System.NullReferenceException

How must i declare my variables to have this code work. I get
system.nullreferenceexception every time i click button to add data to
datatable
here below is my code :

Dim wykszt as System.Data.DataTable
Dim zatru as System.Data.DataTable

Private Sub Page_Load(s As Object, e As EventArgs)

if Not IsPostBack Then
make_d_tables()
End if
End Sub

sub make_d_tables()

wykszt = New System.Data.DataTable("wykszt")
wykszt.Columns.Add("od_data", GetType(date))
wykszt.Columns.Add("do_data", GetType(date))
wykszt.Columns.Add("nazwa_szkoly", GetType(String))
wykszt.Columns.Add("nazwa_tytulu", GetType(String))

zatru = New System.Data.DataTable("zatr")
zatru.Columns.Add("od_data", GetType(date))
zatru.Columns.Add("do_data", GetType(date))
zatru.Columns.Add("nazwa_prac", GetType(String))
zatru.Columns.Add("nazwa_stan", GetType(String))

End sub

Sub Button2_Click(sender As Object, e As EventArgs)

row = wykszt.NewRow
row("od_data")=TextBox27.Text + "-01"
row("do_data")=TextBox28.Text + "-01"
row("nazwa_szkoly")=TextBox29.Text
row("nazwa_tytulu")=TextBox30.Text
wykszt.Rows.Add(row)
row = wykszt.NewRow
Mxdatagrid1.datasource=wykszt
Mxdatagrid1.databind

End Sub

Thanks

PatYou have to recreate your tables every time. So take out the if statement
from page_load.

"ven" <venome_@.poczta.onet.pl> wrote in message
news:cif6p8$sf3$1@.news.onet.pl...
> How must i declare my variables to have this code work. I get
> system.nullreferenceexception every time i click button to add data to
> datatable
> here below is my code :
> Dim wykszt as System.Data.DataTable
> Dim zatru as System.Data.DataTable
> Private Sub Page_Load(s As Object, e As EventArgs)
> if Not IsPostBack Then
> make_d_tables()
> End if
> End Sub
> sub make_d_tables()
> wykszt = New System.Data.DataTable("wykszt")
> wykszt.Columns.Add("od_data", GetType(date))
> wykszt.Columns.Add("do_data", GetType(date))
> wykszt.Columns.Add("nazwa_szkoly", GetType(String))
> wykszt.Columns.Add("nazwa_tytulu", GetType(String))
> zatru = New System.Data.DataTable("zatr")
> zatru.Columns.Add("od_data", GetType(date))
> zatru.Columns.Add("do_data", GetType(date))
> zatru.Columns.Add("nazwa_prac", GetType(String))
> zatru.Columns.Add("nazwa_stan", GetType(String))
> End sub
> Sub Button2_Click(sender As Object, e As EventArgs)
> row = wykszt.NewRow
> row("od_data")=TextBox27.Text + "-01"
> row("do_data")=TextBox28.Text + "-01"
> row("nazwa_szkoly")=TextBox29.Text
> row("nazwa_tytulu")=TextBox30.Text
> wykszt.Rows.Add(row)
> row = wykszt.NewRow
> Mxdatagrid1.datasource=wykszt
> Mxdatagrid1.databind
> End Sub
>
> Thanks
> Pat
Which line is throwing the exception?
Does the error only happen on postback?

--
I hope this helps,
Steve C. Orr, MCSD, MVP
http://Steve.Orr.net

"ven" <venome_@.poczta.onet.pl> wrote in message
news:cif6p8$sf3$1@.news.onet.pl...
> How must i declare my variables to have this code work. I get
> system.nullreferenceexception every time i click button to add data to
> datatable
> here below is my code :
> Dim wykszt as System.Data.DataTable
> Dim zatru as System.Data.DataTable
> Private Sub Page_Load(s As Object, e As EventArgs)
> if Not IsPostBack Then
> make_d_tables()
> End if
> End Sub
> sub make_d_tables()
> wykszt = New System.Data.DataTable("wykszt")
> wykszt.Columns.Add("od_data", GetType(date))
> wykszt.Columns.Add("do_data", GetType(date))
> wykszt.Columns.Add("nazwa_szkoly", GetType(String))
> wykszt.Columns.Add("nazwa_tytulu", GetType(String))
> zatru = New System.Data.DataTable("zatr")
> zatru.Columns.Add("od_data", GetType(date))
> zatru.Columns.Add("do_data", GetType(date))
> zatru.Columns.Add("nazwa_prac", GetType(String))
> zatru.Columns.Add("nazwa_stan", GetType(String))
> End sub
> Sub Button2_Click(sender As Object, e As EventArgs)
> row = wykszt.NewRow
> row("od_data")=TextBox27.Text + "-01"
> row("do_data")=TextBox28.Text + "-01"
> row("nazwa_szkoly")=TextBox29.Text
> row("nazwa_tytulu")=TextBox30.Text
> wykszt.Rows.Add(row)
> row = wykszt.NewRow
> Mxdatagrid1.datasource=wykszt
> Mxdatagrid1.databind
> End Sub
>
> Thanks
> Pat
Uytkownik "Steve C. Orr [MVP, MCSD]" <Steve@.Orr.net> napisa w wiadomoci
news:OkGuVzNnEHA.1304@.TK2MSFTNGP09.phx.gbl...
> Which line is throwing the exception?
> Does the error only happen on postback?
> --
> I hope this helps,
> Steve C. Orr, MCSD, MVP
> http://Steve.Orr.net
>
> "ven" <venome_@.poczta.onet.pl> wrote in message
> news:cif6p8$sf3$1@.news.onet.pl...
> > How must i declare my variables to have this code work. I get
> > system.nullreferenceexception every time i click button to add data to
> > datatable
> > here below is my code :
> > Dim wykszt as System.Data.DataTable
> > Dim zatru as System.Data.DataTable
> > Private Sub Page_Load(s As Object, e As EventArgs)
> > if Not IsPostBack Then
> > make_d_tables()
> > End if
> > End Sub
> > sub make_d_tables()
> > wykszt = New System.Data.DataTable("wykszt")
> > wykszt.Columns.Add("od_data", GetType(date))
> > wykszt.Columns.Add("do_data", GetType(date))
> > wykszt.Columns.Add("nazwa_szkoly", GetType(String))
> > wykszt.Columns.Add("nazwa_tytulu", GetType(String))
> > zatru = New System.Data.DataTable("zatr")
> > zatru.Columns.Add("od_data", GetType(date))
> > zatru.Columns.Add("do_data", GetType(date))
> > zatru.Columns.Add("nazwa_prac", GetType(String))
> > zatru.Columns.Add("nazwa_stan", GetType(String))
> > End sub
> > Sub Button2_Click(sender As Object, e As EventArgs)
> > row = wykszt.NewRow
> > row("od_data")=TextBox27.Text + "-01"
> > row("do_data")=TextBox28.Text + "-01"
> > row("nazwa_szkoly")=TextBox29.Text
> > row("nazwa_tytulu")=TextBox30.Text
> > wykszt.Rows.Add(row)
> > row = wykszt.NewRow
> > Mxdatagrid1.datasource=wykszt
> > Mxdatagrid1.databind
> > End Sub
> > Thanks
> > Pat

sorry i left behind that i have Dim row as System.Data.DataRow in my
declarations too
but exception is only when i post back and
on this line :
row = wykszt.NewRow

and a full stack :

Szczegy wyjtku: System.NullReferenceException: Odwoanie do obiektu nie
zostao ustawione na wystpienie obiektu.

Bd rda:

Wiersz 35: Sub Button2_Click(sender As Object, e As EventArgs)
Wiersz 36:
Wiersz 37: row = wykszt.NewRow
Wiersz 38: row("od_data")=TextBox27.Text + "-01"
Wiersz 39: row("do_data")=TextBox28.Text + "-01"

Plik rdowy: c:\inetpub\wwwroot\axell\forma.aspx Wiersz: 37

lad stosu:

[NullReferenceException: Odwoanie do obiektu nie zostao ustawione na
wystpienie obiektu.]
ASP.forma_aspx.Button2_Click(Object sender, EventArgs e) in
c:\inetpub\wwwroot\axell\forma.aspx:37
System.Web.UI.WebControls.Button.OnClick(EventArgs e) +108

System.Web.UI.WebControls.Button.System.Web.UI.IPo stBackEventHandler.RaisePo
stBackEvent(String eventArgument) +58
System.Web.UI.Page.RaisePostBackEvent(IPostBackEve ntHandler
sourceControl, String eventArgument) +18
System.Web.UI.Page.RaisePostBackEvent(NameValueCol lection postData) +33
System.Web.UI.Page.ProcessRequestMain() +1277

sorry for polish language

Thanks

Pat
In that case I agree with Marina.
You need to recreate your table upon each postback.
Right now you aren't doing that, so you can't add a row to a table that
doesn't exist, thus your error.
Remove the If statement in Page_Load.

--
I hope this helps,
Steve C. Orr, MCSD, MVP
http://Steve.Orr.net

> sorry i left behind that i have Dim row as System.Data.DataRow in my
> declarations too
> but exception is only when i post back and
> on this line :
> row = wykszt.NewRow
> and a full stack :
> Szczegy wyjtku: System.NullReferenceException: Odwoanie do obiektu nie
> zostao ustawione na wystpienie obiektu.
> Bd rda:
> Wiersz 35: Sub Button2_Click(sender As Object, e As EventArgs)
> Wiersz 36:
> Wiersz 37: row = wykszt.NewRow
> Wiersz 38: row("od_data")=TextBox27.Text + "-01"
> Wiersz 39: row("do_data")=TextBox28.Text + "-01"
>
> Plik rdowy: c:\inetpub\wwwroot\axell\forma.aspx Wiersz: 37
> lad stosu:
> [NullReferenceException: Odwoanie do obiektu nie zostao ustawione na
> wystpienie obiektu.]
> ASP.forma_aspx.Button2_Click(Object sender, EventArgs e) in
> c:\inetpub\wwwroot\axell\forma.aspx:37
> System.Web.UI.WebControls.Button.OnClick(EventArgs e) +108
> System.Web.UI.WebControls.Button.System.Web.UI.IPo stBackEventHandler.RaisePo
> stBackEvent(String eventArgument) +58
> System.Web.UI.Page.RaisePostBackEvent(IPostBackEve ntHandler
> sourceControl, String eventArgument) +18
> System.Web.UI.Page.RaisePostBackEvent(NameValueCol lection postData) +33
> System.Web.UI.Page.ProcessRequestMain() +1277
> sorry for polish language
> Thanks
> Pat