Windows API 编程-----Windows NT 环境下禁止任务切换

函数原型：
BOOL WINAPI SystemParametersInfo(
  _In_    UINT  uiAction,
  _In_    UINT  uiParam,
  _Inout_ PVOID pvParam,
  _In_    UINT  fWinIni
);
//函数 MSDN链接：https://msdn.microsoft.com/en-us/library/ms724947(v=vs.85).aspx

用法：
UINT nPreviousState;
//禁止任务切换
SystemParametersInfo(SPI_SETSCREENSAVERRUNNING,TRUE,&nPreviousState,)

//允许任务切换
SystemParametersInfo(SPI_SETSCREENSAVERRUNNING,FALSE,&nPreviousState,);

代码示例：

// DisableChangeTask.cpp : 定义应用程序的入口点。
//

#include "stdafx.h"
#include "DisableChangeTask.h"

#define MAX_LOADSTRING 100
typedef struct _DLONG
{
    LONG wParam;
    LONG lParam;
}DLONG;

// 全局变量:
HINSTANCE hInst;                                // 当前实例
WCHAR szTitle[MAX_LOADSTRING];                  // 标题栏文本
WCHAR szWindowClass[MAX_LOADSTRING];            // 主窗口类名

// 此代码模块中包含的函数的前向声明:
ATOM                MyRegisterClass(HINSTANCE hInstance);
BOOL                InitInstance(HINSTANCE, int);
LRESULT CALLBACK    WndProc(HWND, UINT, WPARAM, LPARAM);
INT_PTR CALLBACK    About(HWND, UINT, WPARAM, LPARAM);

//MyFunction，就是用这个函数来处理消息
BOOL CALLBACK EnumWindowsProc(HWND hwnd, LPARAM lParam);

int APIENTRY wWinMain(_In_ HINSTANCE hInstance,
                     _In_opt_ HINSTANCE hPrevInstance,
                     _In_ LPWSTR    lpCmdLine,
                     _In_ int       nCmdShow)
{
    UNREFERENCED_PARAMETER(hPrevInstance);
    UNREFERENCED_PARAMETER(lpCmdLine);
    if (lpCmdLine != NULL)
    {
        if (lstrlen(lpCmdLine) >= ) {
            MessageBox(NULL, lpCmdLine, TEXT("This is the cmdline"), MB_OK);
        }
    }

    // TODO: 在此放置代码。

    // 初始化全局字符串
    LoadStringW(hInstance, IDS_APP_TITLE, szTitle, MAX_LOADSTRING);
    LoadStringW(hInstance, IDC_DISABLECHANGETASK, szWindowClass, MAX_LOADSTRING);
    MyRegisterClass(hInstance);

    // 执行应用程序初始化:
    if (!InitInstance (hInstance, nCmdShow))
    {
        return FALSE;
    }

    HACCEL hAccelTable = LoadAccelerators(hInstance, MAKEINTRESOURCE(IDC_DISABLECHANGETASK));

    MSG msg;

    // 主消息循环:
    while (GetMessage(&msg, nullptr, , ))
    {
        if (!TranslateAccelerator(msg.hwnd, hAccelTable, &msg))
        {
            TranslateMessage(&msg);
            DispatchMessage(&msg);
        }
    }

    return (int) msg.wParam;
}

//
//  函数: MyRegisterClass()
//
//  目的: 注册窗口类。
//
ATOM MyRegisterClass(HINSTANCE hInstance)
{
    WNDCLASSEXW wcex;

    wcex.cbSize = sizeof(WNDCLASSEX);

    wcex.style          = CS_HREDRAW | CS_VREDRAW;
    wcex.lpfnWndProc    = WndProc;
    wcex.cbClsExtra     = ;
    wcex.cbWndExtra     = ;
    wcex.hInstance      = hInstance;
    wcex.hIcon          = LoadIcon(hInstance, MAKEINTRESOURCE(IDI_DISABLECHANGETASK));
    wcex.hCursor        = LoadCursor(nullptr, IDC_ARROW);
    wcex.hbrBackground  = (HBRUSH)(COLOR_WINDOW+);
    wcex.lpszMenuName   = MAKEINTRESOURCEW(IDC_DISABLECHANGETASK);
    wcex.lpszClassName  = szWindowClass;
    wcex.hIconSm        = LoadIcon(wcex.hInstance, MAKEINTRESOURCE(IDI_SMALL));

    return RegisterClassExW(&wcex);
}

//
//   函数: InitInstance(HINSTANCE, int)
//
//   目的: 保存实例句柄并创建主窗口
//
//   注释:
//
//        在此函数中，我们在全局变量中保存实例句柄并
//        创建和显示主程序窗口。
//
BOOL InitInstance(HINSTANCE hInstance, int nCmdShow)
{
   hInst = hInstance; // 将实例句柄存储在全局变量中

   HWND hWnd = CreateWindowW(szWindowClass, szTitle, WS_OVERLAPPEDWINDOW,
      CW_USEDEFAULT, , CW_USEDEFAULT, , nullptr, nullptr, hInstance, nullptr);

   if (!hWnd)
   {
      return FALSE;
   }
/********************************my code goes here***************************/
   BOOL old;
   DLONG dlong;
   dlong.wParam = (WPARAM)hWnd;
   dlong.lParam = (LPARAM)FALSE;
   EnumWindows(EnumWindowsProc, (LONG)&dlong);
   //借助于屏幕保护程序欺骗操作系统禁止Alt+Tab/Esc
   SystemParametersInfo(SPI_SCREENSAVERRUNNING, TRUE, &old, );
/********************************my code goes up there***********************/

   ShowWindow(hWnd, nCmdShow);
   UpdateWindow(hWnd);

   return TRUE;
}

//
//  函数: WndProc(HWND, UINT, WPARAM, LPARAM)
//
//  目的:    处理主窗口的消息。
//
//  WM_COMMAND  - 处理应用程序菜单
//  WM_PAINT    - 绘制主窗口
//  WM_DESTROY  - 发送退出消息并返回
//
//
LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    switch (message)
    {
        /*****************my code goes below***************/
    case WM_SYSCOMMAND:
        if (wParam == SC_MINIMIZE) return ;
        return DefWindowProc(hWnd, message, wParam, lParam);
        break;
        /*****************my code goes above***************/
    case WM_COMMAND:
        {
            int wmId = LOWORD(wParam);
            // 分析菜单选择:
            switch (wmId)
            {
            case IDM_ABOUT:
                DialogBox(hInst, MAKEINTRESOURCE(IDD_ABOUTBOX), hWnd, About);
                break;
            case IDM_EXIT:
                DestroyWindow(hWnd);
                break;
            default:
                return DefWindowProc(hWnd, message, wParam, lParam);
            }
        }
        break;
    case WM_PAINT:
        {
            PAINTSTRUCT ps;
            HDC hdc = BeginPaint(hWnd, &ps);
            // TODO: 在此处添加使用 hdc 的任何绘图代码...
            EndPaint(hWnd, &ps);
        }
        break;
    case WM_DESTROY:

        /*******当退出当前窗口是就允许任务切换了*********/

        DLONG dlong;
        BOOL Old;
        dlong.lParam = (LPARAM)TRUE;
        dlong.wParam = (WPARAM)hWnd;
        EnumWindows(EnumWindowsProc, (LONG)&Old);
        SystemParametersInfo(SPI_SCREENSAVERRUNNING, FALSE, &Old, );
        /*******当退出当前窗口是就允许任务切换了*********/
        PostQuitMessage();
        break;
    default:
        return DefWindowProc(hWnd, message, wParam, lParam);
    }
    return ;
}

// “关于”框的消息处理程序。
INT_PTR CALLBACK About(HWND hDlg, UINT message, WPARAM wParam, LPARAM lParam)
{
    UNREFERENCED_PARAMETER(lParam);
    switch (message)
    {
    case WM_INITDIALOG:
        return (INT_PTR)TRUE;

    case WM_COMMAND:
        if (LOWORD(wParam) == IDOK || LOWORD(wParam) == IDCANCEL)
        {
            EndDialog(hDlg, LOWORD(wParam));
            return (INT_PTR)TRUE;
        }
        break;
    }
    return (INT_PTR)FALSE;
}

BOOL CALLBACK EnumWindowsProc(HWND hwnd, LPARAM lParam)
{
    DLONG *pDlong = (DLONG*)lParam;
    BOOL bEnable = (BOOL)pDlong->lParam;
    if (hwnd != (HWND)pDlong->wParam)
        EnableWindow(hwnd, bEnable);
    return TRUE;
}

运行结果：如图，如果不关闭运行的界面，就无法切换到其他任务：