Custom Validator for FileUpload in asp.net 2.0

Validation Web controls are ASP.NET 2.0 Web controls designed to validate form fields control inputs with some rules apply to it. Previously it used to achieve with the javascript/vbscripts functions on user controls like text box and drop down list. it was bit annoying and time consuming and also code grows to longer line which is difficult to manage.

asp.net 2.0 introduces new validation controls to resolve these issues. One of which I am discussing here,

CustomValidator- Checks the form field's value against custom validation logic that you, the developer, provide with the help of client script written in javascript.

javascript function

       function check_ClientValidate(source, args)
           {
             var _pageStatus = true;
             if(args.Value != "")
               { _pageStatus = true;}
             else
               { 
                 con = false;
                 document.getElementById("CustomValidator1").innerHTML = "Please Select file!";
               }
             if( _pageStatus == true)
               {
                 var file1 = args.Value.substring(args.Value.length - 3, args.Value.length); //doc
                 if( file1 == "doc")
                 { 
                    _pageStatus = true;
                 }
                 else
                 { 
                    _pageStatus = false;
                    document.getElementById("CustomValidator1").innerHTML = "You can upload doc file only.";
                  }
               }
             if( _pageStatus == true)
               { args.IsValid = true;}
             else
               { args.IsValid = false;}
           }
      

You should also provide server validation code as well to perform both ways. this is to minimize error on server side in case client side validation get failed. [ techincal reasons..] Implement same logic here in server validation function to avoid runtime error.

asp.net page controls .aspx.vb file

Protected Sub CustomValidator1_ServerValidate(ByVal source As Object, ByVal args As System.Web.UI.WebControls.ServerValidateEventArgs) Handles CustomValidator1.ServerValidate
    Dim _pageStatus As Boolean = True
    If args.Value <> ("") Then
       _pageStatus = True
    Else
       _pageStatus = False
       CustomValidator1.Text = "Please select File!"
    End If
    If _pageStatus Then
       Dim file1 As String = args.Value.Substring(args.Value.Length - 3, args.Value.Length)
       If file1.Equals("doc") Then
         _pageStatus = True
       Else
         _pageStatus = False
         CustomValidator1.Text = "You can upload file such as .doc"
       End If
    End If
    If _pageStatus Then
        args.IsValid = True
    Else
        args.IsValid = False
    End If
End Sub

this will solve your problem of file upload with limited extension.