForm1(TComponent* Owner)
    : TForm(Owner)
{
}
//---------------------------------------------------------------------------

void __fastcall TForm1::Button1Click(TObject *Sender)
{
    Form2->Perform(WM_CLOSE,0,0);    
}
//---------------------------------------------------------------------------

void __fastcall TForm1::Button2Click(TObject *Sender)
{
    SendMessage(Form2->Handle,WM_CLOSE,0,0);
}
//---------------------------------------------------------------------------

void __fastcall TForm1::Button3Click(TObject *Sender)
{
    PostMessage(Form2->Handle,WM_CLOSE,0,0);
}
//---------------------------------------------------------------------------

void __fastcall TForm1::Button4Click(TObject *Sender)
{
    //向窗体Form2的子控件广播WM_LBUTTONDOWN消息
    TMessage M;
    M.Msg = WM_LBUTTONDOWN;
    Form2->Broadcast(&M);
}
//---------------------------------------------------------------------------


//窗体2(两个panel)
//---------------------------------------------------------------------------

#ifndef Unit2H
#define Unit2H
//---------------------------------------------------------------------------
#include <Classes.hpp>
#include <Controls.hpp>
#include <StdCtrls.hpp>
#include <Forms.hpp>
#include <ExtCtrls.hpp>
//---------------------------------------------------------------------------
class TForm2 : public TForm
{
__published:    // IDE-managed Components
    TPanel *Panel1;
    TPanel *Panel2;
    void __fastcall Panel1MouseDown(TObject *Sender, TMouseButton Button,
          TShiftState Shift, int X, int Y);
    void __fastcall Panel2MouseDown(TObject *Sender, TMouseButton Button,
          TShiftState Shift, int X, int Y);
private:    // User declarations
public:        // User declarations
    __fastcall TForm2(TComponent* Owner);
};
//---------------------------------------------------------------------------
extern PACKAGE TForm2 *Form2;
//---------------------------------------------------------------------------
#endif


//---------------------------------------------------------------------------

#include <vcl.h>
#pragma hdrstop

#include "Unit2.h"
//---------------------------------------------------------------------------
#pragma package(smart_init)
#pragma resource "*.dfm"
TForm2 *Form2;
//---------------------------------------------------------------------------
__fastcall TForm2::TForm2(TComponent* Owner)
    : TForm(Owner)
{
}
//---------------------------------------------------------------------------


void __fastcall TForm2::Panel1MouseDown(TObject *Sender,
      TMouseButton Button, TShiftState Shift, int X, int Y)
{
    Panel1->Caption = "Down";
}
//---------------------------------------------------------------------------

void __fastcall TForm2::Panel2MouseDown(TObject *Sender,
      TMouseButton Button, TShiftState Shift, int X, int Y)
{
    Panel2->Caption = "Down";
}
//---------------------------------------------------------------------------

//窗体1(四个按钮)
//---------------------------------------------------------------------------

#ifndef Unit1H
#define Unit1H
//---------------------------------------------------------------------------
#include <Classes.hpp>
#include <Controls.hpp>
#include <StdCtrls.hpp>
#include <Forms.hpp>

#include "Unit2.h"
//---------------------------------------------------------------------------
class TForm1 : public TForm
{
__published:    // IDE-managed Components
    TButton *Button1;
    TButton *Button2;
    TButton *Button3;
    TButton *Button4;
    void __fastcall Button1Click(TObject *Sender);
    void __fastcall Button2Click(TObject *Sender);
    void __fastcall Button3Click(TObject *Sender);
    void __fastcall Button4Click(TObject *Sender);
private:    // User declarations
public:        // User declarations
    __fastcall TForm1(TComponent* Owner);
};
//---------------------------------------------------------------------------
extern PACKAGE TForm1 *Form1;
//---------------------------------------------------------------------------
#endif

//---------------------------------------------------------------------------

#include <vcl.h>
#pragma hdrstop

#include "Unit1.h"

//---------------------------------------------------------------------------
#pragma package(smart_init)
#pragma resource "*.dfm"
TForm1 *Form1;
//---------------------------------------------------------------------------
__fastcall TForm1::TForm1(TComponent* Owner)
    : TForm(Owner)
{
}
//---------------------------------------------------------------------------

void __fastcall TForm1::Button1Click(TObject *Sender)
{
    Form2->Perform(WM_CLOSE,0,0);    
}
//---------------------------------------------------------------------------

void __fastcall TForm1::Button2Click(TObject *Sender)
{
    SendMessage(Form2->Handle,WM_CLOSE,0,0);
}
//---------------------------------------------------------------------------

void __fastcall TForm1::Button3Click(TObject *Sender)
{
    PostMessage(Form2->Handle,WM_CLOSE,0,0);
}
//---------------------------------------------------------------------------

void __fastcall TForm1::Button4Click(TObject *Sender)
{
    //向窗体Form2的子控件广播WM_LBUTTONDOWN消息
    TMessage M;
    M.Msg = WM_LBUTTONDOWN;
    Form2->Broadcast(&M);
}
//---------------------------------------------------------------------------


//窗体2(两个panel)
//---------------------------------------------------------------------------

#ifndef Unit2H
#define Unit2H
//---------------------------------------------------------------------------
#include <Classes.hpp>
#include <Controls.hpp>
#include <StdCtrls.hpp>
#include <Forms.hpp>
#include <ExtCtrls.hpp>
//---------------------------------------------------------------------------
class TForm2 : public TForm
{
__published:    // IDE-managed Components
    TPanel *Panel1;
    TPanel *Panel2;
    void __fastcall Panel1MouseDown(TObject *Sender, TMouseButton Button,
          TShiftState Shift, int X, int Y);
    void __fastcall Panel2MouseDown(TObject *Sender, TMouseButton Button,
          TShiftState Shift, int X, int Y);
private:    // User declarations
public:        // User declarations
    __fastcall TForm2(TComponent* Owner);
};
//---------------------------------------------------------------------------
extern PACKAGE TForm2 *Form2;
//---------------------------------------------------------------------------
#endif


//---------------------------------------------------------------------------

#include <vcl.h>
#pragma hdrstop

#include "Unit2.h"
//---------------------------------------------------------------------------
#pragma package(smart_init)
#pragma resource "*.dfm"
TForm2 *Form2;
//---------------------------------------------------------------------------
__fastcall TForm2::TForm2(TComponent* Owner)
    : TForm(Owner)
{
}
//---------------------------------------------------------------------------


void __fastcall TForm2::Panel1MouseDown(TObject *Sender,
      TMouseButton Button, TShiftState Shift, int X, int Y)
{
    Panel1->Caption = "Down";
}
//---------------------------------------------------------------------------

void __fastcall TForm2::Panel2MouseDown(TObject *Sender,
      TMouseButton Button, TShiftState Shift, int X, int Y)
{
    Panel2->Caption = "Down";
}
//---------------------------------------------------------------------------

六
若自定义消息想带参数，可用LParam和WParam参数
更多可自定义结构体
LPARAM+WPARAM能放下就放,放不下就传指针. SENDMESSAGE可以传局部变量的指针,POSTMESSAGE只能传 全局/局部静态/堆上的 变量的指针.
如：映射到TMessage结构体中，然后取出
void __fastcall myMessage(TMessage &Msg)
{
  int i = Msg.WParam;
}