listview, datapager, objectdatasource not working in updatepanel

Question

When i change the page in datapager it causes full postback, even the datapager is working very abnormally, idont know what is the reason. by abnormaaly i mean sometime data is shown sometime doesnt,
Following is th my code in c#

     protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            BindListView();
        }           
    }

    protected void StudentListView_PagePropertiesChanging(object sender, PagePropertiesChangingEventArgs e)
    {
        BindListView();
    }
    private void BindListView()
    {
        StudentListView.DataSource = StudentDataSource;
        StudentListView.DataBind();
    }

    protected void StudentDataSource_Selecting(object sender, ObjectDataSourceSelectingEventArgs e)
    {
        e.Arguments.MaximumRows = StudentListDataPager.MaximumRows;
        e.Arguments.StartRowIndex = StudentListDataPager.StartRowIndex;
    }

Following is my markup

    <asp:UpdatePanel runat="server" UpdateMode="Conditional">
    <ContentTemplate>        <
    <asp:DropDownList runat="server" ID="BatchDropDownList" AutoPostBack="True">
        <asp:ListItem Text="Batch 1" Value="1" Selected="True" />
        <asp:ListItem Text="Batch 2" Value="2" />
    </asp:DropDownList>

    <asp:ListView ID="StudentListView" runat="server"       
        ItemPlaceholderID="ListViewContent" 
            EnableViewState="false" 
            onpagepropertieschanging="StudentListView_PagePropertiesChanging"> 
        <LayoutTemplate> 
            <table style="width:100%">
                <thead>
                    <tr>
                        <th class="align-left"><strong>Name</strong></th>
                        <th class="align-left"><strong>MobNo</strong></th>
                    </tr>
                </thead>
                <tbody runat="server" id="ListViewContent"> 
                </tbody>
                <tfoot>
                    <tr>
                        <td colspan="3">

                        </td>
                    </tr>
                </tfoot>
            </table>

        </LayoutTemplate>  
        <ItemTemplate>  

            <tr>
                <td style="width:70%;"><%# Eval("FirstName") %>&nbsp<%# Eval("LastName") %></td>
                <td style="width:30%;"><%# Eval("MobNo") %></td>                    
            </tr>

        </ItemTemplate>             
    </asp:ListView>
    <asp:DataPager ID="StudentListDataPager" runat="server" PageSize="5" PagedControlID="StudentListView">
        <Fields>
            <asp:NumericPagerField />
        </Fields>
    </asp:DataPager>


    <asp:ObjectDataSource ID="StudentDataSource" runat="server" 
        SelectMethod="GetStudentListBatchWise" SelectCountMethod="StudentCount" 
            TypeName="SCERPCommonUtil.Student" EnablePaging="True" 
            onselecting="StudentDataSource_Selecting">
        <SelectParameters>
            <asp:ControlParameter Name="batchId" ControlID="BatchDropDownList" PropertyName="SelectedValue" />
        </SelectParameters>
    </asp:ObjectDataSource>
    </ContentTemplate>
</asp:UpdatePanel>

Please tell me if i am making any mistakes.

P.S. : Please dont point me to any stackoverflow question as i have read all of them, and none is specific to my requirement,

Most important problem i am facing is that datapager is giving full postback, even if put datapager inside updatepanel same thing happens.

Answer 1

I figured it - incase somebody come looking -

i was using <form runat="server">...<form> tag, inside which all this listview,datapager code was present. When i assigned unique id attribute to form tag then everything started working correctly.
Although i dont understand the reason of such behavior.