c# - 通过 Web api 返回图像的问题

Question

我在通过 Web api 返回图像时遇到了一个奇怪的问题，我在应用程序中的多个地方都执行了此操作，但没有失败，但这一个导致了我的问题，任何帮助将不胜感激。

这有效

  Bitmap bitmap = getImage();
        MemoryStream bitmapStream = new MemoryStream();
        bitmap.Save("C:\\test.png", System.Drawing.Imaging.ImageFormat.Png);

        if (bitmap != null)
        {
            if (Request.Headers.IfModifiedSince.HasValue)
            {
                // The file has not been modified since the browser cached it.
                return new HttpResponseMessage(HttpStatusCode.NotModified);
            }
            HttpResponseMessage response = new HttpResponseMessage(HttpStatusCode.OK);
            response.Content = new StreamContent(new FileStream("C:\\test.png", FileMode.Open));
            response.Content.Headers.ContentType = new MediaTypeHeaderValue("image/png");
            return response;
        }
        else
        {
            return new HttpResponseMessage(HttpStatusCode.NotFound);
        }

虽然这不是

 Bitmap bitmap = getImage();
        MemoryStream bitmapStream = new MemoryStream();
        bitmap.Save(bitmapStream, System.Drawing.Imaging.ImageFormat.Png);

        if (bitmap != null)
        {
            if (Request.Headers.IfModifiedSince.HasValue)
            {
                // The file has not been modified since the browser cached it.
                return new HttpResponseMessage(HttpStatusCode.NotModified);
            }
            HttpResponseMessage response = new HttpResponseMessage(HttpStatusCode.OK);
            response.Content = new StreamContent(bitmapStream);
            response.Content.Headers.ContentType = new MediaTypeHeaderValue("image/png");
            return response;
        }
        else
        {
            return new HttpResponseMessage(HttpStatusCode.NotFound);
        }

我确实需要在内存中执行此操作，而不是将临时文件保存到驱动器中，但由于某种原因，当我在内存中执行此操作时，结果是一个空文件 0 字节，我确实尝试手动设置内容长度，但随后该文件根本无法下载。

Answer 1

保存后您需要重置流的位置。

bitmapStream.Position = 0;