如何从菜单打开图像并在 win 32 程序上显示？

Question

我创建了一个简单的 win32 应用程序来从菜单打开对话框，select 位图图像并在 window 上显示或绘制它。现在我面临的问题是，当我从 GetOpenFileName 方法获取文件名并将其传递给 LoadImage 函数时，无法加载图像。但是如果我将文件路径 "D:/Splash.bmp" 直接传递给函数参数，图像就会被加载。问题是 GetOpenFileName 方法在程序使用 "D:/Splash.bmp" 时将 "D:\Splash.bmp" 作为路径。可能是什么错误？

代码如下：

//Win32Bitmap.cpp : Defines the entry point for the application.//

#include "stdafx.h"
#include "Win32Bitmap.h"
#include<Windows.h>
#include <Commdlg.h>

#define MAX_LOADSTRING 100

// Global Variables:
HINSTANCE hInst;                                // current instance
TCHAR szTitle[MAX_LOADSTRING];                  // The title bar text
TCHAR szWindowClass[MAX_LOADSTRING];            // the main window class name

// Forward declarations of functions included in this code module:
ATOM                MyRegisterClass(HINSTANCE hInstance);
BOOL                InitInstance(HINSTANCE, int);
LRESULT CALLBACK    WndProc(HWND, UINT, WPARAM, LPARAM);
INT_PTR CALLBACK    About(HWND, UINT, WPARAM, LPARAM);

int APIENTRY _tWinMain(_In_ HINSTANCE hInstance,
                 _In_opt_ HINSTANCE hPrevInstance,
                 _In_ LPTSTR    lpCmdLine,
                 _In_ int       nCmdShow)
{
UNREFERENCED_PARAMETER(hPrevInstance);
UNREFERENCED_PARAMETER(lpCmdLine);

// TODO: Place code here.
MSG msg;
HACCEL hAccelTable;

// Initialize global strings
LoadString(hInstance, IDS_APP_TITLE, szTitle, MAX_LOADSTRING);
LoadString(hInstance, IDC_WIN32BITMAP, szWindowClass, MAX_LOADSTRING);
MyRegisterClass(hInstance);

// Perform application initialization:
if (!InitInstance (hInstance, nCmdShow))
{
    return FALSE;
}

hAccelTable = LoadAccelerators(hInstance, MAKEINTRESOURCE(IDC_WIN32BITMAP));

// Main message loop:
while (GetMessage(&msg, NULL, 0, 0))
{
    if (!TranslateAccelerator(msg.hwnd, hAccelTable, &msg))
    {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }
}

return (int) msg.wParam;
}



//
//  FUNCTION: MyRegisterClass()
//
//  PURPOSE: Registers the window class.
//
ATOM MyRegisterClass(HINSTANCE hInstance)
{
WNDCLASSEX wcex;

wcex.cbSize = sizeof(WNDCLASSEX);

wcex.style          = CS_HREDRAW | CS_VREDRAW;
wcex.lpfnWndProc    = WndProc;
wcex.cbClsExtra     = 0;
wcex.cbWndExtra     = 0;
wcex.hInstance      = hInstance;
wcex.hIcon          = LoadIcon(hInstance, MAKEINTRESOURCE(IDI_WIN32BITMAP));
wcex.hCursor        = LoadCursor(NULL, IDC_ARROW);
wcex.hbrBackground  = (HBRUSH)(COLOR_WINDOW+1);
wcex.lpszMenuName   = MAKEINTRESOURCE(IDC_WIN32BITMAP);
wcex.lpszClassName  = szWindowClass;
wcex.hIconSm        = LoadIcon(wcex.hInstance, MAKEINTRESOURCE(IDI_SMALL));

return RegisterClassEx(&wcex);
}

//
//   FUNCTION: InitInstance(HINSTANCE, int)
//
//   PURPOSE: Saves instance handle and creates main window
//
//   COMMENTS:
//
//        In this function, we save the instance handle in a global variable      and
//        create and display the main program window.
//
BOOL InitInstance(HINSTANCE hInstance, int nCmdShow)
{
HWND hWnd;

hInst = hInstance; // Store instance handle in our global variable

hWnd = CreateWindow(szWindowClass, szTitle, WS_OVERLAPPEDWINDOW,
  CW_USEDEFAULT, 0, CW_USEDEFAULT, 0, NULL, NULL, hInstance, NULL);

if (!hWnd)
{
   return FALSE;
}

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

return TRUE;
}
bool LoadAndBlitBitmap(LPTSTR szFileName, HDC hdcWin)
{
    HBITMAP hbitmap;
hbitmap = (HBITMAP)LoadImage(NULL, szFileName, IMAGE_BITMAP, 0, 0,  LR_LOADFROMFILE);
if (hbitmap == NULL)
{
    MessageBox(NULL, L"Image couldn't be loaded", L"Error", MB_OK | MB_ICONEXCLAMATION);
    return false;
}

//create a memory device context that is compatible with the window
HDC hdclocal = CreateCompatibleDC(hdcWin);
if (hdclocal == NULL)
{
    MessageBox(NULL, L"device context not created", L"Error", MB_OK | MB_ICONEXCLAMATION);
    return false;
}

//get the bitmap's parameters and verify the get
BITMAP qbitmap;
int ireturn = GetObject(reinterpret_cast<HGDIOBJ>(hbitmap), sizeof(BITMAP), reinterpret_cast<LPVOID>(&qbitmap));
if (!ireturn)
{
    MessageBox(NULL, L"Get object failed", L"Error", MB_OK | MB_ICONEXCLAMATION);
    return false;
}

//select the loaded bitmap into the device context
HBITMAP holdbitmap = (HBITMAP)SelectObject(hdclocal, hbitmap);
if (holdbitmap==NULL)
{
    MessageBox(NULL, L"Get object failed", L"Error", MB_OK | MB_ICONEXCLAMATION);
    return false;
}

//transfer the device context from the memory device context to the windows context(actual drawing surface)
bool qRetBlit = BitBlt(hdcWin, 0, 0, qbitmap.bmWidth, qbitmap.bmHeight, hdclocal, 0, 0, SRCCOPY);
if (!qRetBlit)
{
    MessageBox(NULL, L"bitblt failed", L"Error", MB_OK | MB_ICONEXCLAMATION);
    return false;
}

//deallocate the resources

SelectObject(hdclocal, holdbitmap);
DeleteDC(hdclocal);
DeleteObject(hbitmap);
return true;
}


//
//  FUNCTION: WndProc(HWND, UINT, WPARAM, LPARAM)
//
//  PURPOSE:  Processes messages for the main window.
//
//  WM_COMMAND  - process the application menu
//  WM_PAINT    - Paint the main window
//  WM_DESTROY  - post a quit message and return
//
//
LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM  lParam)
{
int wmId, wmEvent;
PAINTSTRUCT ps;
HDC hdc;
wchar_t szFileName[MAX_PATH] = L"";
switch (message)
{
case WM_COMMAND:
    wmId    = LOWORD(wParam);
    wmEvent = HIWORD(wParam);
    // Parse the menu selections:
    switch (wmId)
    {
    case IDM_ABOUT:
        DialogBox(hInst, MAKEINTRESOURCE(IDD_ABOUTBOX), hWnd, About);
        break;
    case IDM_EXIT:
        DestroyWindow(hWnd);
        break;
    case ID_FILE_OPEN:
    {
        OPENFILENAME ofn;

        ZeroMemory(&ofn, sizeof(ofn));
        ofn.lStructSize = sizeof(ofn); // SEE NOTE BELOW
        ofn.hwndOwner = hWnd;
        ofn.lpstrFilter = L"Bitmap Files (*.bmp)[=10=]*.bmp[=10=]All Files (*.*)[=10=]*.*[=10=]";
        ofn.lpstrFile = szFileName;
        ofn.nMaxFile = MAX_PATH;
        ofn.Flags = OFN_EXPLORER | OFN_FILEMUSTEXIST | OFN_HIDEREADONLY;
        ofn.lpstrDefExt = L"bmp";
        if (GetOpenFileName(&ofn))
        {
            MessageBox(NULL, szFileName, L"path", MB_OK);
            //InvalidateRect(hWnd, 0, TRUE);
        }
    }
    break;
    default:
        return DefWindowProc(hWnd, message, wParam, lParam);
    }
    break;
case WM_PAINT:
    hdc = BeginPaint(hWnd, &ps);
    // TODO: Add any drawing code here...

        LoadAndBlitBitmap(L"D:/Splash.bmp", hdc);


    EndPaint(hWnd, &ps);
    break;
case WM_DESTROY:
    PostQuitMessage(0);
    break;
default:
    return DefWindowProc(hWnd, message, wParam, lParam);
}
return 0;
}

// Message handler for about box.
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;
}

Answer 1

反斜杠不是问题所在。事实上，windows 比正斜杠更喜欢反斜杠。您的问题是您已将 szFileName 缓冲区设为 window 过程函数 (WndProc) 的本地缓冲区。当您单击 select 文件的菜单项时，消息 WM_COMMAND 将发送到 window 并由其 window 过程处理。您已正确实现打开对话框和检索文件路径。但是，当此处理完成时，函数 WndProc 退出并销毁堆栈中的所有局部变量，包括 szFileName.

中包含的文件路径

要解决您的问题，请将 szFileName 设为全局变量，这样它就不会被破坏。另请注意，window 不会在您 select 图像文件后自动更新自身，您需要通过在调用 [=17= 之后添加此代码来指示 window 重新绘制自身]:

InvalidateRect(hWnd, NULL, TRUE);
UpdateWindow(hWnd);

这将使整个 window 区域无效并安排重新绘制 window（这意味着消息 WM_PAINT 将再次发送到 window 并由WndProc).

如何从菜单打开图像并在 win 32 程序上显示？

How to open an image from menu and display on win 32 program?

windows

winapi

win32gui

loadimage