Technical Insights: Azure, .NET, Dynamics 365 & EV Charging Architecture

Category: VB.NET

VB.NET

Provide Link to a file without showing the actual path in asp.net

Let’s say you have some file that allow people to download it but you don’t want to expose the actual path for security reason.

Here is the way of doing it, You need to read the file and put that on byte variable then you start omitting slowly instead of the whole chunk. In the next article you will see the error if you omit a big file at once

Public Sub DishUpCFile(ByVal filename As String)

            Dim nBytesRead As Integer = 0
            Const mSize As Integer = 1024
            Dim bytes As Byte() = New Byte(mSize - 1) {}

           'Open or override a file in the local directory
            Dim fsFile As New FileStream(filename, FileMode.Open, FileAccess.Read, FileShare.Read)

            Response.Clear()
            Response.Buffer = True
            Response.ClearHeaders()
            Response.ContentType = "text/csv"
            Response.AddHeader("Content-Disposition", "attachment; filename=AllMembers.csv")

            'Read the first bit of content, then write and read all the content
            'From the FromStream to the ToStream.
            nBytesRead = fsFile.Read(bytes, 0, mSize)

            While nBytesRead > 0
                Response.OutputStream.Write(bytes, 0, nBytesRead)
                nBytesRead = fsFile.Read(bytes, 0, mSize)
            End While

            Response.OutputStream.Close()
            fsFile.Close()
        End Sub

Get Selected Item with Gridview in ASP.NET

I was having a problem before to get selected item with grid view when you click edit button. After spending sometime researching on the internet. I found that we can get the item that you selected by using DataKeynames



      
      
      
      
      
      
      


  Protected Sub gvPlayerSearch_RowCommand(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.GridViewCommandEventArgs) Handles gvPlayerSearch.RowCommand

            If (e.CommandName = "ViewResult") Then
               //casting the object to gridview
                Dim gv As GridView = DirectCast(sender, GridView)

                Dim objEventResults As  MembersDatasetTableAdapters.EventsResultByMemberIDTableAdapter = _
                                        New   MembersDatasetTableAdapters.EventsResultByMemberIDTableAdapter()

   //get the selected ID
   Dim dtEventResults As MembersDataset.EventsResultByMemberIDDataTable = _
                                objEventResults.EventsResultByMemberID(gv.DataKeys(0).Value)

   gvPlayerListEvent.DataSource = dtEventResults
   gvPlayerListEvent.DataBind()
  End If
End Sub

Dynamic array in VB/VB.NET/ASP

Time to go back to old school ASP, I found that i need to create an array that contains a list of languages from a table in database. I would like to make this array length as many as the number of rows in language table. yes you can do it through keyword of ReDim and Preserve

     <%
                dim objLanguage
                dim languageCount
                dim languageArray()

                languageCount = 0

                set objLanguage = Server.CreateObject("ADODB.Recordset")
                objLanguage.ActiveConnection = MM_CTG_STRING
                objLanguage.Source = "SELECT * FROM Languages"
                objLanguage.CursorType = 0
                objLanguage.CursorLocation = 2
                objLanguage.LockType = 3
                objLanguage.Open()

                WHILE NOT objLanguage.EOF
                    response.Write("

") response.Write(objLanguage("Language")) response.Write("

") ReDim Preserve languageArray(languageCount) languageArray(languageCount) = objLanguage("LanguageID") languageCount = languageCount + 1 objLanguage.MoveNext() WEND objLanguage.Close() Set objLanguage = nothing %>

How to clear a gridview

Normally, we would like to clear a gridview for various reason. I want the data to be cleared from grid view everytime user does the search and the grid view will be binded again if the user click a particular button otherwise the last result will be displayed when the new dataset/datatable does not return any rows. This is the simplest way i ever think of

gvPlayerListEvent.DataSourceID = String.Empty
gvPlayerListEvent.DataBind()

Only one instance of script manager can be added to the page

I’ve got this error when i have ajax toolkit script manager on the master page while at the same time i’ve script manager on the content page. This is the primary cause of this error.

The work around this is to move the script manager which is located on the master page before the content place holder or if you have any user control which uses script manager as well, place before it. It should be placed on the top of anything which uses this control and the most important thing you need to change the script manager in the content page or user control to be script manager proxy

407 Proxy authentication required

I found this problem when i try to do any of httpweb request behind proxy and i got error of “407 proxy authentication required”. Normally your company has its own proxy server and sometimes you want to call webservice or reading XML from any website or sending xml to payment gateway.

The workaround this is to use proxy properties of your httpwebrequest variable. this is some snippet

         Dim objRequest As HttpWebRequest
         objSendXML = New XmlDocument
         objRequest = WebRequest.Create(strPaymentURL)
         objRequest.Method = "POST"
         objRequest.ContentLength = strSend.Length
         objRequest.ContentType = "text/xml"

        'for development only!!! have to be blocked on production
         objRequest.Proxy = New System.Net.WebProxy("http://proxy-syd:8080", True)
         objRequest.Proxy.Credentials = CredentialCache.DefaultCredentials

Now you can call your webservice or reading xml behind the proxy server

not valid Base64 character when doing redirect with query string

I was having a problem in my checkout page, the problem that i had was i’ve got this memberID from the checkout page and it’s being passed to another page via query string. This problem doesn’t happen everytime and it happens rarely, this is what i hate the most!!. After spending a couple of hours, i found the problem is in the query string it self.

when you pass something like this in query string

“c+ckDQiiilyW4r7moRA8oQ==”

and it will be automatically converted becoming

“c ckDQiiilyW4r7moRA8oQ==”

and when you try to decrypt it, it will throw the exception of “not valid Base64 character”

“+” when you pass it to url it will be automatically converted to ” “(blank space)

The work around of this problem is

on the target page, you can do some string replace of ” “(blank space) with “+” , and voila it works!!!!

Dim strQuery As String = Request.QueryString("OrderID")
strQuery = strQuery.Replace(" ", "+")

Failed to enable constraints, one or more rows contain values violating non null, unique or foreign-key constraints

I found this error on my project. Well i spent around one hour to figure out this problem. People might think that this is some silly error message.

The error message i got is “Failed to enable constraints, one or more rows contain values violating non null, unique or foreign-key constraints”.

this is caused by my stored procedure which is

SELECT e.eventid,e.event,e.eventdate,i.email,u.username
,u.firstname,u.surname,i.senttime,i.readtime,i.respond
FROM invitefriends i
inner join users u ON i.franchiseeid=u.userid
inner join events e ON i.eventid = e.eventid
WHERE i.franchiseeid is not null
    and ( (@EventID IS NULL) or (e.eventid=@EventID) )
ORDER BY e.eventdate DESC
GO

Since the query is returning multiple rows with the same eventid and the primary key in my datatable is eventid then it caused the error.

There are two workaround to this problem:

  • by using identity from your own table or you can generate it from your query and you need to regenerate your datatable and make sure check the primary key in datatable since it’s not automatically changed for you.
  • You can also relax the constraint by removing the Primary key on the DataTable
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