Question

GridView1I am trying to switch my code on gridview from this:

        <asp:SqlDataSource ID="dsPar" runat="server" ConnectionString="<%$ ConnectionStrings:connstring %>"
        SelectCommand="SELECT ID,  FileNumber, address, phone from myTable ORDER BY ID"  FilterExpression="ID like '%{0}%'">
        <FilterParameters>
        <asp:ControlParameter Name="StreetSrch" ControlID="searchBox" PropertyName="Text" />
        </FilterParameters>
        </asp:SqlDataSource>

to this:

    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        Dim strQuery As String = "SELECT ID,  FileNumber, address, Phone from MyTable WHERE Id LIKE '%@strSearch%'  ORDER BY Id"

        Dim cmd As New SqlCommand(strQuery)
        Dim dt As DataTable = GetData(cmd)
        Dim CheckBoxArray As ArrayList
        If ViewState("CheckBoxArray") IsNot Nothing Then
            CheckBoxArray = DirectCast(ViewState("CheckBoxArray"), ArrayList)
        Else
            CheckBoxArray = New ArrayList()
        End If

        If Not IsPostBack Then
            Gridview1.DataBind()
            Dim CheckBoxIndex As Integer
            Dim CheckAllWasChecked As Boolean = False
            Dim chkAll As CheckBox = DirectCast(GridView1.HeaderRow.Cells(0).FindControl("chkAll"), CheckBox)
rest of code....
End If
End Sub

Finally, below is a snapshot of the markup:

<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False" AllowPaging="True"
                OnPageIndexChanging = "OnPaging" HeaderStyle-CssClass = "header" Font-Size = "10pt" 
                 AlternatingRowStyle-BackColor = "#C2D69B" OnRowDataBound = "RowDataBound" AllowSorting="true" 
                 PageSize="20" CssClass="Gridview" 
                 GridLines="None">

I am getting "Object reference not set to an instance of an object." on the following line:

Line 44: Dim chkAll As CheckBox = DirectCast(GridView1.HeaderRow.Cells(0).FindControl(“chkAll”), CheckBox)

Any idea how to resolve this?

Code is very long and I didn’t want to post all of it here. I can post more if needed.

Answer 1

IT is throwing a null reference exception because

GridView1.HeaderRow.Cells(0).FindControl("chkAll")

doesn’t find a checkbox so it returns null (Nothing) so what you are essentially doing is trying to cast Nothing to a checkbox.