Object reference not set to an instance of an object.

Question

4.00/5 (1 vote)

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First i want to add data in gridview viewstate and then i've button save into database, but i've problem when i'click save button. please help me, thanks

i have error nmplu was nothing in btnEditSimpanSelected_Click

Quote:
sc.Add(String.Format("{0},{1}", nmplu.Text, desc.Text))

What I have tried:

ASP.NET

<asp:GridView ID="gvPluPlano" runat="server" AutoGenerateColumns="False" AllowPaging="True" OnPageIndexChanging="gvPluPlano_PageIndexChanging" EmptyDataText="No records has been added." PageSize="500" ShowHeaderWhenEmpty="True" AllowSorting="True" headerstyle-cssclass="FixedHeader" Width="850px" style="margin-top: 0px">
                        <HeaderStyle BackColor="Black" ForeColor="White" />
                        <RowStyle BackColor="White" ForeColor="Black" Wrap="false" />
                        <AlternatingRowStyle BackColor="#e5e5e5" ForeColor="Black" />
                        <SelectedRowStyle BackColor="#999999" ForeColor="#fff" />
                        <Columns>
                            <asp:BoundField DataField="NAMAPLU" HeaderText="PLU" ItemStyle-Width="120" />
                            <asp:BoundField DataField="DESKRIPSIPLU" HeaderText="Description" ItemStyle-Width="120" />
                            <asp:TemplateField HeaderText="Action" HeaderStyle-CssClass="header-center">
                                <ItemTemplate>
                                    <asp:LinkButton ID="lbDeletegvPluPlano" runat="server" OnClientClick="return confirm('Are you sure you want to delete?'); " OnClick="lbDeletegvPluPlano_Click" CausesValidation="False" CommandName="Delete" Text="Delete"></asp:LinkButton>
                                </ItemTemplate>
                                <ItemStyle Width="50px" HorizontalAlign="Center" />
                            </asp:TemplateField>
                        </Columns>
                    </asp:GridView>

VB

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

        If Not Me.IsPostBack Then
            If Not Me.IsPostBack Then
                Dim dt As New DataTable()
                dt.Columns.Add(New DataColumn("NAMAMODIS", GetType(String)))
                dt.Columns.Add(New DataColumn("NAMAPLU", GetType(String)))
                dt.Columns.Add(New DataColumn("DESKRIPSIPLU", GetType(String)))
                dt.Columns.Add(New DataColumn("KODETOKO", GetType(String)))
                dt.Columns.Add(New DataColumn("NAMATOKO", GetType(String)))
                dt.Columns.Add(New DataColumn("CABANG", GetType(String)))
                ViewState("dt") = dt
                Me.BindGrid()
            End If
        End If

        If Not Me.IsPostBack Then
            Me.LoadData()
            Me.LoadData2()
            btnBatalSelected.Visible = False
            btnEditSimpanSelected.Visible = False
            btnCopyBaruSelected.Visible = False
        End If
    End Sub

VB

Protected Sub BindGrid()
        gvPluPlano.DataSource = DirectCast(ViewState("dt"), DataTable)
        gvPluPlano.DataBind()
    End Sub

VB

Protected Sub btnEditSimpanSelected_Click(sender As Object, e As EventArgs)
        Dim rowIndex As Integer = 0
        Dim sc As StringCollection = New StringCollection()

        If ViewState("dt") IsNot Nothing Then
            Dim dtCurrentTable As DataTable = CType(ViewState("dt"), DataTable)

            If dtCurrentTable.Rows.Count > 0 Then

                For i As Integer = 1 To dtCurrentTable.Rows.Count
                    Dim nmplu As TextBox = CType(gvPluPlano.Rows(rowIndex).Cells(0).FindControl("txtPlu2"), TextBox)
                    Dim desc As TextBox = CType(gvPluPlano.Rows(rowIndex).Cells(1).FindControl("DESKRIPSIPLU"), TextBox)
                    sc.Add(String.Format("{0},{1}", nmplu.Text, desc.Text))
                    rowIndex += 1
                Next

                InsertRecords(sc)
            End If
        End If

    End Sub

VB

Private Sub InsertRecords(ByVal sc As StringCollection)
        Dim sqlCon As New MySqlConnection(ObjFungsi.ConDataProduction)
        Dim sb As StringBuilder = New StringBuilder(String.Empty)
        Dim splitItems As String() = Nothing
        Const sqlStatement As String = "INSERT INTO master_planogram values (NAMAMODIS,NAMAPLU,DESKRIPSIPLU) VALUES"

        Try
            For Each item As String In sc

                If item.Contains(",") Then
                    splitItems = item.Split(",".ToCharArray())
                    sb.AppendFormat("{0}('{1}','{2}'); ", sqlStatement, splitItems(0), splitItems(1))
                End If
            Next

            sqlCon.Open()

            Using cmd As MySqlCommand = New MySqlCommand(sb.ToString(), sqlCon)
                cmd.CommandType = CommandType.Text
                cmd.ExecuteNonQuery()
            End Using
        Catch ex As Exception
            ObjFungsi.tracelog("error at MasterPlanogram.aspx " + vbCrLf + ex.Message + vbCrLf + ex.StackTrace)
            ObjFungsi.ShowMsgBox("Simpan data SUKSES ! " & ex.Message)
        Finally

            If sqlCon.State = ConnectionState.Open Then
                sqlCon.Close()
            End If
        End Try

    End Sub

Posted 25-Jul-20 22:08pm

SDK Channel

Updated 25-Jul-20 22:13pm

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OriginalGriff · Accepted Answer · 2020-07-25T22:13:00

This is one of the most common problems we get asked, and it's also the one we are least equipped to answer, but you are most equipped to answer yourself.

Let me just explain what the error means: You have tried to use a variable, property, or a method return value but it contains null - which means that there is no instance of a class in the variable.
It's a bit like a pocket: you have a pocket in your shirt, which you use to hold a pen. If you reach into the pocket and find there isn't a pen there, you can't sign your name on a piece of paper - and you will get very funny looks if you try! The empty pocket is giving you a null value (no pen here!) so you can't do anything that you would normally do once you retrieved your pen. Why is it empty? That's the question - it may be that you forgot to pick up your pen when you left the house this morning, or possibly you left the pen in the pocket of yesterdays shirt when you took it off last night.

We can't tell, because we weren't there, and even more importantly, we can't even see your shirt, much less what is in the pocket!

Back to computers, and you have done the same thing, somehow - and we can't see your code, much less run it and find out what contains null when it shouldn't.
But you can - and Visual Studio will help you here. Run your program in the debugger and when it fails, VS will show you the line it found the problem on. You can then start looking at the various parts of it to see what value is null and start looking back through your code to find out why. So put a breakpoint at the beginning of the method containing the error line, and run your program from the start again. This time, VS will stop before the error, and let you examine what is going on by stepping through the code looking at your values.

But we can't do that - we don't have your code, we don't know how to use it if we did have it, we don't have your data. So try it - and see how much information you can find out!

Oh and BTW: don't do SQL like that! Never concatenate strings to build a SQL command. It leaves you wide open to accidental or deliberate SQL Injection attack which can destroy your entire database. Always use Parameterized queries instead.

When you concatenate strings, you cause problems because SQL receives commands like:

SQL

SELECT * FROM MyTable WHERE StreetAddress = 'Baker's Wood'

The quote the user added terminates the string as far as SQL is concerned and you get problems. But it could be worse. If I come along and type this instead: "x';DROP TABLE MyTable;--" Then SQL receives a very different command:

SQL

SELECT * FROM MyTable WHERE StreetAddress = 'x';DROP TABLE MyTable;--'

Which SQL sees as three separate commands:

SQL

SELECT * FROM MyTable WHERE StreetAddress = 'x';

A perfectly valid SELECT

SQL

DROP TABLE MyTable;

A perfectly valid "delete the table" command

SQL

--'

And everything else is a comment.
So it does: selects any matching rows, deletes the table from the DB, and ignores anything else.

So ALWAYS use parameterized queries! Or be prepared to restore your DB from backup frequently. You do take backups regularly, don't you?
And frankly, SQL injection prone code in a website? That's just begging for trouble ...