[RESOLVED] Programatically create (and remove) linkbuttons

[davebat]

Hello,

Here is my scenario. I have an asp.net Image map (needed this for postbacks), that is generated from xml, clicking a hotspot will postback and then either load a different image map or redirect to another page depending on what the postback value of the hotspot is.

Also every time a hotspot is clicked it needs to create a linkbutton to return to it, like a breadcrumb.

Here is my relevant code:

 Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        If Not Page.IsPostBack Then

            Dim ctrlTable As DataTable
            ctrlTable = New DataTable
            Dim ctrlID As DataColumn = New DataColumn("ctrlID")
            Dim ctrlText As DataColumn = New DataColumn("ctrltext")
            Dim ctrlCommand As DataColumn = New DataColumn("ctrlcommand")
            Dim ctrlType As DataColumn = New DataColumn("ctrlType")
            ctrlID.DataType = System.Type.GetType("System.String")
            ctrltext.DataType = System.Type.GetType("System.String")
            ctrlCommand.DataType = System.Type.GetType("System.String")
            ctrlType.DataType = System.Type.GetType("System.String")
            ctrlTable.Columns.Add(ctrlID)
            ctrlTable.Columns.Add(ctrlText)
            ctrlTable.Columns.Add(ctrlCommand)
            ctrlTable.Columns.Add(ctrlType)
            ViewState("ctrlTable") = ctrlTable

         
        Else
            If Not ViewState("ctrlTable") Is Nothing Then
                Dim ctrlTable As DataTable
                ctrlTable = ViewState("ctrlTable")

                Dim x As Integer = 1
                For Each dr As DataRow In ctrlTable.Rows
                    Select Case dr("ctrlType")
                        Case "link"
                            Dim lnkbutton As New LinkButton
                            lnkbutton.ID = dr("ctrlID")
                            lnkbutton.Text = dr("ctrltext")
                            lnkbutton.CommandArgument = dr("ctrlcommand")
                            lnkbutton.ToolTip = "Back"
                            AddHandler lnkbutton.Command, AddressOf mylinkEvent
                            plcBreadcrumb.Controls.Add(lnkbutton)
                            If Not x = ctrlTable.Rows.Count Or ctrlTable.Rows.Count = 1 Then
                                plcBreadcrumb.Controls.Add(New LiteralControl(" > "))
                            End If
                        Case "label"
                            Dim lnkLabel As New Label
                            lnkLabel.ID = dr("ctrlID")
                            lnkLabel.Text = dr("ctrltext")
                            plcBreadcrumb.Controls.Add(lnkLabel)
                    End Select
                    x += 1
                Next
            End If
        End If
    End Sub

'Called when hotpost is clicked

 Protected Sub LoadImageMap(ByVal mapID As String)
        Dim cArgument() As String = mapID.Split(";")

        Dim ctrlTable As DataTable
        ctrlTable = ViewState("ctrlTable")

        '//Adds new linkbutton to collection, but only if isnt there already
        Dim lnkDuplicate As Boolean = False
        For Each dr As DataRow In ctrlTable.Rows
            If dr("ctrlCommand") = mapID Then
                lnkDuplicate = True
            End If
        Next

        If lnkDuplicate = False Then
            '//Item doesnt exist so user has gone forward
            Dim row As DataRow = ctrlTable.NewRow()
            row("ctrlID") = "lbl" & ctrlTable.Rows.Count
            row("ctrlType") = "label"
            row("ctrlText") = cArgument(1)
            row("ctrlCommand") = cArgument(0) & ";" & cArgument(1)
            ctrlTable.Rows.Add(row)

            ViewState("ctrlTable") = ctrlTable
            Dim lnkLabel As New Label
            lnkLabel.ID = "lbl" & ctrlTable.Rows.Count
            lnkLabel.Text = cArgument(1)
            plcBreadcrumb.Controls.Add(lnkLabel)
        End If

        Dim map = New DataSet
        map.ReadXml(MapPath("/xml/" & cArgument(0)))

        If Not map Is Nothing AndAlso map.Tables(0).Rows.Count > 0 Then
            For Each dr As DataRow In map.Tables(0).Rows
                Stage3Map.ImageUrl = "~/images/" & dr("src")
                Stage3Map.CssClass = "map"
                Stage3Map.Width = CInt(dr("width"))
                Stage3Map.Height = CInt(dr("height"))
            Next
        End If

        Stage3Map.HotSpots.Clear()

        If map.Tables(1).Rows.Count > 0 Then
            For Each dr As DataRow In map.Tables(1).Rows
                Select Case dr("shape")
                    Case "rect"
                        Dim hotSpot As New RectangleHotSpot
                        hotSpot.PostBackValue = dr("postback") & ";" & dr("title")
                        hotSpot.HotSpotMode = HotSpotMode.PostBack
                        hotSpot.AlternateText = dr("title")
                        Dim splitRect() As String = dr("coords").Split(",")
                        hotSpot.Top = splitRect(0)
                        hotSpot.Left = splitRect(1)
                        hotSpot.Right = splitRect(2)
                        hotSpot.Bottom = splitRect(3)
                        Stage3Map.HotSpots.Add(hotSpot)
                    Case "circle"
                        Dim hotSpot As New CircleHotSpot
                        hotSpot.PostBackValue = dr("postback") & ";" & dr("title")
                        hotSpot.HotSpotMode = HotSpotMode.PostBack
                        hotSpot.AlternateText = dr("title")
                        Dim splitCircle() As String = dr("coords").Split(",")
                        hotSpot.X = splitCircle(0)
                        hotSpot.Y = splitCircle(1)
                        hotSpot.Radius = splitCircle(2)
                        Stage3Map.HotSpots.Add(hotSpot)
                    Case "poly"
                        Dim hotSpot As New PolygonHotSpot()
                        hotSpot.PostBackValue = dr("postback") & ";" & dr("title")
                        hotSpot.HotSpotMode = HotSpotMode.PostBack
                        hotSpot.AlternateText = dr("title")
                        hotSpot.Coordinates = dr("coords")
                        Stage3Map.HotSpots.Add(hotSpot)
                End Select
            Next
        End If
    End Sub

   Sub mylinkEvent(ByVal sender As Object, ByVal e As CommandEventArgs)

        Dim ctrlTable As DataTable
        ctrlTable = ViewState("ctrlTable")

        Dim lnkDuplicate As Boolean = False
        For Each dr As DataRow In ctrlTable.Rows
            If dr("ctrlCommand") = e.CommandArgument Then
                lnkDuplicate = True
            End If
        Next
        If lnkDuplicate = True Then
            '//Item exists already so user has gone backwards
            ctrlTable.Rows(ctrlTable.Rows.Count - 1).Delete()
        End If

        LoadImageMap(e.CommandArgument)
    End Sub

This is now only creating labels because I changed it to do this for now, what I really need to do is some.

The last sub is when one of the linkbuttons is clicked, it removes this linkbutton from the viewstate collection and then when page reloaded this shouldn't be re-created.

The issue is page load fires before the linkbutton sub, so my controls are re-created before I have had the chance to remove from the collection.

Can anyone offer some advice please?

[brin351]

It's difficult to visualise exactly what the page needs to do but I'll have a go....

Both imagemap and linkbutton postback which runs the breadcrumb code in the page load method. This works when the imagemap causes the postback but conflicts with the lickBtn.command method when it's links button that posts back.

So you need to determine what control caused the postback before running that code. There are a few articles about this here is one

http://ryanfarley.com/blog/archive/2005/03/11/1886.aspx

if you need to convert it to VB try this

http://converter.telerik.com/Default.aspx

[davebat]

Yes Brin thats exactly right, basically clicking a hotspot postback and adds to the breadcrumb (and adds to collection so it can be re-created on next page load).

Clicking the beadcrumb linkbuttons posts back with the previous maps command argument to load it, and should delete all linkbuttons to the right of the clicked one.

Your spot on when you say I need to see which button caused the postback on page load, rather than lettign page load and getting this from linkbuttons command argument.

I'll read the article and let you know. Thansk for the quick reply.

[Pradeep1210]

I have an inking that what you really need is a Repeater control instead of adding each LinkButton/Label inside the loop.

Do you want me to elaborate on this?

[davebat]

Pradeep1210

I think your exactly right, I use repeaters all the time so dont need you to elaborate.

I cant believe I didnt think of this earlier, now you mention it it seems blindingly obvious.

Thanks

[davebat]

Ive done it easily with the repeater thanks, took five minutes and works perfectly

In summary:

Page load processes before any control handlers fire
Think carefully about the best approach to the problem
Im an idiot
Thanks both for your help