Protected Sub Page_Init(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Init
	' Validate Querystrings
	' Set raw querystring values to local variables, by definition,
	' these are strings.
	Dim RawSubjectID As String = Request.QueryString("SubjectID")
	Dim RawGroupID As String = Request.QueryString("GroupID")
	Dim RawTypeID As String = Request.QueryString("TypeID")
	
	' Check for empty string values (querystring value not passed) and
	' validate the expected data type:
	'    Array: IsArray(<obj to validate>)
	'    Date: IsDate(<obj to validate>)
	'    Integer: Int32.TryParse(<value to parse>, <variable to set if successful)
	'    
	If (Not String.IsNullOrEmpty(RawSubjectID) And Int32.TryParse(RawSubjectID, SubjectID)) And _
	    (Not String.IsNullOrEmpty(RawGroupID) And Int32.TryParse(RawGroupID, GroupID)) And _
	    (Not String.IsNullOrEmpty(RawSubjectID) And Int32.TryParse(RawTypeID, TypeID)) Then
	
	    ' Querysting validated, add code here...          
	
	End If
End Sub

Querystring Validation

VB.NET