【摘要】這節課的主要內容是將如何修改視窗類，也就是修改一個建立好的視窗類。本節課實現修改我們自己建立的視窗類，來達到閃爍的文字和視窗背景顏色的效果。當然也可以修改系統建立的視窗類。

修改視窗類，系統已經提供了API函式SetWindowLong。它可以修改已經建立的視窗的風格、視窗過程、視窗ID和視窗關聯的資料。
修改的實現過程很簡單。我們利用這個修改，可以隨意切換視窗處理過程。只要修改一下視窗過程，視窗的訊息就會發送到新的視窗過程中處理了。
首先，準備好一個視窗過程。自己提供的視窗過程中，包含了另外一套訊息處理。和原先的視窗過程一起，一共有兩套了。
然後通過使用SetWindowLong(hwnd, GWL_WNDPROC, (LONG)新視窗過程函式名)，這樣就可以重新設定了。SetWindowLong需要設定的視窗控制代碼，所以，你要等開始的視窗已經建立成功了，才能設定，不然你無法獲取視窗控制代碼咯。你也可以等視窗創建出來後再給視窗類修改視窗過程，也可以建立視窗後，修改視窗類的視窗過程，然後再顯示視窗

#include <Windows.h>
#include <tchar.h>

LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);
LRESULT CALLBACK MyProc(HWND, UINT, WPARAM, LPARAM);

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrev, PSTR szCmdLine, int iCmdShow)
{
    static TCHAR szExeName[] = _T("Win32");
    HWND hwnd;
    MSG  msg;
    WNDCLASS wndclass;

    wndclass.style = CS_HREDRAW | CS_VREDRAW;
    wndclass.lpfnWndProc = WndProc;
    wndclass.cbClsExtra = 0;
    wndclass.cbWndExtra = 0;
    wndclass.hInstance = hInstance;
    wndclass.hIcon = LoadIcon(NULL, IDI_APPLICATION);
    wndclass.hCursor = LoadCursor(NULL, IDC_ARROW);
    wndclass.hbrBackground = (HBRUSH)GetStockObject(WHITE_BRUSH);
    wndclass.lpszMenuName = NULL;
    wndclass.lpszClassName = szExeName;
	

    if (!RegisterClass(&wndclass))
    {
        MessageBox(NULL, _T("註冊視窗類失敗，此程式需要執行在Windows NT平臺下。"), szExeName, MB_ICONERROR);
        return 0;
    }

    hwnd = CreateWindow(szExeName, _T("我的視窗標題_C++技術網"), WS_OVERLAPPEDWINDOW, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, NULL, NULL, hInstance, NULL);

    SetWindowLong(hwnd, GWL_WNDPROC, (LONG)MyProc);
    ShowWindow(hwnd, iCmdShow);
    UpdateWindow(hwnd);

    while (GetMessage(&msg, NULL, 0, 0))
    {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }
    return msg.wParam;
}
LRESULT CALLBACK MyProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    HDC hdc;
    PAINTSTRUCT ps;
    RECT rect;
    static int i = 0;
    WCHAR szTip[100] = { 0 };
    switch (message)
    {
    case WM_CREATE:
        MessageBox(NULL, _T("視窗正在建立"), _T("win32"), MB_ICONINFORMATION);
        SetTimer(hwnd, 0, 1000, NULL);
        return 0;
    case WM_PAINT:
       hdc = BeginPaint(hwnd, &ps);
       GetClientRect(hwnd, &rect);
       SetBkColor(hdc, RGB(0, 0, 255));
       SetTextColor(hdc, RGB(255, 0, 0));
       FillRect(GetWindowDC(hwnd), &rect, (HBRUSH)GetStockObject(WHITE_BRUSH));
       DrawText(hdc, _T("Win32程式介面，初始化視窗過程"), -1, &rect, DT_SINGLELINE | DT_CENTER | DT_VCENTER);
       SetWindowLong(hwnd, GWL_WNDPROC, (LONG)WndProc);//- 切換視窗過程
       swprintf(szTip,100, _T("計時：%d"), i);
       DrawText(hdc, szTip, -1, &rect, DT_SINGLELINE | DT_CENTER);
       EndPaint(hwnd, &ps);
       return 0;
    case WM_DESTROY:
        MessageBox(NULL, _T("程式即將結束！"), _T("win32"), MB_ICONINFORMATION);
        KillTimer(hwnd, 0);
        PostQuitMessage(0);
        return 0;
    case WM_TIMER:
        GetClientRect(hwnd, &rect);
        InvalidateRect(hwnd, &rect, true);
        i++;
        return 0;
    }
    return DefWindowProc(hwnd, message, wParam, lParam);
}

LRESULT CALLBACK WndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    HDC hdc;
    PAINTSTRUCT ps;
    RECT rect;
    static int i = 0;
    WCHAR szTip[100] = { 0 };
    switch (message)
    {
    case WM_CREATE:
        MessageBox(NULL, _T("視窗正在建立"), _T("win32"), MB_ICONINFORMATION);
        SetTimer(hwnd, 0, 1000, NULL);
        return 0;
    case WM_PAINT:
       hdc = BeginPaint(hwnd, &ps);
       GetClientRect(hwnd, &rect);
       SetBkColor(hdc, RGB(0, 0, 255));
       SetTextColor(hdc, RGB(255, 0, 0));
       FillRect(GetWindowDC(hwnd), &rect, (HBRUSH)GetStockObject(WHITE_BRUSH));
       DrawText(hdc, _T("Win32程式介面，初始化視窗過程"), -1, &rect, DT_SINGLELINE | DT_CENTER | DT_VCENTER);
       SetWindowLong(hwnd, GWL_WNDPROC, (LONG)MyProc);//- 切換視窗過程
       swprintf(szTip,100, _T("計時：%d"), i);
       DrawText(hdc, szTip, -1, &rect, DT_SINGLELINE | DT_CENTER);
       EndPaint(hwnd, &ps);
       return 0;
    case WM_DESTROY:
        MessageBox(NULL, _T("程式即將結束！"), _T("win32"), MB_ICONINFORMATION);
        KillTimer(hwnd, 0);
        PostQuitMessage(0);
        return 0;
    case WM_TIMER:
        GetClientRect(hwnd, &rect);
        InvalidateRect(hwnd, &rect, true);
        i++;
        return 0;
    }
    return DefWindowProc(hwnd, message, wParam, lParam);
}