WORKING WITH DATA in VB.NET

Generation QR-Code in VB.NET WORKING WITH DATA

First create a classic ASP.NET web service (ASMX) named ValidationService that will do validation for a few properties of the Consultant class that we will develop next. As described in 5, we need to add this web service to the chapter6.Web ASP.NET web project. We need to add the following namespaces to develop validation logic. using System.Net; using System.Net.Sockets; using System.Text.RegularExpressions; The web service will expose two methods, named ValidateUrl and ValidateEmail. The ValidateUrl method accepts one string parameter and it validates whether the string supplied is a valid link to web resource. Here is the code for the ValidateUrl method. [WebMethod] public bool ValidateUrl(string URL) { bool isValid = false; try { Dns.GetHostEntry (URL); isValid = true; } catch ( SocketException se) { isValid = false; } return isValid; } As shown in the code snippet, the Dns class with the method GetHostEntry that provides simple domain-name resolution functionality is used to determine the validity of the supplied string URL. If the resource supplied in the URL does not exist or is incorrect, it will raise an exception of the type SocketException. We have a catch block to catch this exception and, according to the validity of the string URL, we set the value for the Boolean flag to isValid and return it. Here is the code for the ValidateEmail method. [WebMethod] public string ValidateEmail(string Email) { string strRegex = @"^([a-zA-Z0-9_\-\.]+)@((\[[0-9]{1,3}" + @"\.[0-9]{1,3}\.[0-9]{1,3}\.)|(([a-zA-Z0-9\-]+\" + @".)+))([a-zA-Z]{2,4}|[0-9]{1,3})(\] )$"; Regex re = new Regex(strRegex); if (re.IsMatch(Email) == false) { return ("E501"); }

else if (Email.Substring(Email.IndexOf("@") + 1 ) == "example.com") { return ("E502"); } return null; } As shown, this method uses a regular expression to validate the format of the supplied string as an email. If it is not a valid email, it returns string value E501, which is an error code for our custom error object that we will develop next. And just for an idea, there is another validation rule to put a ban on email for the domain example.com. If the supplied string email has the example.com domain, the string value E502 as an error code will be returned to the calling environment. At this point, you may be wondering why we used web service to implement this simple validation for email! This validation can also be possible on the client side using the IDataErrorInfo interface. The only reason is to demonstrate asynchronous validation over web service and the use of a custom error object with this interface. In a real usage scenario, you would be using an SMTP network connection and SMTP handshakes to check validity for an email. We avoid such implementation to keep things focused more on the interface itself. This is all required code for the ValidationService web service. To consume this web service, you need to add a service reference of it named ValidationServiceReference in your chapter6 Silverlight application project.

Now create a new class named Consultant that will implement the INotifyDataErrorInfo interface. Make sure that you add this class to the previously created folder INotifyDataErrorInfoDemo in the chapter6 Silverlight project, to keep the same structure as described here. We need to add the following namespaces: using System.ComponentModel; using System.Collections.Generic; using System.Linq; For the ease of understanding, we will divide the code into regions (#region). So let us start with the region private members (#region private members). As you can see in the code snippet, there is a ValidationService soap client proxy vds created and some private string objects to use with public properties that we will develop next. #region private members private ValidationServiceReference.ValidationServiceSoapClient vds = new ValidationServiceReference.ValidationServiceSoapClient(); private string name; private string email; private string websiteurl; #endregion Our custom error class is called ErrorInfo, with public properties and an override version of the ToString method, as shown here. Here we override the default ToString() method to a more meaningful method that outputs ErrorMessage with ErrorCode.