Vb .net Error, No row in database greater than 0 - sql-server

Question

I am making a vb .net winform project that uses a sql server database. A user inputs the details of a person (firstName, lastName, company, contactNumber, etc.) visiting a factory into textboxes, hits the save details button, and this saves the data in the datatable. This works fine, the problem is the next part. The user is then redirected to another form where the input details are shown from the database. This works for the first record but not for any record input after that, I get an error that says "There is no row at position 'n'" and the following line of code is highlighted in the form_Load:
txtFirstName.Text = CStr(dtVisitorDetails.Rows(CInt(CDbl(txtIdNumber.Text) - 1)).Item(1))
It is telling me that any rows after row 0 are not there but I know they are because I have input them and they are showing up in the datatable in the sql server database manager.
I cannot sort this problem, any help with this would be greatly appreciated. I am attaching the rest of the code that's involved with this problem.
Thanks in advanced.
Private Sub previousVisitor_Load(sender As Object, e As EventArgs) Handles MyBase.Load
connectionString = "Data Source=.\SQLExpress;InitialCatalog=Visitors;" & _
"IntegratedSecurity=True;MultipleActiveResultSets=True"
sqlVisitorDetails = "SELECT * FROM visitorDetails WHERE idNumber=#idNumber"
sqlCon.Open()
sqlCmd = New SqlCommand(sqlVisitorDetails, sqlCon)
sqlCmd.Parameters.AddWithValue("#idNumber", txtIdNumber.Text)
dtVisitorDetails = loadDtVisitorDetails()
txtFirstName.Text = CStr(dtVisitorDetails.Rows(CInt(CDbl(txtIdNumber.Text) - 1)).Item(1))
txtLastName.Text = CStr(dtVisitorDetails.Rows(CInt(CDbl(txtIdNumber.Text) - 1)).Item(2))
txtCompany.Text = CStr(dtVisitorDetails.Rows(CInt(CDbl(txtIdNumber.Text) - 1)).Item(3))
txtContactNumber.Text = CStr(dtVisitorDetails.Rows(CInt(CDbl(txtIdNumber.Text) - 1)).Item(4))
txtCountryCode.Text = CStr(dtVisitorDetails.Rows(CInt(CDbl(txtIdNumber.Text) - 1)).Item(5))
txtEmail.Text = CStr(dtVisitorDetails.Rows(CInt(CDbl(txtIdNumber.Text) - 1)).Item(7))
sqlCmd.Dispose()
sqlCon.Close()
End Sub
Private Function loadDtVisitorDetails() As DataTable
Dim dtVisitorDetails As DataTable = Nothing
sqlVisitorDetails = "SELECT * FROM visitorDetails WHERE idNumber=" & txtIdNumber.Text
dtVisitorDetails = fillDtVisitorDetails(sqlVisitorDetails)
Return dtVisitorDetails
End Function
Public Function fillDtVisitorDetails(ByVal sqlVisitorDetails As String) As DataTable
Dim dtVisitorDetails As New DataTable
Dim da As New SqlDataAdapter
Dim conCmd As New SqlCommand
conCmd.CommandText = sqlVisitorDetails
da.SelectCommand = conCmd
da.SelectCommand.Connection = sqlCon
dtVisitorDetails.Columns.GetEnumerator()
da.Fill(dtVisitorDetails)
Return dtVisitorDetails
End Function

Answer 1

Since you can only have 1 row for each unique ID number, when you search and filter as WHERE idNumber = ID Number in form, you should get at most 1 record. That means the DataTable can have at most 1 row.
When you access the Rows of a DataTable like dt.Rows(ID), you are trying to access the row at position number ID in the collection of rows. Therefore, when you do dtVisitorDetails.Rows(CInt(CDbl(txtIdNumber.Text) - 1) for any value of ID number greater than 1, it will fail because that index simply does not exist in the table.
Instead, you should directly use dtVisitorDetails.Rows(0) to access the row. Since you have filtered by the ID Numberm you will only get the details for that person by doing so. Finally, remember to add a check for the row count in the table, so that if you search for an ID which has no records, there will not be an error in trying to retrieve from the table.
Pseudo-code:
If dtVisitorDetails.Rows.Count > 0
txtFirstName.Text = CStr(dtVisitorDetails.Rows(0).Item(1))
...
End If