20 tips for ASP. net mvc 3 development (12) [20 recipes for programming MVC 3]: Scaling image sizes to create thumbnails

Topics

Most of the images uploaded by users to the website are large-sized photos. Generally, the website displays thumbnails of these images or photos before users want to see the complete images.

Solution

Use the following classes to adjust the width and height of the uploaded image files: filestream, image, bitmap, and graphics.

Discussion

In the following example, the previously created fileupload class is modified and reorganized. Create a new method called "resizeimage" to resize the image. The adjusted image file will be saved to the "thumbnails" sub-folder in the source file storage folder. You also need to modify the deletefile method to add and delete both the original image and thumbnail, and to avoid duplicationCodeCreate a method for deleting a function. The following shows the class code of the changed part:

 Using System;
 Using System. Collections. Generic;
 Using System. LINQ;
Using System. Web;
 Using System. IO;
 Using System. drawing;
 Using System. Drawing. drawing2d;
 Namespace Mvcapplication4.utils
{
 Public   Static   Class Fileupload
{
 Public   Static   Char Dirseparator =
System. Io. Path. directoryseparatorchar;
 Public   Static   String Filespath = "  Content  " +
Dirseparator + "  Uploads  " + Dirseparator;
 Public   Static   String Uploadfile (httppostedfilebase file)
{
...
 //  Save thumbnail  
 Resizeimage (file, 150 , 100 );
...
}
 Public   Static   Void Deletefile ( String Filename)
{
 // If no file name is specified, nothing will be done.  
              If (Filename. Length = 0 ) Return ;
 //  Set the deletion path  
              String Path = filespath + dirseparator + filename;
 String Thumbpath = filespath + dirseparator +
 "  Thumbnails  " + Dirseparator + filename;
Removefile (PATH );
Removefile (thumbpath );
}
 Private   Static   Void Removefile ( String Path)
{
 //  Check whether the file exists  
              If (File. exists (path. getfullpath (PATH )))
{
 // Delete an object  
 File. Delete (path. getfullpath (PATH ));
}
}
 Public   Static   Void Resizeimage (httppostedfilebase file,
 Int Width, Int Height)
{
 String Thumbnaildirectory =
String. Format ( @" {0} {1} {2}  " , Filespath,
Dirseparator, "  Thumbnails  " );
 //  Check whether the target folder exists  
              If (! Directory. exists (thumbnaildirectory ))
{
 //  Create a folder if it does not exist.  
 Directory. createdirectory (thumbnaildirectory );
}
 //  Set the path for saving thumbnails  
              String ImagePath =
String. Format ( @"  {0} {1} {2}  " , Thumbnaildirectory,
Dirseparator, file. filename );
 //  Save the file stream to the disk  
 Filestream stream = New Filestream (path. getfullpath (
ImagePath), filemode. openorcreate );
 //  Zooming uploaded files  
 Image origimage = image. fromstream (file. inputstream );
 //  Create a thumbnail object  
 Bitmap tempbitmap = New Bitmap (width, height );
 //  Create thumbnail image quality  
 Graphics newimage = graphics. fromimage (tempbitmap );
Newimage. compositingquality =
Compositingquality. highquality;
Newimage. smoothingmode =
Smoothingmode. highquality;
Newimage. interpolationmode =
Interpolationmode. highqualitybicubic;
 //  Create a rectangle object to draw  
 Rectangle imagerectangle = New Rectangle ( 0 , 0 ,
Width, height );
Newimage. drawimage (origimage, imagerectangle );
 //  Save thumbnail  
 Tempbitmap. Save (stream, origimage. rawformat );
 //  Release resources  
 Newimage. Dispose ();
Tempbitmap. Dispose ();
Origimage. Dispose ();
Stream. Close ();
Stream. Dispose ();
}
}
}

In the above example, We made many modifications, especially the resizeimage method. First, determine whether the "thumbnails" folder exists and the Creation function. Next, a new filestream object is created and the edited image is saved to the "thumbnails" folder.

Create the original image object from the submitted inputstream. Then, a bitmap Bitmap bitmap instance is created based on the size of the thumbnail. Create a new graphics object based on this bitmap object, and set the image quality, smoothness, and interpolation mode. If these values are not set, thumbnails are difficult to see due to pixel and proportional deformation.

After setting these values, create a recangle object of the original size and scale the object to the previously created graphics object. Then, adjust the size. Finally, save the bitmap object and release all resources.

Reference

Filestream image bitmap graphics original book Address Book source code