Cascading ComboBoxes causes radGrid to reBind

[Tim]

I'm having a logic issue.  I have some Comboboxes that I need to cascade while in Edit or Insert Mode.  The problem is when I Bind the second Combo based on the first, the entire Grid does a PostBack and so the Combos rebind again.

I know i'm likely just missing an 'If Postback' or something, but my brain is mush right now.

 

<telerik:RadGrid ID="RecipientsGrid" runat="server" AutoGenerateColumns="false" EnableViewState="true" PageSize="5" AllowFilteringByColumn="true" AllowPaging="true" AllowSorting="True">

<EditFormSettings EditFormType="Template">

<FormTemplate>

<telerik:RadComboBox ID="CountryCombo" runat="server">

 

</telerik:RadComboBox>

<telerik:RadComboBox ID="ProvinceCombo" runat="server" Width="325" >

</telerik:RadComboBox>

</FormTemplate>

</EditFormSettings>

</telerik:RadGrid>

    Private Sub RecipientsGrid_ItemDataBound(sender As Object, e As Telerik.Web.UI.GridItemEventArgs) Handles RecipientsGrid.ItemDataBound

        If TypeOf e.Item Is GridEditFormItem AndAlso e.Item.IsInEditMode Then
            Dim editItem As GridEditFormItem = DirectCast(e.Item, GridEditFormItem)
            Dim ProvinceCombo As RadComboBox = TryCast(editItem.FindControl("ProvinceCombo"), RadComboBox)
            Dim CountryCombo As RadComboBox = TryCast(editItem.FindControl("CountryCombo"), RadComboBox)
            Dim CityCombo As RadComboBox = TryCast(editItem.FindControl("CityCombo"), RadComboBox)
            '** Populate ComboBoxes and define their Default Value
            Using context As New DataEntities
                With CountryCombo
                    .DataValueField = "CountryId"
                    .DataTextField = "CountryName"
                    .DataSource = context.Countries.OrderBy(Function(x) x.displayOrder).ToList
                End With
                CountryCombo.Width = Unit.Pixel(320)
                CountryCombo.DataBind()
            End Using

            Using context As New DataEntities
                With ProvinceCombo
                    .DataValueField = "ProvinceId"
                    .DataTextField = "NameEnglish"
                    .DataSource = context.Provinces.Where(Function(x) x.CountryId = CountryId).OrderBy(Function(x) x.NameEnglish).ToList

                End With
                ProvinceCombo.Width = Unit.Pixel(320)
                ProvinceCombo.DataBind()
            End Using


            Using context As New DataEntities
                With CityCombo
                    .DataValueField = "CityId"
                    .DataTextField = "CityName"
                    .DataSource = context.Cities.Where(Function(x) x.ProvinceID = ProvinceId).OrderBy(Function(x) x.CityName).ToList
                End With
                CityCombo.Width = Unit.Pixel(320)
                CityCombo.DataBind()
            End Using
            SetComboBoxDefault(CountryId, CountryCombo, "Country")
            SetComboBoxDefault(ProvinceId, ProvinceCombo, "Province/State")
            SetComboBoxDefault(CityId, CityCombo, "City")


        End If


    End Sub

    Public Sub SetComboBoxDefault(ByVal FindItemByValue As Integer, ByVal Control As RadComboBox, ByVal DisplayText As String)

        Dim ComboBoxItem As RadComboBoxItem

        If FindItemByValue >0 Then
            ComboBoxItem = Control.FindItemByValue(FindItemByValue)
            ComboBoxItem.Selected = True

        Else
            Control.Items.Insert(0, New RadComboBoxItem("-- Please select a " & DisplayText & " --", String.Empty))
        End If

    End Sub

    Private Sub RecipientsGrid_ItemCreated(sender As Object, e As Telerik.Web.UI.GridItemEventArgs) Handles RecipientsGrid.ItemCreated
If TypeOf e.Item Is GridEditFormItem AndAlso e.Item.IsInEditMode Then

            'if the item is in edit mode
            Dim editItem As GridEditFormItem = DirectCast(e.Item, GridEditFormItem)
            Dim CountryCombo As RadComboBox = DirectCast(editItem.FindControl("CountryCombo"), RadComboBox)
            CountryCombo.AutoPostBack = True

            AddHandler CountryCombo.SelectedIndexChanged, AddressOf CountryCombo_SelectedIndexChanged

        End If


    End Sub

    Protected Sub CountryCombo_SelectedIndexChanged(ByVal sender As Object, ByVal e As RadComboBoxSelectedIndexChangedEventArgs)

        If RecipientsGrid.MasterTableView.IsItemInserted <> False Then

            Dim insertItem As GridEditFormInsertItem = DirectCast(TryCast(sender, DropDownList).NamingContainer, GridEditFormInsertItem)

            Dim ddlList As DropDownList = DirectCast(insertItem.FindControl("Dropdownlist2"), DropDownList)
        Else

            Dim CountryCombo As RadComboBox = DirectCast(sender, RadComboBox)
            Dim editedItem As GridEditableItem = DirectCast(TryCast(sender, RadComboBox).NamingContainer, GridEditableItem)
            Dim ProvinceCombo As RadComboBox = DirectCast(editedItem.FindControl("ProvinceCombo"), RadComboBox)

            Using context As New DataEntities
                With ProvinceCombo
                    .DataValueField = "ProvinceId"
                    .DataTextField = "NameEnglish"
                    .DataSource = context.Provinces.Where(Function(x) x.CountryId = e.Value).OrderBy(Function(x) x.NameEnglish).ToList
                End With
                ProvinceCombo.Width = Unit.Pixel(320)
                ProvinceCombo.DataBind()
            End Using

        End If

    End Sub

[Tsvetoslav]

Hello Tim,

I could not see anything suspicious in your code - furthermore, you have put the data-binding code for the combos in the ItemDataBound event and that's executed only when the grid rebinds/databinds. I suspect that you are calling the grid's DataBind() method in the Page_Load event or at least are using Simple Databinding as opposed to Advanced data-binding. Do rework your code along the lines of the latter approach and see the result.


Greetings, Tsvetoslav
the Telerik team