ช่วยดู Bug ให้หน่อยครับ จะขึ้นข้อความว่าConnection must be valid and open ซึ่งจะเป็นเฉพาะตอนที่เพิ่มแถวข้อมูลใหม่

Imports System.Data
Imports MySql.Data.MySqlClient
Public Class Form1
    Dim StrCon = "Server=127.0.0.1;user id=root;password=1234;Database=convb"
    Dim Con As New MySqlConnection(StrCon)
    Dim Da As New MySqlDataAdapter
    Dim DS As New DataSet
  Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Sql = "select * from student"
        Da.MissingSchemaAction = MissingSchemaAction.AddWithKey
        Da.SelectCommand = New MySqlCommand(Sql, Con)
        Try
            Da.Fill(DS, "std")
            GridShow.DataSource = DS.Tables("std")
            Obj = Me.BindingContext(DS.Tables("std"))
            Call Btn_Status(True)
            Call ShowData(Obj.Position)
        Catch ex As Exception
            MessageBox.Show(ex.Message)
        End Try
    End Sub
Private Sub BtnSave_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles BtnSave.Click
        Dim Cb As New MySqlCommandBuilder(Da)
        Dim Dr_Save As DataRow = Nothing

        If ChkBtn = "add" Then
            Sql = "select * from student where std_id='" & TxtId.Text & "'"
            Da.MissingSchemaAction = MissingSchemaAction.AddWithKey
            Da.SelectCommand = New MySqlCommand(Sql, Con)
            Try
                Da.Fill(DS, "chk")
                If DS.Tables("chk").Rows.Count > 0 Then
                    MessageBox.Show("รหัส " & TxtId.Text & " มีอยู่แล้ว", "รหัสซ้ำ")
                    DS.Tables("chk").Clear() : Exit Sub
                End If
            Catch ex As Exception
                MessageBox.Show(ex.Message)
            End Try
            Dr_Save = DS.Tables("std").NewRow
            With Dr_Save
                .BeginEdit()
                .Item("std_id") = TxtId.Text
                .Item("std_fname") = TxtFName.Text
                .Item("std_lname") = TxtLName.Text
                .EndEdit()
            End With
            DS.Tables("std").Rows.Add(Dr_Save)
            Da.InsertCommand = Cb.GetInsertCommand
        ElseIf ChkBtn = "edit" Then
            Dr_Save = DS.Tables("std").Rows.Find(TxtId.Text)
            With Dr_Save
                .BeginEdit()
                .Item("std_fname") = TxtFName.Text
                .Item("std_lname") = TxtLName.Text
                .EndEdit()
                Da.UpdateCommand = Cb.GetUpdateCommand
            End With
        End If
        Da.Update(DS.Tables("std"))
        DS.Tables("std").AcceptChanges()
        Call Btn_Status(True)
    End Sub