NullReferenceException when trying to fill an array

  • Thread starter Thread starter Fabio Papa
  • Start date Start date
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Fabio Papa

Hi,

I am fairly new to programming and and even newer to dotnet. I appoligise in advance if this is a dumb questions, and I would appreciate if you could answer it anyways. :)

I am writing a windows service wich sends emails to customers at a specific time. My app retrieves cities and the city's associated time from a database, waits until the specified time for each city and sends out the appropriate emails. Below is some code that is generating a NullReferenceException which I haven't been able to debug. Please help!

Friend Class RgsDbConnection

Private rgsConn As SqlConnection
Private goTimes() As Date
Private locales() As String
Private _numLocales As Integer

....

Private Sub GetLocalesAndTimes()

Dim cmd As SqlDataAdapter
Dim rsData As New DataSet
Dim i As Integer

'Get a list of all locales and their email/fax sending time
cmd = New SqlDataAdapter("SELECT zonename, EmailFaxTime " _
& "FROM dbo.tblzone", me.rgsConn)
cmd.Fill(rsData, "LocalesAndTimes")

'Get number of locales
me._numLocales = rsData.Tables("LocalesAndTimes").Rows.Count

For i = 0 To me._numLocales - 1
'fill array with locales
Dim log as EventLog = New EventLog()
Try
'This next line is the one that causes the error
Me.locales(i) = _
rsData.Tables("LocalesAndTimes").Rows(i).Item("zonename")
Catch e As Exception
log.WriteEntry("RGS Email & Fax Sender", _
rsData.Tables("LocalesAndTimes").Rows(i).Item("zonename").ToString())
log.WriteEntry("RGS Email & Fax Sender", e.ToString)
End Try
'fill array with sending times
' me.goTimes(i) = _
' rsData.Tables("LocalesAndTimes").Rows(i).Item("EmailFaxTime")
Next i
End Sub
....

End Class

In the "For...Next" block you will notice a "Try" block. Inside the try block
is the single line of code that is causing the problem.

You'll notice in the catch block I write to the application event log twice (for each iteration of the for...next block). When I look at the event log, there are two entries for every record in my db, one stating the zonename and one with the error, which reads:
"System.NullReferenceException: Object reference not set to an instance of an object.
at RgsEmailSenderSpace.RgsDbConnection.GetLocalesAndTimes()"

Thanks in advance for your help.


fabio
 
Try this:

If Not ISDBNULL(rsData.Tables("LocalesAndTimes").Rows(i).Item("zonename")
) Then
me.locales(1) = rsData.Tables("LocalesAndTimes").Rows(i).Item("zonename")

Or this:

Debug.Assert(Not IsDBNull(rsData.Tables("LocalesAndTimes").Rows(i).Item("zonename")
))

If the assertion fails, you have a null value. This link will also show you a possible method to deal with it http://www.knowdotnet.com/testsite/nullvalues.html



You can also IIF that statement with the same logic and give it a different value.
Hi,

I am fairly new to programming and and even newer to dotnet. I appoligise in advance if this is a dumb questions, and I would appreciate if you could answer it anyways. :)

I am writing a windows service wich sends emails to customers at a specific time. My app retrieves cities and the city's associated time from a database, waits until the specified time for each city and sends out the appropriate emails. Below is some code that is generating a NullReferenceException which I haven't been able to debug. Please help!

Friend Class RgsDbConnection

Private rgsConn As SqlConnection
Private goTimes() As Date
Private locales() As String
Private _numLocales As Integer

...

Private Sub GetLocalesAndTimes()

Dim cmd As SqlDataAdapter
Dim rsData As New DataSet
Dim i As Integer

'Get a list of all locales and their email/fax sending time
cmd = New SqlDataAdapter("SELECT zonename, EmailFaxTime " _
& "FROM dbo.tblzone", me.rgsConn)
cmd.Fill(rsData, "LocalesAndTimes")

'Get number of locales
me._numLocales = rsData.Tables("LocalesAndTimes").Rows.Count

For i = 0 To me._numLocales - 1
'fill array with locales
Dim log as EventLog = New EventLog()
Try
'This next line is the one that causes the error
Me.locales(i) = _
rsData.Tables("LocalesAndTimes").Rows(i).Item("zonename")
Catch e As Exception
log.WriteEntry("RGS Email & Fax Sender", _
rsData.Tables("LocalesAndTimes").Rows(i).Item("zonename").ToString())
log.WriteEntry("RGS Email & Fax Sender", e.ToString)
End Try
'fill array with sending times
' me.goTimes(i) = _
' rsData.Tables("LocalesAndTimes").Rows(i).Item("EmailFaxTime")
Next i
End Sub
...

End Class

In the "For...Next" block you will notice a "Try" block. Inside the try block
is the single line of code that is causing the problem.

You'll notice in the catch block I write to the application event log twice (for each iteration of the for...next block). When I look at the event log, there are two entries for every record in my db, one stating the zonename and one with the error, which reads:
"System.NullReferenceException: Object reference not set to an instance of an object.
at RgsEmailSenderSpace.RgsDbConnection.GetLocalesAndTimes()"

Thanks in advance for your help.


fabio
 
Fabio Papa said:
Private locales() As String
[...]
'This next line is the one that causes the error
Me.locales(i) = _
rsData.Tables("LocalesAndTimes").Rows(i).Item("zonename")
Click to expand...


You did not create an array of strings. Variable locales contains Nothing.
Use Redim to create an array.
 
Hi William, thanks for your help. However there are no nulls in the db (it's a test db with only five records that I have verified). Further, when i write the city to the event log (as in my catch block), or try to assign it to another variable (one that is not a member variable array), it works just fine (I can see the cities listed in the event log). Another piece to the puzzle is that the sdk documentation says this about the NullReferenceException exception:

"Note that applications throw the ArgumentNullException exception rather than the NullReferenceException exception discussed here. The following Microsoft intermediate language (MSIL) instructions throw NullReferenceException: ........"

From the little that I know about IL, it looks like the exception is being thrown by the stelem.ref instruction in my compiled code.


fabio
Try this:

If Not ISDBNULL(rsData.Tables("LocalesAndTimes").Rows(i).Item("zonename")
) Then
me.locales(1) = rsData.Tables("LocalesAndTimes").Rows(i).Item("zonename")

Or this:

Debug.Assert(Not IsDBNull(rsData.Tables("LocalesAndTimes").Rows(i).Item("zonename")
))

If the assertion fails, you have a null value. This link will also show you a possible method to deal with it http://www.knowdotnet.com/testsite/nullvalues.html



You can also IIF that statement with the same logic and give it a different value.
Hi,

I am fairly new to programming and and even newer to dotnet. I appoligise in advance if this is a dumb questions, and I would appreciate if you could answer it anyways. :)

I am writing a windows service wich sends emails to customers at a specific time. My app retrieves cities and the city's associated time from a database, waits until the specified time for each city and sends out the appropriate emails. Below is some code that is generating a NullReferenceException which I haven't been able to debug. Please help!

Friend Class RgsDbConnection

Private rgsConn As SqlConnection
Private goTimes() As Date
Private locales() As String
Private _numLocales As Integer

...

Private Sub GetLocalesAndTimes()

Dim cmd As SqlDataAdapter
Dim rsData As New DataSet
Dim i As Integer

'Get a list of all locales and their email/fax sending time
cmd = New SqlDataAdapter("SELECT zonename, EmailFaxTime " _
& "FROM dbo.tblzone", me.rgsConn)
cmd.Fill(rsData, "LocalesAndTimes")

'Get number of locales
me._numLocales = rsData.Tables("LocalesAndTimes").Rows.Count

For i = 0 To me._numLocales - 1
'fill array with locales
Dim log as EventLog = New EventLog()
Try
'This next line is the one that causes the error
Me.locales(i) = _
rsData.Tables("LocalesAndTimes").Rows(i).Item("zonename")
Catch e As Exception
log.WriteEntry("RGS Email & Fax Sender", _
rsData.Tables("LocalesAndTimes").Rows(i).Item("zonename").ToString())
log.WriteEntry("RGS Email & Fax Sender", e.ToString)
End Try
'fill array with sending times
' me.goTimes(i) = _
' rsData.Tables("LocalesAndTimes").Rows(i).Item("EmailFaxTime")
Next i
End Sub
...

End Class

In the "For...Next" block you will notice a "Try" block. Inside the try block
is the single line of code that is causing the problem.

You'll notice in the catch block I write to the application event log twice (for each iteration of the for...next block). When I look at the event log, there are two entries for every record in my db, one stating the zonename and one with the error, which reads:
"System.NullReferenceException: Object reference not set to an instance of an object.
at RgsEmailSenderSpace.RgsDbConnection.GetLocalesAndTimes()"

Thanks in advance for your help.


fabio
 
That worked! Thank you Armin.
Armin Zingler said:
Fabio Papa said:
Private locales() As String
[...]
'This next line is the one that causes the error
Me.locales(i) = _
rsData.Tables("LocalesAndTimes").Rows(i).Item("zonename")
Click to expand...


You did not create an array of strings. Variable locales contains Nothing.
Use Redim to create an array.
Click to expand...
 
redim your locals and goTimes arrays. Unless I am mistaken, they do
not automaticly do this

'Get number of locales
me._numLocales = rsData.Tables("LocalesAndTimes").Rows.Count
redim goTimes(_numlocals-1)
redim locales(_numlocals-1)
 
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