If you want to do a check if a url is valid the not so good way to do this is use the Uri class
Uri myUrl = new Url(someString);
This will break if the url is invalid. The Constructor of the Uri class is
if (uriString == null)
throw new ArgumentNullException("uriString");
else
this.CreateThis(uriString, false, UriKind.Absolute);
The CreateThis throws an exception if the uri is invalid.
If you like me and don't like the try catch way of working you can use
Uri myUrl = null;
if (Uri.TryCreate(someString, UriKind.Absolute, out myUrl))
{
}
else
{
}