//==========================================================================================
 //==================================Button functions========================================
 //==========================================================================================
 private void btAdd_Click(object sender, EventArgs e)
 {
     //validate inputs
     if (topicIDList.Contains(txtTopicID.Text)==false)
     {
         //create Topic object
         Topic t = new Topic();
         t.TopicID = this.txtTopicID.Text;
         t.TopicName = this.txtTopicName.Text;
         //insert topic object into Topic table
         BOTopic bot = new BOTopic();
         bool success = bot.Add(t);
         if (success)
         {
             MessageBox.Show("Add topic success!");
             loadTopicList();
         }
         else MessageBox.Show("Failed to add a topic!");
         txtTopicID.Clear();
         txtTopicName.Clear();
     }
     else
         MessageBox.Show("The topic code is exist");
 }