Hi All:
I am trying to create a variation on the standard datagrid, whereby the
datagrid is only shown after pressing some buttons. This reason for
this is that I would like to use the same datagrid for several tables,
and the idea is that the button events store the the SQL select
statement and the SQL update statement in view state items, which can
the be reused for all the datagrid events (paging and editing).
However I seem to have a problem understanding the life cycle of the
page, which is why I would like to ask for some help here.
The error message I keep getting is:
"Object reference not set to an instance of an object.", always
referring to the line:
dgStaffOptions. DataSource = myDataSet.Table s("mytable"
(contained in a sub called showdatagrid() - 'dgStaffOptions ' is the ID
of the datagrid).
Below is the code, which I have simplied for clarity (only the first
button works). The asp:labels and the various reponse.write lines are
elements I have introduced during the bug testing.
HTML side contained in a user control (counter1u.ascx ):
<%@ Control Language="vb" AutoEventWireup ="false"
Codebehind="cou nter1u.ascx.vb" Inherits="qmsne t.counter1u"
TargetSchema="h ttp://schemas.microso ft.com/intellisense/ie5" %>
<h1>Staff Management - Standard options</h1>
<table>
<TBODY>
<tr>
<td vAlign="top">
<TABLE id="Table1" cellSpacing="1" cellPadding="1" width="300"
border="0">
<TR>
<TD><p>Option s</p></TD>
<TD><p>Change </p></TD>
</TR>
<TR>
<TD><p>Position s</p></TD>
<TD align="center"> <asp:button id="Btn_Postion s" Text="Edit"
runat="server"> </asp:button></TD>
</TR>
<TR>
<TD><p>Compan y</p></TD>
<TD align="center"> <asp:button id="Btn_Company " Text="Edit"
runat="server"> </asp:button></TD>
</TR>
</TABLE>
<asp:label id="lbltest" Runat="server"> </asp:label><br>
<asp:label id="lbltest2" Runat="server"> </asp:label>
</td>
<td vAlign="top" width="600">
<asp:datagrid id="dgStaffOpti ons" runat="server" Runat="server"
OnUpdateCommand ="EditDataGrid_ Update"
OnCancelCommand ="EditDataGrid_ Cancel" OnEditCommand=" EditDataGrid_Ed it"
OnPageIndexChan ged="PageChange " AllowPaging="Tr ue" PageSize="4"
autogeneratecol umns="False" Width="400px">
<Columns>
<asp:BoundColum n DataField="ID" ReadOnly="True"
HeaderText="#"> </asp:BoundColumn >
<asp:BoundColum n DataField="Opti ons"
HeaderText="Opt ions"></asp:BoundColumn >
<asp:EditComman dColumn ItemStyle-CssClass="myLis tItem"
ButtonType="Lin kButton" UpdateText="Upd ate" HeaderText="Edi t"
CancelText="Can cel" EditText="Edit" ></asp:EditCommand Column>
</Columns>
</asp:datagrid>
</td>
</tr>
</TBODY>
</table>
Code-behind side (counter1u.ascx .vb):
Imports MySql.Data.MySq lClient
Imports qmsnet.test2
Public Class counter1u
Inherits System.Web.UI.U serControl
#Region " Web Form Designer Generated Code "
'This call is required by the Web Form Designer.
<System.Diagnos tics.DebuggerSt epThrough()> Private Sub
InitializeCompo nent()
End Sub
Protected WithEvents lbltest As System.Web.UI.W ebControls.Labe l
Protected WithEvents Btn_Postions As
System.Web.UI.W ebControls.Butt on
Protected WithEvents Btn_Company As
System.Web.UI.W ebControls.Butt on
Protected WithEvents dgStaffOptions As
System.Web.UI.W ebControls.Data Grid
Protected WithEvents lbltest2 As System.Web.UI.W ebControls.Labe l
'NOTE: The following placeholder declaration is required by the Web
Form Designer.
'Do not delete or move it.
Private designerPlaceho lderDeclaration As System.Object
Private Sub Page_Init(ByVal sender As System.Object, ByVal e As
System.EventArg s) Handles MyBase.Init
'CODEGEN: This method call is required by the Web Form Designer
'Do not modify it using the code editor.
InitializeCompo nent()
End Sub
#End Region
Dim myConnection As MySqlConnection
Dim myDataAdapter As MySqlDataAdapte r
Dim myDataSet As DataSet
Dim strSQLSelect As String
Dim strSQLUpdate As String
Private Sub Page_Load(ByVal sender As System.Object, ByVal e As
System.EventArg s) Handles MyBase.Load
myConnection = New MySqlConnection ("server=mysql. mydomain.com;
user id=root; password=passwo rd; database=mybase ; pooling=false;" )
If Not Page.IsPostBack Then
strSQLSelect = "Select ID, Options from qmsPositions order
by Options"
strSQLUpdate = "Update"
Else
strSQLSelect = ViewState("StrS QLSelect")
strSQLUpdate = ViewState("StrS QLUpdate")
End If
'Response.Write ("load:" & strSQLSelect)
LoadDataFromDB( )
End Sub
Private Sub Page_Prerender( ByVal sender As System.Object, ByVal e
As System.EventArg s) Handles MyBase.PreRende r
Viewstate("strS QLSelect") = strSQLSelect
ViewState("strS QLUpdate") = strSQLUpdate
lbltest.Text = strSQLSelect
lbltest2.Text = strSQLUpdate
End Sub
Sub LoadDataFromDB( )
Order by Options"
myDataAdapter = New MySqlDataAdapte r(strSQLSelect,
myConnection)
myDataSet = New DataSet
Response.Write( "load3:" & strSQLSelect)
myDataAdapter.F ill(myDataSet, "mytable")
End Sub
Private Sub Btn_Postions_Cl ick(ByVal sender As System.Object, ByVal
e As System.EventArg s) Handles Btn_Postions.Cl ick
strSQLSelect = "Select ID, Options from qmsPositions Order by
Options"
strSQLUpdate = "Update qmsPositions set Options = 'columnvalue'
where ID = idvalue"
Showdatagrid()
End Sub
Private Sub Btn_Company_Cli ck(ByVal sender As System.Object, ByVal
e As System.EventArg s) Handles Btn_Company.Cli ck
End Sub
Sub PageChange(ByVa l sender As Object, ByVal e As
DataGridPageCha ngedEventArgs)
dgStaffOptions. CurrentPageInde x = e.NewPageIndex
Showdatagrid()
End Sub
Sub Showdatagrid()
dgStaffOptions. DataSource = myDataSet.Table s("mytable")
dgStaffOptions. DataBind()
End Sub
Sub EditDataGrid_Ed it(ByVal Sender As Object, ByVal E As
DataGridCommand EventArgs)
dgStaffOptions. EditItemIndex = E.Item.ItemInde x
Showdatagrid()
End Sub
Sub EditDataGrid_Ca ncel(ByVal Sender As Object, ByVal E As
DataGridCommand EventArgs)
dgStaffOptions. EditItemIndex = -1
Showdatagrid()
End Sub
Sub EditDataGrid_Up date(ByVal Sender As Object, ByVal E As
DataGridCommand EventArgs)
Dim IDint As String = E.Item.Cells(0) .Text
Dim Options As TextBox = E.Item.Cells(1) .Controls(0)
Dim SQLtemp As String
Dim objCommand As MySqlCommand
SQLtemp = Replace(strSQLU pdate, "columnvalu e", Options.Text)
SQLtemp = Replace(SQLtemp , "idvalue", IDint)
objCommand = New MySqlCommand(SQ Ltemp, myConnection)
Try
myConnection.Op en()
objCommand.Exec uteNonQuery()
myConnection.Cl ose()
Catch Ex As Exception
Response.Write( "<p><strong >An Error Occurred:</strong> " &
Ex.ToString() & "</p>" & vbCrLf)
Finally
myConnection.Cl ose()
End Try
LoadDataFromDB( )
dgStaffOptions. EditItemIndex = -1
Showdatagrid()
End Sub
End Class
=====
Thanks a bundle in advance!!
TB
