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

[mazlina]

i've got this error while running my program. i have dropdownlist in my datagrid for updating my data in dbase.

this is part of my code that i'm using right now.......

 

Dim name As String = e.Item.Cells(1).Text

Dim accessDate As String = e.Item.Cells(0).Text

 

'refrence textbox

Dim approve As String

Dim dataGridItem As DataGridItem

 

approve = CType(e.Item.FindControl("Label1"), DropDownList).SelectedItem.Text

 

updateApprove(accessDate, name, approve)

 

dgApproveStaff.EditItemIndex = -1

dgApproveStaff.DataSource = getStaff()

dgApproveStaff.DataBind()

[Volte]

What line?

[mazlina]

Dim name As String = e.Item.Cells(1).Text

Dim accessDate As String = e.Item.Cells(0).Text

 

'refrence textbox

Dim approve As String

Dim dataGridItem As DataGridItem

 

'error occured at this point

approve = CType(e.Item.FindControl("Label1"), DropDownList).SelectedItem.Text

 

 

updateApprove(accessDate, name, approve)

 

dgApproveStaff.EditItemIndex = -1

dgApproveStaff.DataSource = getStaff()

dgApproveStaff.DataBind()

[Volte]

Is it possible that SelectedItem is nothing, because no item is selected?

 

 

 

Also, why do you have a DropDownList control called "Label1"? :p

[mazlina]

value in SelectedItem is given after user select from the DropDownList right?

 

Label1 is my id.......

 

<asp:TemplateColumn HeaderText="Approval">

<ItemTemplate>

<asp:Label Width="200" Runat="server" text='<%# DataBinder.Eval(Container.DataItem, "Approval") %>' ID="Label1">

</asp:Label>

</ItemTemplate>

<EditItemTemplate>

<asp:ListBox SelectionMode=Single ID="Approval" Runat="server" Rows="1" DataSource="<%# GetApproval()%>" DataTextField="Approval" DataValueField="Approval">

</asp:ListBox>

</EditItemTemplate>

</asp:TemplateColumn>

[mazlina]

is it my syntax error that is not possible for FindControl method?

[wyrd]

Can you give us the exact line the error is on? Step through your code with the debugger if you have to. It could be a number of things.. including the cryptic getStuff() method.

[mazlina]

this is where the error stated :-

 

Source Error:

 

 

Line 131: 'approve = e.Item.Cells(6).Controls(0)

Line 132: 'approve = e.Item.FindControl("Label1")

Line 133: approve = CType(e.Item.Cells(6).Controls(0), ListBox).SelectedItem.Value

Line 134:

Line 135: 'approve = CType(e.Item.FindControl("Label1"), Label).Text

 

 

Source File: c:\inetpub\wwwroot\TimeManagement\WebForm5.aspx.vb Line: 133

 

Stack Trace:

 

 

[invalidCastException: Specified cast is not valid.]

TimeManagement.WebForm5.dgUserAttendance_Update(Object sender, DataGridCommandEventArgs e) in c:\inetpub\wwwroot\TimeManagement\WebForm5.aspx.vb:133

System.Web.UI.WebControls.DataGrid.OnUpdateCommand(DataGridCommandEventArgs e)

System.Web.UI.WebControls.DataGrid.OnBubbleEvent(Object source, EventArgs e)

System.Web.UI.Control.RaiseBubbleEvent(Object source, EventArgs args)

System.Web.UI.WebControls.DataGridItem.OnBubbleEvent(Object source, EventArgs e)

System.Web.UI.Control.RaiseBubbleEvent(Object source, EventArgs args)

System.Web.UI.WebControls.LinkButton.OnCommand(CommandEventArgs e)

System.Web.UI.WebControls.LinkButton.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent(String eventArgument)

System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument)

System.Web.UI.Page.RaisePostBackEvent(NameValueCollection postData)

System.Web.UI.Page.ProcessRequestMain()

 

'------------------------------------------

n this is my exact code

 

Sub dgUserAttendance_Update(ByVal sender As Object, ByVal e As DataGridCommandEventArgs)

 

'determine the value of the StaffID column

 

Dim name As String = e.Item.Cells(1).Text

Dim accessDate As String = e.Item.Cells(0).Text

 

'refrence textbox

Dim approve As String

'Dim dataGridItem As DataGridItem

 

'approve = e.Item.Cells(6).Controls(0)

'approve = e.Item.FindControl("Label1")

 

\***************************************

the error is in this line................

 

approve = CType(e.Item.Cells(6).Controls(0), ListBox).SelectedItem.Value

\***********************************

'approve = CType(e.Item.FindControl("Label1"), Label).Text

'CType(e.Item.FindControl("Label2"), Label).Text

 

updateApprove(accessDate, name, approve)

 

dgApproveStaff.EditItemIndex = -1

dgApproveStaff.DataSource = getStaff()

dgApproveStaff.DataBind()

 

End Sub

 

Function GetApproval()

 

conn = New OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0; Data Source=E:\database\AttendanceReport.mdb;")

myCommandApproval = New OleDbCommand("SELECT * from TableApproval", conn)

 

conn.Open()

 

Dim approvalReader As OleDbDataReader

 

approvalReader = myCommandApproval.ExecuteReader

 

Return approvalReader

approvalReader.Close()

conn.Close()

 

End Function

 

Public Sub ItemDataBound(ByVal sender As Object, ByVal e As DataGridItemEventArgs)

 

If (e.Item.ItemType = ListItemType.EditItem) Then

Dim drv As DataRowView

 

drv = e.Item.DataItem

Dim oldApproval As String

oldApproval = drv("Approval").ToString()

Dim ddl As ListBox = e.Item.FindControl("Approval")

ddl.SelectedIndex = ddl.Items.IndexOf(ddl.Items.FindByText(oldApproval))

 

End If

End Sub

[aewarnick]

The SelectedItem must be null. Check it before you assign the Value member to approve.

if(the SelectedItem is != null) Assign!!