C++ GetAsyncKeyState 键状态问题

Question

尽管关于这个主题的同一个问题已经被问了很多次，但我找不到任何可行的解决方案。

我的简单程序有两个循环。在我输入凭据并按 Enter 键的那一刻。程序必须进入第一个循环。这样我就可以打印菜单并等待用户输入菜单选择。根据菜单选择，另一个循环必须激活并等待用户输入。

但这里的问题是，当我输入凭据并按 Enter 键时，它会打印菜单并且无需等待用户输入它会进入 1st menu 并显示项目内的第一个菜单。出现这个问题是因为WinAPI的Key state问题

if (GetAsyncKeyState(VR_RETURN) != 0) 将在这两种情况下激活。如果按键被按下。 or 键之前被按下过。

如何解决这个问题？

以下是我的访客登录功能

void guestLogin()
{
    setColor(BASECOLOR);
    clear();

    string screen_lable = "GUEST LOGIN";

    gotoxy(getCenterCoordinatesForText(screen_lable), 2);

    cout << screen_lable << endl;

    gotoxy(getCenterCoordinatesForText(screen_lable), 3);

    for (int i = 0; i < screen_lable.length(); i++)
    {
        cout << "=";
    }

    screen_lable = "PLEASE ENTER YOUR NAME: ";

    gotoxy(getCenterCoordinatesForText(screen_lable), 5);

    gotoxy(getCenterCoordinatesForText(screen_lable), 7);

    getline(cin, username);

    //When user presses enter this will take username and proceed to show menus for the user and it should not go ahead and and select 1st menu and show the content.
    if (username.length() != 0)
    {
        OptionsList();
    }
} 

//用户菜单

void OptionsList()
{
    menuIndex = 0;

    while (true)
    {
        setColor(BASECOLOR);
        clear();

        string appName = "BEST FOOD INFORMATION SYSTEM";
        string menuBtn = "MENUS";
        string catering = "CATERING";
        string services = "SERVICES";
        string helpBtn = "HELP";
        string logoutBtn = "LOGOUT";

        gotoxy(getCenterCoordinatesForText(appName), 2);
        cout << appName << endl;

        /*if (UserRole::Customer)
        {
            gotoxy(getCenterCoordinatesForText(menuBtn + " || " + catering + " || " + helpBtn + " || " + logoutBtn), 5);
        }*/
        //else if (UserRole::Administrator){
            gotoxy(getCenterCoordinatesForText(menuBtn + " || " + catering +" || " + services +  " || " + helpBtn + " || " + logoutBtn), 5);
        //}

        //Updating Screen Text State Based On Key Selection
        if (menuIndex == 0)
        {
            setColor(INVERTED_BASECOLOR);
            cout << menuBtn;
            setColor(BASECOLOR);
            cout << " || ";
            cout << catering;
            cout << " || ";
            cout << services;
            cout << " || ";
            cout << helpBtn;
            cout << " || ";
            cout<< logoutBtn;
        }
        else if (menuIndex == 1)
        {
            setColor(BASECOLOR);
            cout << menuBtn;
            cout << " || ";
            setColor(INVERTED_BASECOLOR);
            cout << catering;
            setColor(BASECOLOR);
            cout << " || ";
            cout << services;
            cout << " || ";
            cout << helpBtn;
            cout << " || ";
            cout << logoutBtn;
        }
        else if (menuIndex == 2)
        {
            setColor(BASECOLOR);
            cout << menuBtn;
            cout << " || ";
            cout << catering;
            cout << " || ";
            setColor(INVERTED_BASECOLOR);
            cout << services;
            setColor(BASECOLOR);
            cout << " || ";
            cout << helpBtn;
            cout << " || ";
            cout << logoutBtn;
        }
        else if (menuIndex == 3)
        {
            setColor(BASECOLOR);
            cout << menuBtn;
            cout << " || ";
            cout << catering;
            cout << " || ";
            cout << services;
            cout << " || ";
            setColor(INVERTED_BASECOLOR);
            cout << helpBtn;
            setColor(BASECOLOR);
            cout << " || ";
            cout << logoutBtn;
        }
        else if (menuIndex == 4)
        {
            setColor(BASECOLOR);
            cout << menuBtn;
            cout << " || ";
            cout << catering;
            cout << " || ";
            cout << services;
            cout << " || ";
            cout << helpBtn;
            cout << " || ";
            setColor(INVERTED_BASECOLOR);
            cout << logoutBtn;
        }

        //Getting Key Events
        while (true)
        {

            if (GetAsyncKeyState(VK_RIGHT) != 0)
            {
                menuIndex += 1;
                if (menuIndex == 5)
                {
                    menuIndex = 4;
                }
                break;
            }
            else if (GetAsyncKeyState(VK_LEFT) != 0)
            {

                menuIndex -= 1;
                if (menuIndex == -1)
                {
                    menuIndex = 0;
                }
                break;
            }
            // Here is the issue occours
            else if (GetAsyncKeyState(VK_RETURN) != 0)
            {

                switch (menuIndex)
                {
                    case 0:
                    {
                        //Previously pressed ENTER Key Stroke evokes this function as the GetAsyncKeyState() returns the pressed state.
                        FoodsNBeverages();
                    } break;
                    case 1:
                    {
                        Catering();
                    } break;
                    case 2:
                    {
                        Services();
                    } break;
                    case 3:
                    {
                        Help();
                    } break;
                    case 4:
                    {
                        Logoff();
                    } break;
                }
            }
        }

        Sleep(200);

    }
}

(GetAsyncKeyState(VK_MENU)&0x8000) 尝试了许多变体，但没有一个有效。

Answer 1

要测试键是否关闭，您需要测试返回值是否设置了 MSB。这在documentation 中有解释。

如果设置了最高有效位，则键向下。

所以替换

GetAsyncKeyState(VK_RETURN) != 0

与

GetAsyncKeyState(VK_RETURN) < 0 

Answer 2

您必须不断使用 GetAsyncKeyState() 函数来检查按键是否被按下。然后，虽然之前已经按下过该键，但没有按下该键时，该函数将返回 0。