在C/C++中，可以有以下两种办法
使用COM接口IThumbnailCache
文档链接：https://learn.microsoft.com/en-us/windows/win32/api/thumbcache/nn-thumbcache-ithumbnailcache
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DeleteObjectDeleteObject(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：https://learn.microsoft.com/en-us/windows/win32/api/shobjidl_core/nn-shobjidl_core-ishellitemimagefactory
官方示例代码：https://github.com/microsoft/Windows-classic-samples/blob/main/Samples/Win7Samples/winui/shell/appplatform/UsingImageFactory/ImageFactorySample.cpp
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DeleteObjectDeleteObject(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;