[sirjohnofthewest]

This function will give you 100% control over the QueryString -- perfect for programmers who use QueryString manipulation a lot.

I wrote this function when I kept having to change values of the QueryString and remove some, add some, etc., etc..

It takes four (4) parameters:

oldUrl = the current QueryString you would like manipulated
qsName = the name of the QueryField you would like to modify/remove/add
newValue = the new value you would like for the QueryField. set to "" if removing
del = an optional integer bit flag; if set to 1 it will remove the QueryField/QueryFieldValue from the QueryString.

Here is the code, enjoy! (I am always welcome to new suggestions)

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1. Function ChangeValue(ByVal oldUrl As String, ByVal qsName As String, ByVal newValue As String, Optional ByVal del As Integer = 0) As String
2.  
3.     Dim newUrl As String = ""
4.  
5.     ' Check if the [qsName] is currently in the [oldUrl]
6.     If InStr(oldUrl, qsName & "=")
7.  
8.         oldUrl += "&"
9.  
10.         Dim pos1 As Integer, pos2 As Integer
11.  
12.         If del = 1
13.             pos1 = oldUrl.IndexOf(qsName & "=")
14.             pos2 = oldUrl.IndexOf("&", pos1) + 1
15.         Else
16.             pos1 = oldUrl.IndexOf(qsName & "=") + qsName.Length + 1
17.             pos2 = oldUrl.IndexOf("&", pos1)
18.         End If
19.  
20.         Dim chunk_1 As String = oldUrl.SubString(0, pos1)
21.         Dim chunk_2 As String = oldUrl.SubString(pos2)
22.  
23.         If del = 1
24.             newUrl = chunk_1 & chunk_2
25.         Else
26.             newUrl = chunk_1 & newValue & chunk_2
27.         End If
28.  
29.         newUrl = newUrl.SubString(0, (newUrl.Length - 1))
30.  
31.     Else
32.  
33.         If del = 1
34.             Return oldUrl
35.         End If
36.  
37.         ' Append the new value to the [oldUrl] and make it a [newUrl]
38.         If oldUrl.EndsWith("?")
39.             newUrl = oldUrl & qsName & "=" & newValue
40.         ElseIf InStr(oldUrl, "?") AndAlso oldUrl.EndsWith("?") = False
41.             If oldUrl.EndsWith("&")
42.                 newUrl = oldUrl & qsName & "=" & newValue
43.             Else
44.                 newUrl = oldUrl & "&" & qsName & "=" & newValue
45.             End If
46.         Else
47.             newUrl = oldUrl & "?" & qsName & "=" & newValue
48.         End If
49.  
50.     End If
51.  
52.     Return newUrl
53.  
54. End Function
55.  

Here is an example:
We have the querystring

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1. http://www.yourdomain.com/search.aspx?fulltext=cat&author=bill+nye&type=scientist&age=45

Now I want to change the "fulltext" to "dog" and the "author" to "bob dole"
Also, I want to remove "type" from the QueryString.

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1. Dim newUrl = Request.RawUrl.ToString()
2. newUrl = ChangeValue(newUrl, "fulltext", "dog")
3. newUrl = ChangeValue(newUrl, "author", "bob dole")
4. newUrl = ChangeValue(newUrl, "type", "", 1)
5.  

The QueryString would now look like this:

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1. http://www.yourdomain.com/search.aspx?fulltext=dog&author=bob+dole&age=45

Yes! It's that easy!