ASP.NET & C# Question: System.NullReferenceException: Object reference not set to an instance of an object.

try ItemInserted instead.  also the value may not be found if your details view is getting wiped out before or information is not loaded on  your page load.

My goal is to do a customized input validation.  I thought OnItemInserting event is a good place to read in the user input and do my validation.  (I want to then query the DB to see if the value already exists.)

Anyway, I moved the codes to the OnItemIInserted and I get this error now:

Compiler Error Message: CS0123: No overload for 'DetailsView1_ItemInserted' matches delegate 'System.Web.UI.WebControls.DetailsViewInsertedEventHandler'

Source Error:
Line 76:     </div>
Line 77:     <div id="divInsert">
Line 78:         <asp:DetailsView ID="DetailsView1" runat="server" AutoGenerateRows="False"
Line 79:             DataKeyNames="BinCategoryID" DataSourceID="SqlDataSource2"
Line 80:             Height="50px" Width="125px" OnItemInserting="DetailsView1_ItemInserting"

Thanks,

Aah, I had a wrong param for the function:
        protected void DetailsView1_ItemInserted(object sender, DetailsViewInsertedEventArgs e)
        {
            Label3.Text = e.Values["tbInsertBinCategory"].ToString();

But I still have the same error even under ItemInserted:

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.

Source Error:
Line 84:         protected void DetailsView1_ItemInserted(object sender, DetailsViewInsertedEventArgs e)
Line 85:         {
Line 86:             Label3.Text = e.Values["tbInsertBinCategory"].ToString();

So I'm simply trying to validate the user input if it doesn't exists in the DB already before I let it to be inserted.  If anyone has source codes, that's all I need. Thanks.

ok try

  TextBox txtBox = DetailsView1.FindControl("tbInsertBinCategory");
   if not isnothing(txtBox ) then
     txtBox.text = ""
  end

I just tested and now it works for me please see code below:

    <asp:DetailsView runat="server" ID="DetailsViewTest"  OnItemInserting="DetailsViewTest_ItemInserting" AutoGenerateRows="false" DataKeyNames="ID" Height="50px" Width="125px"
    DefaultMode="Insert" AutoGenerateInsertButton="true">
    <Fields>
        <asp:TemplateField HeaderText="UserName">
            <InsertItemTemplate>
                <asp:TextBox ID="tbInsertBinCategory" runat="server" Text='<%# Bind("username") %>'></asp:TextBox>
            </InsertItemTemplate>
        </asp:TemplateField>
    </Fields>
    </asp:DetailsView>
 
 
    Public Sub DetailsViewTest_ItemInserting(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.DetailsViewInsertEventArgs) Handles DetailsViewTest.ItemInserting
        Dim oTextBox As TextBox = CType(Me.DetailsViewTest.FindControl("tbInsertBinCategory"), TextBox)
        If Not IsNothing(oTextBox) Then
            oTextBox.Text = "Found"
        End If
    End Sub
 
    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        If Not IsPostBack Then
           LoadDetailsView()
        End If
    End Sub

Select allOpen in new window

Well, for some reason I can't get it working so I got rid of the DetailsView and created input boxes to take user inputs and insert to the DB.  Now that's working and I also added a CustomValidator which is working but when the validator is activated (args.IsValid = false), the form still finishes and inserts a record.

[in the .cs]
        public void InsertBinCategory(string bincategory, string active)
        {
        .....
        }

        protected void Button_Add_Click(object sender, EventArgs e)
        {
            InsertBinCategory(TextBox_BinCategory.Text, "");
        }

        protected void CustomValidator_BinCategory(Object source, ServerValidateEventArgs args)
        {
            string strQuery = "SELECT BinCategoryID from BinCategory " +
                                "WHERE BinCategory = '" + args.Value + "'";
            if (ValueExists(strQuery))
                    args.IsValid = false;
            else
                    args.IsValid = true;
        }

        private bool ValueExists(string strQeury)
        {
        .......
        }

[in the .aspx]
<asp:TextBox ID="TextBox_BinCategory" runat="server"></asp:TextBox>
<asp:CustomValidator id="CustomValidator1" Runat="server" ErrorMessage="already exists"
ControlToValidate="TextBox_BinCategory" OnServerValidate="CustomValidator_BinCategory" />
<asp:Button ID="Button_Add" runat="server" onclick="Button_Add_Click" Text="Add" />

I enter a duplicate value and hit submit.  It display the error msg. "already exists" but it still goes thru InsertBinCategory and ends up inserting a record.