datagrids disapear on postback

[fabianus]

I define my datagrids by vb-code (no AutoGenerateColumns) on the first load of my page (If Not Page.IsPostBack Then...). On the first load everything is fine.

But once the user interacts (for example clicks on a calendar-object) the datagrids disabear! Only the datagrids disapear, not other elements - event text that was written in a textbox is stored and reloaded when the user does a postback... but not the datagrids.

Is this normal?

Thank you very much for your help !

P.S. By the way, I am still looking for someone who could be so kind and help me with this other datagrid-problem :

http://www.vbforums.com/showthread.p...17#post2026217

[mendhak]

What happens when you remove the Postback check?

[fabianus]

Hi mendhak,

what postback check ?
I can not find any postback check in the datagrid properties!

But here is an additional information. As I told in my first post, I did create columns by vb-code (see code beneath).

But, if I create a datagrid and I define the columns in the aspx-page like this it works!

<asp:datagrid id="myDataGrid_lastConsumedProducts" style="Z-INDEX: 123; LEFT: 752px; POSITION: absolute; TOP: 80px" runat="server" Width="168px" AutoGenerateColumns="False" OnItemCommand="viewRow" DataKeyField="product_id">
    <Columns>
         <asp:ButtonColumn DataTextField="fullProductName" CommandName="SelsfdectItem"></asp:ButtonColumn>
    </Columns>
</asp:datagrid>

Now this rejoins a bit my other problem:
http://www.vbforums.com/showthread.p...17#post2026217

Because like in this other problem about datagrids (specifically concerning buttonColumns) the vb-code seems to make problems. I call this code (see beneath) only once at the first upload of the page (not at postbacks), as the data do not change (and if they change I recall the same function again that I use at the first upload).

So probably there is a problem in my vb-code (see beneath). But I really need to be able to define the content of my datagrids by vb-code, so if you could help me to understand the problem I would be more than glad!

Here is the vb-code for defining and filling a datagrid and there are two problems with it : first on postbacks the datagrid disabears and secondly I do not know how to make that the buttonColumn that I create here starts a mySub when it is clicked...

Function fill_myDataGrid_todayConsumptions(ByVal Datehour_start As Date, ByVal Datehour_end As Date)
        Dim field_list(,) As String = _
        {{"id", "id"}, _
        {"consumptionDate", translate("consumption date", , myUser.language_id)}, _
        {"fullProductName", translate("product name", , myUser.language_id)}, _
        {"weight", translate("weight", , myUser.language_id)}, _
        {"unit", translate("unit", , myUser.language_id)}, _
        {"productCondition", translate("product condition", , myUser.language_id)}}
 
        Dim myDataset As DataSet = myConsumptions.get_Dataset_of_Consumptions(field_list)
        myDataGrid_todayConsumptions.AutoGenerateColumns = False
        myDataGrid_todayConsumptions.DataSource = myDataset
        myDataGrid_todayConsumptions.DataKeyField = "id"
 
        Dim myColumn As BoundColumn
        For i As Integer = 0 To field_list.Length / field_list.Rank - 1
            myColumn = New BoundColumn
            myColumn.DataField = field_list(i, 0)
            myColumn.HeaderText = field_list(i, 1)
            If i = 0 Then myColumn.Visible = False
            myDataGrid_todayConsumptions.Columns.Add(myColumn)
        Next
        myDataGrid_todayConsumptions.HeaderStyle.CssClass = "Lable"
        Dim myButtonColumn As ButtonColumn = New ButtonColumn
        myButtonColumn.Text = translate("Edit", , myUser.language_id)
        myButtonColumn.ItemStyle.CssClass = "datagridEditButton"
        myButtonColumn.CommandName = "Delete"
        myDataGrid_todayConsumptions.Columns.Add(myButtonColumn)
        myDataGrid_todayConsumptions.DataBind()
    End Function

[Danial]

Havent read the rest of the reply so not sure if you have solved your problem. But usually if you have the EnableViewState property to false then your DataGrid will dissappear if you are binding it dynamically. So check the EnableViewState property of your datagrid.

[fabianus]

EnableViewState was checked (true). But by changing this the problem does not solve.

Do you have any other idea?

[mendhak]

Postback check = "If Not Page.IsPostBack Then.."

[fabianus]

Hi mendhak,

If I get off the Postback check, the content of the datagrid will be defined at each postback (even if the data do not change), and this would cost time...

I played a bit around to understand what happens, and I think that I have the answer - could you please tell me what you think about it?

Normally the "enableViewState" indicates, if the page-object should keep the control's state in memory from one postback to the next, so that data are not lost – right?

But this seems only to work if the columns of the datagrid are defined in the html-code of the aspx-page … and not if the columns are added by code.

What do you think about it? Could this be?


Here my text-code, in this case too the datagrid disappears once the button is clicked!

Public Class WebForm1
    Inherits System.Web.UI.Page
 
#Region " Web Form Designer Generated Code "
 
    'This call is required by the Web Form Designer.
    <System.Diagnostics.DebuggerStepThrough()> Private Sub InitializeComponent()
 
    End Sub
    Protected WithEvents DataGrid1 As System.Web.UI.WebControls.DataGrid
    Protected WithEvents Button1 As System.Web.UI.WebControls.Button
    Protected WithEvents TextBox1 As System.Web.UI.WebControls.TextBox
 
    'NOTE: The following placeholder declaration is required by the Web Form Designer.
    'Do not delete or move it.
    Private designerPlaceholderDeclaration As System.Object
 
    Private Sub Page_Init(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Init
        'CODEGEN: This method call is required by the Web Form Designer
        'Do not modify it using the code editor.
        InitializeComponent()
    End Sub
 
#End Region
 
    Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        If Not Page.IsPostBack Then
            Dim myDBconnectionManagement As New db_connection_management
            myDBconnectionManagement.SetConnection()
 
            Dim myDataset As DataSet = New DataSet
 
            Dim sql As String = "select * from consumption"
            myDBconnectionManagement.fill_dataset(myDataset, sql, "table")
 
            Dim field_list(,) As String = _
            {{"id", "id"}, _
            {"Date", Translate("consumption date")}, _
            {"Product_id", Translate("product name")}, _
            {"weight", Translate("weight")}, _
            {"unit_id", Translate("unit")}, _
            {"product_condition_id", Translate("product condition")}}
 
            Dim myColumn As BoundColumn
            For i As Integer = 0 To field_list.Length / field_list.Rank - 1
                myColumn = New BoundColumn
                myColumn.DataField = field_list(i, 0)
                myColumn.HeaderText = field_list(i, 1)
                If i = 0 Then myColumn.Visible = False
                DataGrid1.Columns.Add(myColumn)
            Next
            Dim myButtonColumn As ButtonColumn = New ButtonColumn
            myButtonColumn.Text = Translate("Edit")
            myButtonColumn.ItemStyle.CssClass = "datagridEditButton"
            myButtonColumn.CommandName = "Delete"
            DataGrid1.Columns.Add(myButtonColumn)
 
            DataGrid1.AutoGenerateColumns = False
            DataGrid1.DataSource = myDataset
 
            DataGrid1.DataKeyField = "id"
 
            DataGrid1.HeaderStyle.CssClass = "label"
            DataGrid1.ItemStyle.CssClass = "datagrid"
            DataGrid1.DataBind()
        End If
    End Sub
 
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        TextBox1.Text = "now the datagrid will not show-up anymore!"
    End Sub
End Class