Insert checked items in checkedlistbox to SQL database.

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
 

 try
            Dim connectionString As String = "Server=DESKTOP-V12PTAV ;Database=test ;User Id=sa ;Password=wills8877"
            Using conn As New SqlConnection(connectionString)
                conn.Open()
                Dim cmd as new System.Data.SqlCommand("insert into x (z) values (@z)",     conn) 
                cmd.Parameters.AddWithValue("@z", "")
                System.Data.SqlTransaction strns=conn.BeginTransaction()
                try
                    cmd.Transaction=strns
                    Dim itemChecked As Object
                    For Each itemChecked In CheckedListBox1.CheckedItems
                        Dim str As String
                        str = itemChecked.item("sem1").ToString
                        cmd.Parameters(0).value=str
                        cmd.ExecuteNonQuery
                        Label1.Text = str
                    Next
                    strns.Commit()
                Catch ex As Exception
                    strns.RollBack()
                    msgbox(ex.message)
                End Try
                strns.Dispose()
                cmd.dispose()
                conn.Close()
                conn.Dispose()
            Catch ex As Exception
                msgbox(ex.message)
            End Try
        End Using