how to remove System.NullReferenceException?

[ishanisircar]

hiya,

i am using vb and asp.net with sql server. when the vb page is run, a gridview is displayed. In the gridview when a link button is clicked, a calendar is displayed. i am using this code to displat the calendar. but i keep getting a System.NullRefe renceException. how can i remove this?

i get an error on this line of my code

CType(grTemp.FindControl("txtRenewTill"), TextBox).Visible = True

here is my code:

Protected Sub GridViewRenew_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles GridViewRenew.SelectedIndexChanged 
Dim grTemp As GridViewRow

Dim selected_date As DateTime 
selected_date = CalendarRenew.SelectedDate

For Each grTemp In GridViewRenew.Rows 
grTemp = GridViewRenew.SelectedRow

CalendarRenew.Visible = True

CType(grTemp.FindControl("txtRenewTill"), TextBox).Visible = True

Next

end sub 

Protected Sub CalendarRenew_SelectionChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles CalendarRenew.SelectionChanged 
Dim grTemp As GridViewRow

For Each grTemp In GridViewRenew.Rows 
grTemp = GridViewRenew.SelectedRow

CType(grTemp.FindControl("txtRenewTill"), TextBox).Text = CalendarRenew.SelectedDate 
Next

End Sub

------------------------

thanks a lot.

[Plater]

grTemp is not finding any control called "txtRenewTi ll" as a child control of itself. When FindControl failes it returns null. You should be checking for this.

[shweta123]

Hi,

You can do the following modification in the code in order to remove the Null Reference error:

 Dim txtTemp as new Textbox()
txtTemp =  CType(grTemp.FindControl("txtRenewTill"), TextBox)
If(IsdbNull(txtTemp)= False then 
    CType(grTemp.FindControl("txtRenewTill"), TextBox).Visible = True
End If

[Frinavale]

Hi,

You can do the following modification in the code in order to remove the Null Reference error:

Or you could just check it like so:

Dim txtTemp As TextBox = CType(grTemp.FindControl("txtRenewTill"), TextBox)

If txtTemp IsNot Nothing then 
   txtTemp.Visible = True
End If

I have a feeling that you're getting the Null Reference error because your TextBox ("txtRenewTill" ) is not in the template that the row is using.

Do you have a TextBox named "txtRenewTi ll" in your GridView's Edit Template?

If so, then you can only access it if the Edit Template is being used and you'll have to change your code to display the calendar when Editing a row instead of when a row is Selected.

-Frinny

[Plater]

I don't think isdbNull() would work in this case since it would be a real null (Nothing) and not a database null?

[Frinavale]

I don't think isdbNull() would work in this case since it would be a real null (Nothing) and not a database null?

Those were my thoughts too...I wasn't sure and that's why I recommending checking for "Nothing" instead of DBNull.