.NET Image Uploading

• Download source - netimageupload.zip (2.4 Kb)

Uploading images via .NET

Previously, adding the ability to upload images via ASP (with sizing, thumbnail features, etc.) would have required the use of an external component. With the advent of .NET, the ability to handle images can be done easily and freely through the use of the Bitmap and Image classes.

In this tutorial, we will be going through the steps of creating a simple web form in which you can upload an image file, and the form will verify whether it’s a JPEG file, whether there are duplicate files already (and rename your uploaded file if necessary), and create a thumbnail of the file uploaded.

This tutorial already assumes a basic knowledge of .NET Web Forms and C#.

By the way, some credit goes to Konstantin Vasserman for his code on uploading. If you need to upload the image into a DB, then look at his article.

1. Create a new web application project.
   
   
2. Open up the web form.
   
   
3. Add a File field from the HTML tab onto your form, and convert it into a server control. In this example, the file field will be named filUpload.
   (To convert any HTML tag into a server control, right click on it and select Run As Server Control.)
   
   
4. Switch to HTML view and add/alter the enctype attribute of the form tag to multipart/form-data.
   Example: enctype="multipart/form-data"
   
   
5. Add a Web Form Button onto the form, and name it btnUpload.
   
   
6. Add a folder called /images to the web application.
   
   
7. Add a Web Form Image onto the form, and name it imgPicture. Adjust the width to 160 and height to 120.
   
   
8. Add a Label called lblOutput. This will return any errors if the upload happens to fail.
   
   
9. In the btnUpload Click event, add the following code.
   (If you want to analyze the code in detail below, it's better to copy and paste into the VS.NET IDE since some of the lines are long.)
   
   C#

   private void btnUpload_Click(object sender, System.EventArgs e)
   {
       // Initialize variables
       string sSavePath;
       string sThumbExtension;
       int intThumbWidth;
       int intThumbHeight;
   
       // Set constant values
       sSavePath = "images/";
       sThumbExtension = "_thumb";
       intThumbWidth = 160;
       intThumbHeight = 120;
   
       // If file field isn’t empty
       if (filUpload.PostedFile != null)
       {
           // Check file size (mustn’t be 0)
           HttpPostedFile myFile = filUpload.PostedFile;
           int nFileLen = myFile.ContentLength;
           if (nFileLen == 0)
           {
               lblOutput.Text = "No file was uploaded.";
               return;
           }
   
           // Check file extension (must be JPG)
           if (System.IO.Path.GetExtension(myFile.FileName).ToLower() != ".jpg")
           {
               lblOutput.Text = "The file must have an extension of JPG";
               return;
           }
   
           // Read file into a data stream
           byte[] myData = new Byte[nFileLen];
           myFile.InputStream.Read(myData,0,nFileLen);
   
           // Make sure a duplicate file doesn’t exist.  If it does, keep on appending an 
           // incremental numeric until it is unique
           string sFilename = System.IO.Path.GetFileName(myFile.FileName);
           int file_append = 0;
           while (System.IO.File.Exists(Server.MapPath(sSavePath + sFilename)))
           {
               file_append++;
               sFilename = System.IO.Path.GetFileNameWithoutExtension(myFile.FileName)
                                + file_append.ToString() + ".jpg";
           }
   
           // Save the stream to disk
           System.IO.FileStream newFile
                   = new System.IO.FileStream(Server.MapPath(sSavePath + sFilename), 
                                              System.IO.FileMode.Create);
           newFile.Write(myData,0, myData.Length);
           newFile.Close();
   
           // Check whether the file is really a JPEG by opening it
           System.Drawing.Image.GetThumbnailImageAbort myCallBack = 
                          new System.Drawing.Image.GetThumbnailImageAbort(ThumbnailCallback);
           Bitmap myBitmap;
           try
           {
               myBitmap = new Bitmap(Server.MapPath(sSavePath + sFilename));
   
               // If jpg file is a jpeg, create a thumbnail filename that is unique.
               file_append = 0;
               string sThumbFile = System.IO.Path.GetFileNameWithoutExtension(myFile.FileName)
                                                        + sThumbExtension + ".jpg";
               while (System.IO.File.Exists(Server.MapPath(sSavePath + sThumbFile)))
               {
                   file_append++;
                   sThumbFile = System.IO.Path.GetFileNameWithoutExtension(myFile.FileName) + 
                                  file_append.ToString() + sThumbExtension + ".jpg";
               }
   
               // Save thumbnail and output it onto the webpage
               System.Drawing.Image myThumbnail
                       = myBitmap.GetThumbnailImage(intThumbWidth, 
                                                    intThumbHeight, myCallBack, IntPtr.Zero);
               myThumbnail.Save (Server.MapPath(sSavePath + sThumbFile));
               imgPicture.ImageUrl = sSavePath + sThumbFile;
   
               // Displaying success information
               lblOutput.Text = "File uploaded successfully!";
   
               // Destroy objects
               myThumbnail.Dispose();
               myBitmap.Dispose();
           }
           catch (ArgumentException errArgument)
           {
               // The file wasn't a valid jpg file
               lblOutput.Text = "The file wasn't a valid jpg file.";
               System.IO.File.Delete(Server.MapPath(sSavePath + sFilename));
           }
       }
   }
   
   public bool ThumbnailCallback()
   {
       return false;
   }        

10. Run the webpage, and test with JPG files and other files to test the error-checking mechanism.
    
    
11. If you have any problems/suggestions, please leave a message below. :-)