Need help editing Customer Info in VB.net - vb.net

Question

I am trying to edit customers using my C# project to learn how to implement this code in VB.net. The project was successful in adding customers, but when it got to editing customers, things got a bit more complicated because I needed to get the id of the row selected and pass it to a string. I have the MainForm.vb which could open CustomerForm.vb when I click on 'Edit'. When CustomerForm.vb opens, it failed to show the customer's info. I am not sure if FillDataTable() function is necassary, I would like to know if there is an improvement to this.
CustomerForm.vb
Imports System.Data.SqlClient
Public Class CustomerForm
Private objConnection As SqlConnection
Public objDataTable As DataTable = New DataTable()
Public objSqlCommand As SqlCommand = New SqlCommand()
Public editMode As Boolean = False
Public id As String = ""
Public FName As String = ""
Public LName As String = ""
Public PhNumber As String = ""
Public ReadOnly Property Connection As SqlConnection
Get
Return Me.objConnection
End Get
End Property
Dim CS As String = ("server=CASHAMERICA;Trusted_Connection=yes;database=ProductsDatabase2; connection timeout=30")
Private Sub btnSave_Click(sender As Object, e As EventArgs) Handles btnSave.Click
Try
If editMode = False Then
If txtFirstName.Text = "" Then
MessageBox.Show("First Name Is required")
ElseIf txtLastName.Text = "" Then
MessageBox.Show("Last Name Is required")
Else
Dim con As New SqlConnection(CS)
con.Open()
Dim cmd As New SqlCommand("INSERT INTO Customers(FIrstName,LastName,PhoneNumber) VALUES(#FName, #LName, #PhNumber)", con)
cmd.Parameters.AddWithValue("#FName", txtFirstName.Text)
cmd.Parameters.AddWithValue("#LName", txtLastName.Text)
cmd.Parameters.AddWithValue("#PhNumber", txtPhoneNumber.Text)
cmd.ExecuteNonQuery()
MessageBox.Show("Customer has been added!")
con.Close()
End If
ElseIf editMode = True Then
If txtFirstName.Text = "" Then
MessageBox.Show("First Name Is required")
ElseIf txtLastName.Text = "" Then
MessageBox.Show("Last Name Is required")
Else
Dim con As New SqlConnection(CS)
con.Open()
Dim cmd As New SqlCommand("UPDATE Customers SET FIrstName = #FName, LastName = #LName, PhoneNumber = #PhNumber WHERE Id = #Id", con)
cmd.Parameters.AddWithValue("#Id", id)
cmd.Parameters.AddWithValue("#FName", txtFirstName.Text)
cmd.Parameters.AddWithValue("#LName", txtLastName.Text)
cmd.Parameters.AddWithValue("#PhNumber", txtPhoneNumber.Text)
cmd.ExecuteNonQuery()
MessageBox.Show("Customer has been edited.")
con.Close()
End If
End If
Catch ex As Exception
MessageBox.Show(Me, ex.Message, "Save Failed", MessageBoxButtons.OK, MessageBoxIcon.Error)
End Try
End Sub
Private Sub btnCancel_Click(sender As Object, e As EventArgs) Handles btnCancel.Click
Me.Close()
End Sub
Private Sub CustomerForm_Load(sender As Object, e As EventArgs) Handles MyBase.Load
If editMode = False Then
GetId()
Else
textId.Text = id
txtFirstName.Text = FName
txtLastName.Text = LName
txtPhoneNumber.Text = PhNumber
End If
End Sub
Private Sub GetId()
Dim con As New SqlConnection(CS)
con.Open()
Dim cmd As New SqlCommand("SELECT MAX(id)+1 FROM Customers")
textId.Text = FillDataTable().Rows(0)(0).ToString()
If textId.Text = "" Then
textId.Text = "1"
End If
End Sub
Public Property CommandText As String
Get
Return CommandText
End Get
Set(ByVal value As String)
CommandText = value
End Set
End Property
Public Sub OpenDBConnection()
objConnection = New SqlConnection(CS)
objConnection.Open()
End Sub
Public Sub CreateCommandObject()
objSqlCommand = objConnection.CreateCommand()
objSqlCommand.CommandText = CommandText
objSqlCommand.CommandType = CommandType.Text
End Sub
Public Function FillDataTable() As DataTable
objDataTable = New DataTable()
objSqlCommand.CommandText = CommandText
objSqlCommand.Connection = objConnection
objSqlCommand.CommandType = CommandType.Text
objDataTable.Load(objSqlCommand.ExecuteReader())
objConnection.Close()
Return objDataTable
End Function
Public Sub CloseConnection()
If objConnection IsNot Nothing Then objConnection.Close()
End Sub
End Class
MainForm.vb
Imports System.Windows.Forms.LinkLabel
Public Class MainForm
Private Sub ExitToolStripMenuItem_Click(sender As Object, e As EventArgs) Handles ExitToolStripMenuItem.Click
Me.Close()
End Sub
Private Sub AddToolStripMenuItem_Click(sender As Object, e As EventArgs) Handles AddToolStripMenuItem.Click
CustomerForm.ShowDialog()
End Sub
Private Sub AddToolStripMenuItem1_Click(sender As Object, e As EventArgs) Handles AddToolStripMenuItem1.Click
ProductForm.ShowDialog()
End Sub
Private Sub ViewProductsToolStripMenuItem_Click(sender As Object, e As EventArgs) Handles ViewProductsToolStripMenuItem.Click
ManageProductsForm.ShowDialog()
End Sub
Private Sub AboutToolStripMenuItem_Click(sender As Object, e As EventArgs) Handles AboutToolStripMenuItem.Click
AboutForm.Show()
End Sub
Private Sub MainForm_Load(sender As Object, e As EventArgs) Handles MyBase.Load
'TODO: This line of code loads data into the 'ProductsDatabase2DataSet1.Customers' table. You can move, or remove it, as needed.
Me.CustomersTableAdapter.Fill(Me.ProductsDatabase2DataSet1.Customers)
End Sub
Private Sub gridCustomers_MouseUp(ByVal sender As System.Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles gridCustomers.MouseUp
Try
Dim f As CustomerForm = New CustomerForm()
f.editMode = True
Dim rowIndex As Integer = gridCustomers.CurrentCell.RowIndex
f.id = gridCustomers.Rows(rowIndex).Cells("colId").Value.ToString()
f.FName = gridCustomers.Rows(rowIndex).Cells("colFirstName").Value.ToString()
f.LName = gridCustomers.Rows(rowIndex).Cells("colLastName").Value.ToString()
f.PhNumber = gridCustomers.Rows(rowIndex).Cells("colPhoneNumber").Value.ToString()
f.Show()
Catch ex As Exception
MessageBox.Show(ex.Message)
End Try
End Sub
Private Sub gridCustomers_CellContentClick(sender As Object, e As DataGridViewCellEventArgs) Handles gridCustomers.CellContentClick
Dim f As CustomerForm = New CustomerForm()
f.ShowDialog(Me)
f.editMode = True
End Sub
End Class
Error Message:
Customer Info not displayed:

Answer 1

As mentioned, it seems like you have several things potentially going on.
The first thing I would change is your public sql objects. You don't need them to be public. It also increases the chances for issues if you're using the same objects in multiple places.
SqlCommand, SqlConnection, and SqlDataAdapters can be immediately disposed of (in most cases) as soon as they are used.
One easy method to handling all of that is to throw everything inside of a USING block.
Dim sqlResult As New Datatable()
Using cn As New SqlConnection("Connection String here"),
cmd As New SqlCommand(sql, cn),
adapt As New SqlDataAdapter(cmd)
cn.Open()
'Handle stored procedure vs select options
If sql.Contains("SELECT") Then
cmd.CommandType = CommandType.Text
Else
cmd.CommandType = CommandType.StoredProcedure
End If
'If parameters passed, else comment out
cmd.Parameters.AddWithValue("#parameterName", parameterValue)
sqlResult = New DataTable(cmd.CommandText)
adapt.Fill(sqlResult)
End Using
Now all your objects are disposed of as soon as your datatable is filled.
*This example uses a datatable, but it is the same idea for anything interacting with sql objects.
If implemented, you may find out that some objects weren't being disposed of or initialized properly.
Another method for testing where things are going wrong is to query the states of the SQL objects before or around the error to see if something isn't set correctly or is uninitialized.