Windows API 编程中的组合框

Question

我正在尝试显示一个组合框窗口，如您所见，我将 hWndComboBox 设置为我的第二个窗口，并且我正在使用 ShowWindow() 函数，但它并没有真正显示当我编译并运行代码时有什么吗？我还应该添加什么？

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstace, LPSTR lpCommand, int nCmdLine)
{
    HWND window;
    int xpos = 100;            // Horizontal position of the window.
    int ypos = 100;            // Vertical position of the window.
    int nwidth = 200;          // Width of the window
    int nheight = 200;         // Height of the window
    HWND hwndParent =  window; // Handle to the parent window


    MSG message;
    WNDCLASSEX wndClass;

    wndClass.cbSize = sizeof(WNDCLASSEX);
    wndClass.cbClsExtra = 0;
    wndClass.cbWndExtra = 0;
    wndClass.style = 0;
    wndClass.hInstance = hInstance;
    wndClass.lpfnWndProc = wndCll;
    wndClass.lpszClassName = classNoOne;
    wndClass.lpszMenuName = MAKEINTRESOURCE(IDR_MYMENU);
    wndClass.hIcon = LoadIcon(GetModuleHandle(NULL), MAKEINTRESOURCE(IDI_PENGUIN_ICON));
    wndClass.hIconSm = (HICON)LoadImage(GetModuleHandle(NULL), MAKEINTRESOURCE(IDI_PENGUIN_ICON), IMAGE_ICON, LR_DEFAULTSIZE, LR_DEFAULTSIZE, 0);
    wndClass.hCursor = LoadCursor(NULL, IDC_ARROW);
    wndClass.hbrBackground = (HBRUSH)(COLOR_WINDOW-1);

    if(!RegisterClassEx(&wndClass)){
        printf("No wndclass");
    }
    window = CreateWindowEx(WS_EX_CLIENTEDGE, classNoOne, "Start Window", WS_OVERLAPPEDWINDOW, CW_USEDEFAULT, CW_USEDEFAULT, 1000, 500, NULL, NULL, hInstance, NULL);
        //create the window
    HWND hWndComboBox = CreateWindow(WC_COMBOBOX, "name of the combobox",  CBS_DROPDOWN | CBS_HASSTRINGS | WS_CHILD | WS_OVERLAPPED | WS_VISIBLE , xpos, ypos, nwidth, nheight, hwndParent, NULL, hInstance, NULL);
    TCHAR Planets[9][10] = {
        TEXT("MERCURY"), TEXT("VENUS"), TEXT("Terra"), TEXT("MARS"), TEXT("JUPITER"), TEXT("SATURN"), TEXT("URANUS"), TEXT("NEPTUNE"), TEXT("PLUTO")
    };
    //these are the list elements
    TCHAR A[16];
    int k = 0;
    memset(&A, 0, sizeof(A));
    //allocate memory
    for(k = 0; k<=8; k+=1){
    strcpy(A, (TCHAR *)Planets[k]);
      SendMessage(hWndComboBox,(UINT) CB_ADDSTRING,(WPARAM) 0,(LPARAM) A);
    }
    SendMessage(hWndComboBox, CB_SETCURSEL, (WPARAM)2, (LPARAM)0);
    ShowWindow(hWndComboBox, nCmdLine);
   //ShowWindow(window, nCmdLine);
    if(window == NULL){
        printf("window is NULL");
    }

    while(GetMessage(&message, NULL, 0, 0) > 0){
            if(!IsDialogMessage(dialogSmall, &message)){
                TranslateMessage(&message);
                DispatchMessage(&message);
            }
    }
    return message.wParam;
}

Answer 1

编程语言不像数学那样工作。在数学中，你可以说 x = y；然后说 y = 5；然后你可以推断 x 一定是 5。

然而，在编程语言中，当你说HWND hwndParent = window;时然后hwndParent取值 window 在分配时，所以如果您稍后实际初始化 window与 window = ...您不能期望 hwndParent 的值突然变得有意义。它将保持未初始化状态，因为 window在分配时尚未初始化。

提示:如果您能够做到HWND hwndParent = window;当window未初始化，这意味着您没有收到任何警告。这又意味着您没有将编译器配置为在执行此类操作时发出警告。不要在没有警告的情况下尝试编程。这样你永远不会取得多大成就。