c++窗口过程封装的一些实现

如何封装窗口过程是所有UI库最核心的设计之一，像MFC/WTL/VCL都各有自己的实现代码，最终的目标却是一样的：将窗口过程转化为对象的方法，从而把面向过程的Windows转化为面向对象的方式。这里要介绍我自己想到两种实现方式，这些实现都很简单，但都可以达到同样的目的。
一、利用窗口的属性表
基本原理是将窗口句柄和窗口类实例绑定在一起，每个窗口都有自己的属性表，通过GetProp和SetProp等API操作之，属性表本质上就是哈希表，通过一个Key快速查找到Value，在这里Key就是窗口句柄，Value就是窗口类。
另外，我们需要一个自己的标准窗口过程，用来找到与句柄关联的窗口类，然后再调用窗口类的窗口过程。
先看看实现的代码：
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#ifndef WndHandler_h__
#define WndHandler_h__
#include <crtdbg.h>
#define _WINDOW_CLSATOM "wndatom"
class WndHandler
{
public:
    WndHandler(): mDefWndProc(NULL), mHwnd(NULL)
    {
    }
    virtual ~WndHandler()
    {
        Unsubclass();
    }
    bool Subclass(HWND hwnd)
    {
        Unsubclass();
        _ASSERT(::IsWindow(hwnd));
        _ASSERT(::GetPropA(hwnd, _WINDOW_CLSATOM) == NULL);
        mDefWndProc = (WNDPROC)::GetWindowLongW(hwnd, GWL_WNDPROC);
        if (mDefWndProc == WndHandler::StdWndProc)
            mDefWndProc = DefWindowProcW;
        ::SetWindowLongW(hwnd, GWL_WNDPROC, (long)StdWndProc);
        ::SetPropA(hwnd, _WINDOW_CLSATOM, (HANDLE)this);
        mHwnd = hwnd;
        return true;
    }
    void Unsubclass()
    {
        if (!::IsWindow(mHwnd) || !mDefWndProc)
            return;
        ::SetWindowLongW(mHwnd, (LONG)mDefWndProc, GWL_WNDPROC);
        ::RemovePropA(mHwnd, _WINDOW_CLSATOM);
        mDefWndProc = NULL;
        mHwnd = NULL;
    }
protected:
    static LRESULT CALLBACK StdWndProc(HWND hwnd, UINT msg, WPARAM wparam, LPARAM lparam)
    {
        WndHandler* handler = (WndHandler*)GetPropA(hwnd, _WINDOW_CLSATOM);
        _ASSERT(handler);
        LRESULT ret = 0;
        BOOL done = handler->WndProc(hwnd, msg, wparam, lparam, ret);
        if (done)
            return ret;
        else
            return CallWindowProcW(handler->mDefWndProc, hwnd, msg, wparam, lparam);
    }
    virtual BOOL WndProc(HWND hwnd, UINT msg, WPARAM wparam, LPARAM lparam, LRESULT& ret)
    {
        switch (msg)
        {
        case WM_NCDESTROY:
            {
                mHwnd = NULL;
                break;
            }
        }
        return FALSE;
    }
protected:
    WNDPROC     mDefWndProc;
    HWND        mHwnd;
};
#endif // WndHandler_h__
#ifndef WndHandler_h__
#define WndHandler_h__
#include <crtdbg.h>
#define _WINDOW_CLSATOM "wndatom"
class WndHandler
{
public:
    WndHandler(): mDefWndProc(NULL), mHwnd(NULL)
    {
    }
    virtual ~WndHandler()
    {
        Unsubclass();
    }
    bool Subclass(HWND hwnd)
    {
        Unsubclass();
        _ASSERT(::IsWindow(hwnd));
        _ASSERT(::GetPropA(hwnd, _WINDOW_CLSATOM) == NULL);
        mDefWndProc = (WNDPROC)::GetWindowLongW(hwnd, GWL_WNDPROC);
        if (mDefWndProc == WndHandler::StdWndProc)
            mDefWndProc = DefWindowProcW;
        ::SetWindowLongW(hwnd, GWL_WNDPROC, (long)StdWndProc);
        ::SetPropA(hwnd, _WINDOW_CLSATOM, (HANDLE)this);
        mHwnd = hwnd;
        return true;
    }
    void Unsubclass()
    {
        if (!::IsWindow(mHwnd) || !mDefWndProc)
            return;
        ::SetWindowLongW(mHwnd, (LONG)mDefWndProc, GWL_WNDPROC);
        ::RemovePropA(mHwnd, _WINDOW_CLSATOM);
        mDefWndProc = NULL;
        mHwnd = NULL;
    }
protected:
    static LRESULT CALLBACK StdWndProc(HWND hwnd, UINT msg, WPARAM wparam, LPARAM lparam)
    {
        WndHandler* handler = (WndHandler*)GetPropA(hwnd, _WINDOW_CLSATOM);
        _ASSERT(handler);
        LRESULT ret = 0;
        BOOL done = handler->WndProc(hwnd, msg, wparam, lparam, ret);
        if (done)
            return ret;
        else
            return CallWindowProcW(handler->mDefWndProc, hwnd, msg, wpa

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