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URI.TryCreate examples

Mar 22

Written by: Steve Gray
3/22/2011 5:55 PM

Recently I needed to concatenate two strings and form a URI. I had the base stored in the site config; then we needed to add the page onto that. I wanted to be sure that I didn’t have errors if the user added or didn’t add ‘/’ to the URI in the config so I started with Path.combine. <smiles> That worked (sort of) but it used the wrong ‘/’ and it generated an error.

Enter URI.TriCreate. According to the documentation this would do the trick. But the documentation didn’t have any examples; and I couldn’t figure out the syntax. How bad is the documentation if you read all the way through it and still don’t have a clue?

At any rate, I searched on line for a while and put it all together. Here are code sample for the three overloads.

A few definitions so that you don’t have the same issues that I did:

URI: Uniform Resource Identifier. A string of characters used to identify a name or a resource on the Internet.
UriKind: URIs can be Absolute or Relative. “www.devshed.us” is Absolute. “/links.aspx” is relative.

Code Snippet
 Module Module1
 
    Sub Main()
        TryCreate1()
        TryCreate2()
        TryCreate3()
    End Sub
 
    Sub TryCreate1()
        'demonstrates Uri.TriCreate(Uri,String,Uri)
        Dim UriIn As Uri = New Uri("http://devshed.us/")
        Dim strPage As String = "/links.aspx"
        Dim UriOut As Uri = Nothing
 
        If Uri.TryCreate(UriIn, strPage, UriOut) Then
            Debug.Print(UriOut.ToString)
        Else
            Throw New Exception("Invalid URI")
        End If
    End Sub
    Sub TryCreate2()
        'demonstrates Uri.TriCreate(String,Urikind, Uri)
        'this form doesn't create anything. It just tells us if the URI that we're passing 
        'in the first parameter is Relative or Absolute. Or valid at in any form
 
        'test to see if this string is a valid URI
        Dim strUrl As String = "http://devshed.us/"
 
        'placeholder for our output
        Dim UriOut As Uri = Nothing
 
        'see if our input qualifies as an Absolute URI
        If Uri.TryCreate(strUrl, UriKind.Absolute, UriOut) Then
            'yes
            Debug.Print(UriOut.ToString & " is absolute")
        Else
            'no
            Debug.Print(strUrl & " is not absolute")
        End If
 
        'see if our input qualifies as a Relative URI
        If Uri.TryCreate(strUrl, UriKind.Relative, UriOut) Then
            'yes
            Debug.Print(UriOut.ToString & " is Relative")
        Else
            'no
            Debug.Print(strUrl & " is not Relative")
        End If
 
        'same as above, but this time with a string that is Relative
        strUrl = "/index.aspx"
        If Uri.TryCreate(strUrl, UriKind.Absolute, UriOut) Then
            Debug.Print(UriOut.ToString & " is absolute")
        Else
            Debug.Print(strUrl & " is not absolute")
        End If
 
        If Uri.TryCreate(strUrl, UriKind.Relative, UriOut) Then
            Debug.Print(UriOut.ToString & " is Relative")
        Else
            Debug.Print(strUrl & " is not Relative")
        End If
    End Sub
    Sub TryCreate3()
        'demonstrates Uri.TriCreate(Uri,Uri,Uri)
        'concatonates the first two URIs into the third
 
        'get a base uri
        Dim BaseUri As Uri = New Uri("http://devshed.us/")
 
        'note that we have to specify the urikind
        Dim RelativeUri As New Uri("/links.aspx", UriKind.Relative)
 
        'placeholder for the return val
        Dim UriOut As Uri = Nothing
 
        'add the two together
        If Uri.TryCreate(BaseUri, RelativeUri, UriOut) Then
            Debug.Print(UriOut.ToString)
        Else
            Throw New Exception("Invalid URI")
        End If
 
    End Sub
 
End Module
 

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