如何获取文件缩略图(C#和C++实现)

在C++中，可以有以下两种办法

使用COM接口IThumbnailCache

文档链接：IThumbnailCache (thumbcache.h) - Win32 apps | Microsoft Learn

示例代码如下：

VOID GetFileThumbnail(PCWSTR path)
{
    HRESULT hr = CoInitialize(nullptr);

    IShellItem* item = nullptr;
    hr = SHCreateItemFromParsingName(path, nullptr, IID_PPV_ARGS(&item));

    IThumbnailCache* cache = nullptr;
    hr = CoCreateInstance(
        CLSID_LocalThumbnailCache,
        nullptr,
        CLSCTX_INPROC,
        IID_PPV_ARGS(&cache));

    WTS_CACHEFLAGS flags = WTS_LOWQUALITY;
    ISharedBitmap* shared_bitmap;
    hr = cache->GetThumbnail(
        item,
        12*16,
        WTS_EXTRACT,
        &shared_bitmap,
        nullptr,
        nullptr);

    HBITMAP hbitmap = NULL;
    hr = shared_bitmap->GetSharedBitmap(&hbitmap);
    shared_bitmap->Release();
    cache->Release();
    CoUninitialize();

    //使用hbitmap，使用完成后调用DeleteObject
    DeleteObject(hbitmap);

}

前面我一直使用的这种方式，但是最近系统升级后，会报 Generic Error in GDI+ 

后面我升级成了下面这种方式

使用IShellItemImageFactory接口

文档链接：IShellItemImageFactory (shobjidl_core.h) - Win32 apps | Microsoft Learn

官方示例代码：Windows-classic-samples/Samples/Win7Samples/winui/shell/appplatform/UsingImageFactory/ImageFactorySample.cpp at main · microsoft/Windows-classic-samples · GitHub

HRESULT hr = CoInitializeEx(NULL, COINIT_APARTMENTTHREADED | COINIT_DISABLE_OLE1DDE);
    HBITMAP hbmp = NULL;

    if (SUCCEEDED(hr))
    {
        IShellItemImageFactory* pImageFactory;
        hr = SHCreateItemFromParsingName(path, NULL, IID_PPV_ARGS(&pImageFactory));
        if (SUCCEEDED(hr))
        {
            SIZE size = { 256, 256 };  //图像大小
            hr = pImageFactory->GetImage(size, SIIGBF_THUMBNAILONLY, &hbmp);
            pImageFactory->Release();
        }
        CoUninitialize();

        //使用hbmp,使用完成后调用DeleteObject
        DeleteObject(hbmp);
    }

在C#中使用，可以直接nuget引用  WindowsAPICodePack-Shell  包

PM> NuGet\Install-Package WindowsAPICodePack-Shell -Version 1.1.1

然后用下面的代码就可以获取文件缩略图

ShellFile shellFile = ShellFile.FromFilePath(filepath);
Bitmap shellThumb = shellFile.Thumbnail.ExtraLargeBitmap;