c++ - 如何在窗口 MFC 应用程序中更改图像

Question

首先让我说我对 MFC 应用程序很陌生，所以请多多包涵...

我想创建一个带有图像的窗口(比如绿灯)。必要时，我希望应用程序更改图像(更改为黄灯或红灯)。我有创建窗口并显示图像(绿灯)的代码，但它不会更新图像(当 i == 15 或 i == 50 时)

#include "resource.h"

using namespace std;

const char g_szClassName[] = "myWindowClass";

HBITMAP Light = NULL;

// Step 4: the Window Procedure
LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
    switch (msg)
    {
    case WM_PAINT: 
        {   
            BITMAP bm;
            PAINTSTRUCT ps;

            HDC hdc = BeginPaint(hwnd, &ps);

            HDC hdcMem = CreateCompatibleDC(hdc);
            HBITMAP hbmOld = (HBITMAP)SelectObject(hdcMem, Light);

            GetObject(Light, sizeof(bm), &bm);

            BitBlt(hdc, 20, 180, bm.bmWidth, bm.bmHeight, hdcMem, 0, 0, SRCCOPY);

            SelectObject(hdcMem, hbmOld);
            DeleteDC(hdcMem);

            EndPaint(hwnd, &ps);
        }
    case WM_CREATE:
        {
            Light = LoadBitmap(GetModuleHandle(NULL), MAKEINTRESOURCE(IDB_BITMAP1));
        }
        break;
    case WM_COMMAND:
        switch (LOWORD(wParam))
        {

        }
        break; 
    case WM_CLOSE:
        DestroyWindow(hwnd);
        break;
    case WM_DESTROY:
    {
        DeleteObject(Light);
        PostQuitMessage(0);
    }
        break;
    default:
        return DefWindowProc(hwnd, msg, wParam, lParam);
    }
    return 0;
}

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
    LPSTR lpCmdLine, int nCmdShow)
{
    WNDCLASSEX wc;
    HWND hwnd;
    MSG Msg;
    int eventCode;

    int i = 0;

    wc.cbSize = sizeof(WNDCLASSEX);
    wc.style = 0;
    wc.lpfnWndProc = WndProc;
    wc.cbClsExtra = 0;
    wc.cbWndExtra = 0;
    wc.hInstance = hInstance;
    wc.hIcon = LoadIcon(NULL, IDI_APPLICATION);
    wc.hCursor = LoadCursor(NULL, IDC_ARROW);
    wc.hbrBackground = (HBRUSH)(COLOR_WINDOW + 1);
    wc.lpszMenuName = NULL;
    wc.lpszClassName = (LPCSTR)g_szClassName;
    wc.hIconSm = LoadIcon(NULL, IDI_APPLICATION);

    if (!RegisterClassEx(&wc))
    {
        MessageBox(NULL, (LPCSTR)"Window Registration Failed!", (LPCSTR)"Error!",
            MB_ICONEXCLAMATION | MB_OK);
        return 0;
    }

    // Step 2: Creating the Window
    hwnd = CreateWindowEx(
        WS_EX_CLIENTEDGE,
        (LPCSTR)g_szClassName,
        (LPCSTR)"Test Picture",
        WS_OVERLAPPEDWINDOW,
        CW_USEDEFAULT, CW_USEDEFAULT, 420, 280,
        NULL, NULL, hInstance, NULL);

    if (hwnd == NULL)
    {
        MessageBox(NULL, (LPCSTR)"Window Creation Failed!", (LPCSTR)"Error!",
            MB_ICONEXCLAMATION | MB_OK);
        return 0;
    }

    ShowWindow(hwnd, nCmdShow);
    UpdateWindow(hwnd);

    // Step 3: The Message Loop
    while (GetMessage(&Msg, NULL, 0, 0) > 0)
    {
        TranslateMessage(&Msg);
        DispatchMessage(&Msg);

        if (i == 15)
        {
            Light = LoadBitmap(GetModuleHandle(NULL), MAKEINTRESOURCE(IDB_BITMAP3));
            UpdateWindow(hwnd);
        }
        else if (i == 50)
        {
            Light = LoadBitmap(GetModuleHandle(NULL), MAKEINTRESOURCE(IDB_BITMAP2));
            UpdateWindow(hwnd);
        }
        i++;
    }

    return Msg.wParam;
}

我以为我能做到

Light = LoadBitmap(GetModuleHandle(NULL), MAKEINTRESOURCE(IDB_BITMAP3));
UpdateWindow(hwnd);

更新窗口图片，但我错了:( ...我可以用什么来更改图像？

Answer 1

您需要调用 InvalidateRect 来引起重绘。如果窗口的无效区域为空，则 UpdateWindow 不执行任何操作。