通过web api发出返回图像

Question

我有一个奇怪的问题,通过web api返回一个图像,我在我的应用程序中的几个地方这样做,但没有失败,但这一个导致我的问题,任何帮助将非常感激.

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);
        }

我真的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,但出于某种原因,当我在内存中执行此操作时,结果是一个0字节的空文件,我尝试手动设置内容长度但是文件没有完全下载.

Answer 1

保存发生后,您需要重置流的位置.

bitmapStream.Position = 0;