problem with checking null or empty value in detailsview

[bob]

Hi,

i want to check whether the textbox of the detailsview is not left empty, in
insert mode.
I did this:

Protected Sub DetailsView1_ItemInserting(ByVal sender As Object, ByVal e As
System.Web.UI.WebControls.DetailsViewInsertEventAr gs) Handles
DetailsView1.ItemInserting
Dim h As String
h = e.Values("myfield")
'If h = "" Then
If h Is Nothing Then
e.Cancel = True
Label1.Text = "may not be empty."
End If
End Sub

I tried two ways (with ="" and with is nothing), but in both cases, i always
get the label text and the event is always cancelled, even when i full some
value.

So, what's wrong with this code?

Thanks
Bob

[Mark Rae [MVP]]

"bob" <bo*@gh.vbwrote in message
news:uM**************@TK2MSFTNGP05.phx.gbl...

i want to check whether the textbox of the detailsview is not left empty,
in insert mode.
I did this:

Protected Sub DetailsView1_ItemInserting(ByVal sender As Object, ByVal e
As System.Web.UI.WebControls.DetailsViewInsertEventAr gs) Handles
DetailsView1.ItemInserting
Dim h As String
h = e.Values("myfield")
'If h = "" Then <== is this supposed to be commented?
If h Is Nothing Then
e.Cancel = True
Label1.Text = "may not be empty."
End If
End Sub

I tried two ways (with ="" and with is nothing), but in both cases, i
always get the label text and the event is always cancelled, even when i
full some value.

So, what's wrong with this code?

Firstly, you appear to have commented the line which I've highlighted, which
means that the corresponding End If must also be commented, otherwise the
code won't compile... I'm assuming you're using Option String...?

However, more fundamentally, a string variable can never really be a null
value, so it will never equate to Nothing in VB.NET...

Also, you appear not to be using any exception handling...
--
Mark Rae
ASP.NET MVP
http://www.markrae.net

[Mark Rae [MVP]]

"Mark Rae [MVP]" <ma**@markNOSPAMrae.netwrote in message
news:ee*************@TK2MSFTNGP02.phx.gbl...

code won't compile... I'm assuming you're using Option String...?

Apologies - I mean Option Strict...
--
Mark Rae
ASP.NET MVP
http://www.markrae.net

[Armin Zingler]

"bob" <bo*@gh.vbschrieb

Hi,

i want to check whether the textbox of the detailsview is not left
empty, in insert mode.
I did this:

Protected Sub DetailsView1_ItemInserting(ByVal sender As Object,
ByVal e As System.Web.UI.WebControls.DetailsViewInsertEventAr gs)
Handles
DetailsView1.ItemInserting
Dim h As String
h = e.Values("myfield")
'If h = "" Then
If h Is Nothing Then
e.Cancel = True
Label1.Text = "may not be empty."
End If
End Sub

I tried two ways (with ="" and with is nothing), but in both cases,
i always get the label text and the event is always cancelled, even
when i full some value.

So, what's wrong with this code?

First, you should enable Option Strict. The assignment

h = e.Values("myfield")

is not valid.

Then, you can examine the return value of e.Values. Maybe it is
DBNull.Value. If it is, you can do the comparison:

Dim Value as object
value = e.Values("myfield")

if value is dbnull.value then
'...
end if

If it's any other value, you will be able to see it in variable
'value', too.
Armin

[bob]

Thanks for replying ...
I tried this:

Protected Sub DetailsView1_ItemInserting(ByVal sender As Object, ByVal e As
System.Web.UI.WebControls.DetailsViewInsertEventAr gs) Handles
DetailsView1.ItemInserting
Dim h As Object
h = e.Values("myfield")
If h Is DBNull.Value Then
e.Cancel = True
Label1.Text = "may not be empty."
End If
End Sub

But now, the event is never cancelled and every value is accepted. In the
db, i see NULL when rhe input in the textbox was empty.
I conclude that 'h' is not DBNULL , but how to cancel the event when the
input is empty?

Thanks

"Armin Zingler" <az*******@freenet.deschreef in bericht
news:%2****************@TK2MSFTNGP05.phx.gbl...

"bob" <bo*@gh.vbschrieb

>Hi,

i want to check whether the textbox of the detailsview is not left
empty, in insert mode.
I did this:

Protected Sub DetailsView1_ItemInserting(ByVal sender As Object,
ByVal e As System.Web.UI.WebControls.DetailsViewInsertEventAr gs)
Handles
DetailsView1.ItemInserting
Dim h As String
h = e.Values("myfield")
'If h = "" Then
If h Is Nothing Then
e.Cancel = True
Label1.Text = "may not be empty."
End If
End Sub

I tried two ways (with ="" and with is nothing), but in both cases,
i always get the label text and the event is always cancelled, even
when i full some value.

So, what's wrong with this code?

First, you should enable Option Strict. The assignment

h = e.Values("myfield")

is not valid.

Then, you can examine the return value of e.Values. Maybe it is
DBNull.Value. If it is, you can do the comparison:

Dim Value as object
value = e.Values("myfield")

if value is dbnull.value then
'...
end if

If it's any other value, you will be able to see it in variable 'value',
too.
Armin

[Armin Zingler]

"bob" <bo*@gh.vbschrieb

Thanks for replying ...
I tried this:

Protected Sub DetailsView1_ItemInserting(ByVal sender As Object,
ByVal e As System.Web.UI.WebControls.DetailsViewInsertEventAr gs)
Handles
DetailsView1.ItemInserting
Dim h As Object
h = e.Values("myfield")
If h Is DBNull.Value Then
e.Cancel = True
Label1.Text = "may not be empty."
End If
End Sub

But now, the event is never cancelled and every value is accepted.
In the db, i see NULL when rhe input in the textbox was empty.
I conclude that 'h' is not DBNULL , but how to cancel the event when
the input is empty?

Use the built-in debugging features. Have you tried logging to debug
output? For example

Debug.Print(h.GetType.ToString)
Armin