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How To Validate File Uploader Server Side In ASP.NET

Introduction

In this blog, I will demonstrate how to validate file upload server side in asp.net.

Step 1

Create an empty ASP.net web application in Visual Studio 2015 or the version of your choice.

Step 2

Right click on the project and add web form and give it a meaningful name.

Step 3

Add the following Bootstrap script and styles cdn link in head section

  1. <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.1.0/css/bootstrap.min.css">  
  2. <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>  
  3. <script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.1.0/js/bootstrap.min.js"></script>  

Step 4

Design web form using file upload control, button control, and bootstrap.

  1. <body>  
  2.     <form id="form1" runat="server">  
  3.         <div class="container py-5">  
  4.             <h4 class="text-center text-uppercase">How to validate file uploader server side in ASP.NET</h4>  
  5.             <div class="row">  
  6.                 <div class="col-sm-6 col-md-6 col-xs-12">  
  7.                     <div class="form-group">  
  8.                         <label>Choose File:</label>  
  9.                         <div class="input-group">  
  10.                             <div class="custom-file">  
  11.                                 <asp:FileUpload ID="FileUpload1" runat="server" CssClass="custom-file-input" />  
  12.                                 <label class="custom-file-label"></label>  
  13.                             </div>  
  14.                             <div class="input-group-append">  
  15.                                 <asp:Button ID="btnUpload" runat="server" Text="Upload" CssClass="btn btn-secondary" OnClick="btnUpload_Click" />  
  16.                             </div>  
  17.                         </div>  
  18.                         <asp:Label ID="lblMessage" runat="server"></asp:Label>  
  19.                     </div>  
  20.                 </div>  
  21.             </div>  
  22.         </div>  
  23.     </form>  
  24. </body  

Step 5

Right click on project, and create image folder to upload image.

Step 6

Double click on upload button and write the following code

  1. protected void btnUpload_Click(object sender, EventArgs e)  
  2.      {  
  3.          if (FileUpload1.HasFile)  
  4.          {  
  5.              string fileExtwnsion = Path.GetExtension(FileUpload1.FileName);  
  6.   
  7.              if (fileExtwnsion.ToLower()!=".jpg" && fileExtwnsion.ToLower()!=".png")  
  8.              {  
  9.                  lblMessage.Text = "Only jpg and png file allowed";  
  10.                  lblMessage.ForeColor = System.Drawing.Color.Red;  
  11.              }  
  12.              else  
  13.              {  
  14.                  int fileSize = FileUpload1.PostedFile.ContentLength;  
  15.                  if (fileSize> 2097152)  
  16.                  {  
  17.                      lblMessage.Text = "Maximum size 2(MB) exceeded ";  
  18.                      lblMessage.ForeColor = System.Drawing.Color.Red;  
  19.                  }  
  20.                  else  
  21.                  {  
  22.                      FileUpload1.SaveAs(Server.MapPath("~/images/" + FileUpload1.FileName));  
  23.                      lblMessage.Text = "File Uploaded successfully";  
  24.                      lblMessage.ForeColor = System.Drawing.Color.Green;  
  25.                  }  
  26.              }   
  27.          }  
  28.          else  
  29.          {  
  30.              lblMessage.Text = "File not uploaded";  
  31.              lblMessage.ForeColor = System.Drawing.Color.Red;  
  32.          }  
  33.      }  

Step 7

Run project ctrl F5

Screenshot 1

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Screenshot 2
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Screenshot 3
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