Using block - scope issues - vb.net

Question

I am learning visual basic and OOP on the fly.
This piece of code displays the query results to a combo box on a form...
Dim c = System.Configuration.ConfigurationManager.ConnectionStrings("db").ToString()
Dim daDogs As New SqlDataAdapter ("select dog_type from humane_society with(nolock)",c)
Dim dtdogs As New DataTable
dadogs.Fill(dtdogs)
cboDogs.DataSource = dtdogs
cboDogs.DisplayMember = "dog_type"
when I change it to use a Using block, the combo box is blank
I think it is a scope issue, but I don't know how to fix it. Any productive suggestions would be greatly appreciated. Thanks!
Dim c = System.Configuration.ConfigurationManager.ConnectionStrings("db").ToString()
Using cDog As New SqlConnection(c)
Using cmd As New SqlCommand("select dog_type from humane_society with(nolock)",cDog)
cmd.CommandType = commandtype.Text
Using daDogs As New SqlDataAdapter(cmd)
Using dtDogs As New Datatable`enter code here`
daDogs.Fill(dtDogs)
' MsgBox(dtMunic.Rows(500).Field(of string)(0))
cboDogs.DataSource = dtDogs
cboDogs.DisplayMember = "dog_type"
End Using
End Using
End Using
End Using

Answer 1

Not sure what that message box is doing in your code. Remember that a message box halts the code until the user responds. You connection, among other things, is open while the code waits.
You are correct that items declared in a block are scoped to that block.
I have separated your database code from your user interface code.
You can save using blocks by adding a comma and combining more than one object in the block. Behaves the same, just makes the code a bit easier to read.
Private ConStr As String = System.Configuration.ConfigurationManager.ConnectionStrings("db").ToString() '"Your connection string"
Private Function GetDogData() As DataTable
Dim dt As New DataTable
Using cDog As New SqlConnection(ConStr),
cmd As New SqlCommand("select dog_type from humane_society with(nolock)", cDog)
cDog.Open()
Using reader = cmd.ExecuteReader
dt.Load(reader)
End Using
End Using
Return dt
End Function
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Dim dtDogs = GetDogData()
cboDogs.DataSource = dtDogs
cboDogs.DisplayMember = "dog_type"
End Sub