如何在ASP.NET C#中使用MultipleFileUpload减少图像文件，调整大小而不损失质量

Question

我正在使用MultipleFileUpload上传多张照片，如果我要上传大尺寸的图像，那么滑块中的图像不是固定大小的，不会显示出正确的外观。上传时间限制画廊图片的大小时，有什么代码吗。

下面是我的c#代码：

protected void lnkbtn_Submit_Click(object sender, EventArgs e)
{
    try
    {
        if (MultipleFileUpload.HasFiles)
        {
            int MaxGalleryId, ReturnValue;
            ReturnValue = obj.fnCreateNewPhotoGallery(txtGalleryName.Text, txtGalleryDescrption.Text, DateTime.Now, out MaxGalleryId);
            if (ReturnValue != 0)
            {
                string GalleryPath = System.Configuration.ConfigurationManager.AppSettings["GalleryPath"] + MaxGalleryId;
                Directory.CreateDirectory(Server.MapPath(GalleryPath));
                string ThumbnailPath = System.Configuration.ConfigurationManager.AppSettings["ThumbnailPath"] + MaxGalleryId;
                Directory.CreateDirectory(Server.MapPath(ThumbnailPath));
                StringBuilder UploadedFileNames = new StringBuilder();
                foreach (HttpPostedFile uploadedFile in MultipleFileUpload.PostedFiles)
                {
                    //Upload file
                    string FileName = HttpUtility.HtmlEncode(Path.GetFileName(uploadedFile.FileName));
                    string SaveAsImage = System.IO.Path.Combine(Server.MapPath(GalleryPath + "/"), FileName);
                    uploadedFile.SaveAs(SaveAsImage);
                    //Create thumbnail for uploaded file and save thumbnail on disk
                    Bitmap Thumbnail = CreateThumbnail(SaveAsImage, 200, 200);
                    string SaveAsThumbnail = System.IO.Path.Combine(Server.MapPath(ThumbnailPath + "/"), FileName);
                    Thumbnail.Save(SaveAsThumbnail);
                }
                HTMLHelper.jsAlertAndRedirect(this, "Gallery created successfully. ", "Album.aspx?GalleryId=" + MaxGalleryId);
            }
        }
    }
    catch
    {
        HTMLHelper.jsAlertAndRedirect(this, "Gallery is not created. Some exception occured ", "CreateAlbum.aspx");
    }
}

下面是我的创建缩略图方法代码：

public Bitmap CreateThumbnail(string ImagePath, int ThumbnailWidth, int ThumbnailHeight)
{
    System.Drawing.Bitmap Thumbnail = null;
    try
    {
        Bitmap ImageBMP = new Bitmap(ImagePath);
        ImageFormat loFormat = ImageBMP.RawFormat;
        decimal lengthRatio;
        int ThumbnailNewWidth = 0;
        int ThumbnailNewHeight = 0;
        decimal ThumbnailRatioWidth;
        decimal ThumbnailRatioHeight;
        // If the uploaded image is smaller than a thumbnail size the just return it
        if (ImageBMP.Width <= ThumbnailWidth && ImageBMP.Height <= ThumbnailHeight)
            return ImageBMP;
        // Compute best ratio to scale entire image based on larger dimension.
        if (ImageBMP.Width > ImageBMP.Height)
        {
            ThumbnailRatioWidth = (decimal)ThumbnailWidth / ImageBMP.Width;
            ThumbnailRatioHeight = (decimal)ThumbnailHeight / ImageBMP.Height;
            lengthRatio = Math.Min(ThumbnailRatioWidth, ThumbnailRatioHeight);
            ThumbnailNewWidth = ThumbnailWidth;
            decimal lengthTemp = ImageBMP.Height * lengthRatio;
            ThumbnailNewHeight = (int)lengthTemp;
        }
        else
        {
            ThumbnailRatioWidth = (decimal)ThumbnailWidth / ImageBMP.Width;
            ThumbnailRatioHeight = (decimal)ThumbnailHeight / ImageBMP.Height;
            lengthRatio = Math.Min(ThumbnailRatioWidth, ThumbnailRatioHeight);
            ThumbnailNewHeight = ThumbnailHeight;
            decimal lengthTemp = ImageBMP.Width * lengthRatio;
            ThumbnailNewWidth = (int)lengthTemp;
        }
        Thumbnail = new Bitmap(ThumbnailNewWidth, ThumbnailNewHeight);
        Graphics g = Graphics.FromImage(Thumbnail);
        g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
        g.FillRectangle(Brushes.White, 0, 0, ThumbnailNewWidth, ThumbnailNewHeight);
        g.DrawImage(ImageBMP, 0, 0, ThumbnailNewWidth, ThumbnailNewHeight);
        ImageBMP.Dispose();
    }
    catch
    {
        return null;
    }
    return Thumbnail;
}

上面的代码有一个命令行//从那里上传文件上传图像。我在画廊中使用了这个例子：http://www.bugdebugzone.com/2013/10/create-dynamic-image-gallery-slideshow.html

Answer 1

您可以将uploadedFile的ContentLength属性设置为：

if (uploadedFile.ContentLength > 1000000)
{
    continue;
}

ContentLength是已上载文件的大小（以字节为单位）。https://msdn.microsoft.com/en-us/library/system.web.httppostedfile.contentlength（v=vs.110）.aspx