Uri

In VB.NET programs, we often need to create and store URIs, or URLs, to remote resources like web servers. This can be done with the Uri and UriBuilder Classes.

To test if a URL is valid, we can use the Uri.TryCreate method. This tester-doer method returns True if the string can be parsed as a URL.

Example

One benefit to storing URLs in Uri objects is that we can access properties on the Uri. These properties can return important parts like the Host or the Scheme (like http).

Module Module1
    Sub Main()
        Dim uri As Uri = new Uri("https://www.dotnetperls.com/")

        ' Print properties of Uri instance.
        Console.WriteLine("AbsolutePath = {0}", uri.AbsolutePath)
        Console.WriteLine("AbsoluteUri = {0}", uri.AbsoluteUri)
        Console.WriteLine("Authority = {0}", uri.Authority)
        Console.WriteLine("DnsSafeHost = {0}", uri.DnsSafeHost)
        Console.WriteLine("Fragment = {0}", uri.Fragment)
        Console.WriteLine("Host = {0}", uri.Host)
        Console.WriteLine("HostNameType = {0}", uri.HostNameType)
        Console.WriteLine("IsAbsoluteUri = {0}", uri.IsAbsoluteUri)
        Console.WriteLine("IsDefaultPort = {0}", uri.IsDefaultPort)
        Console.WriteLine("IsFile = {0}", uri.IsFile)
        Console.WriteLine("IsLoopback = {0}", uri.IsLoopback)
        Console.WriteLine("IsUnc = {0}", uri.IsUnc)
        Console.WriteLine("LocalPath = {0}", uri.LocalPath)
        Console.WriteLine("OriginalString = {0}", uri.OriginalString)
        Console.WriteLine("PathAndQuery = {0}", uri.PathAndQuery)
        Console.WriteLine("Port = {0}", uri.Port)
        Console.WriteLine("Query = {0}", uri.Query)
        Console.WriteLine("Scheme = {0}", uri.Scheme)
        Console.WriteLine("Segments = {0}", String.Join(",", uri.Segments))
        Console.WriteLine("UserEscaped = {0}", uri.UserEscaped)
        Console.WriteLine("UserInfo = {0}", uri.UserInfo)
    End Sub
End Module
AbsolutePath = /
AbsoluteUri = https://www.dotnetperls.com/
Authority = www.dotnetperls.com
DnsSafeHost = www.dotnetperls.com
Fragment =
Host = www.dotnetperls.com
HostNameType = Dns
IsAbsoluteUri = True
IsDefaultPort = True
IsFile = False
IsLoopback = False
IsUnc = False
LocalPath = /
OriginalString = https://www.dotnetperls.com/
PathAndQuery = /
Port = 443
Query =
Scheme = https
Segments = /
UserEscaped = False
UserInfo =

TryCreate

Is a String a valid URL? We can determine this with Uri.TryCreate, and as a bonus we can get the constructed Uri object as a return parameter.

Module Module1
    Sub Main()
        ' Part 1: use Uri.TryCreate on valid url.
        Dim uri1 As Uri = Nothing
        If Uri.TryCreate("http://www.dotnetperls.com/", UriKind.Absolute, uri1)
            Console.WriteLine("1 = {0}", uri1)
        End If

        ' Part 2: handle an invalid Url with Uri.TryCreate.
        Dim uri2 As Uri = Nothing
        If Uri.TryCreate("http:dotnetperls-com", UriKind.Absolute, uri2)
            Console.WriteLine("2 = {0}", uri2) ' Not reached.
        End If
    End Sub
End Module
1 = http://www.dotnetperls.com/

UriBuilder

It is sometimes better to create a Uri object by using the UriBuilder Class. We can set parts like the Host, Path, and Scheme to modify the returned URL.

Module Module1
    Sub Main()
        ' Use UriBuilder constructor.
        Dim u1 As UriBuilder = New UriBuilder("http", "www.dotnetperls.com")
        Console.WriteLine($"UriBuilder: {u1}")

        ' Use UriBuilder properties.
        Dim u2 As UriBuilder = New UriBuilder()
        u2.Host = "www.dotnetperls.com"
        u2.Path = "uribuilder"
        u2.Scheme = "http"
        Console.WriteLine($"UriBuilder: {u2}")

        ' Convert to Uri.
        Dim uri As Uri = u2.Uri
        Console.WriteLine($"       Uri: {uri}")
    End Sub
End Module
UriBuilder: http://www.dotnetperls.com/
UriBuilder: http://www.dotnetperls.com/uribuilder
       Uri: http://www.dotnetperls.com/uribuilder

For complex VB.NET programs, using Uri and UriBuilder to manage URLs is a good idea as it can reduce possible syntax bugs in the resulting URLs. It can lead to more robust programs.