用C#制作有提示窗体的日程管理器。

以下为主窗体代码：

using System;
using System.Drawing;
using System.Collections;
using System.ComponentModel;
using System.Windows.Forms;
using System.Data;
using System.Timers;
using System.Data.OleDb;
namespace Calendar
{
 /// <summary>
 /// Form1 的摘要说明。
 /// </summary>
 public class Form1 : System.Windows.Forms.Form
 {
  private System.Windows.Forms.TabControl tabControl1;
  private System.Windows.Forms.TabPage first;
  private System.Windows.Forms.TabPage tabPage1;
  private System.Windows.Forms.Button button1;
  private System.Windows.Forms.Button button2;
  private System.Windows.Forms.Button button3;
  private System.Windows.Forms.Button button4;
  private System.Windows.Forms.Button button5;
  private System.Windows.Forms.TextBox textBox1;
  private System.Windows.Forms.TextBox textBox2;
  private System.Windows.Forms.Label label1;
  private System.Windows.Forms.Label label2;
  private System.Windows.Forms.Label label3;
  private System.Windows.Forms.GroupBox groupBox1;
  private System.Windows.Forms.TextBox textBox3;
  private System.Windows.Forms.TabPage tabPage2;
  private System.Windows.Forms.TabPage tabPage3;
  private System.Windows.Forms.Timer timer1;
  private System.Windows.Forms.TextBox textBox4;
  private System.Data.OleDb.OleDbConnection Myconn;
  private System.Data.OleDb.OleDbCommand Mycmd;
  private System.ComponentModel.IContainer components;

  public OleDbDataReader dr;
  public string info;
  private System.Windows.Forms.TextBox textBox5;
  private System.Windows.Forms.CheckedListBox checkedListBox1;
  private System.Windows.Forms.Label label4;
  private System.Windows.Forms.TextBox textBox6;
  private System.Data.OleDb.OleDbCommand insertcmd;
  public DateTime da;
  public Form1()
  {
   //
   // Windows 窗体设计器支持所必需的
   //
   InitializeComponent();

   //
   // TODO: 在 InitializeComponent 调用后添加任何构造函数代码
   //
  }

  /// <summary>
  /// 清理所有正在使用的资源。
  /// </summary>
  protected override void Dispose( bool disposing )
  {
   if( disposing )
   {
    if (components != null)
    {
     components.Dispose();
    }
   }
   base.Dispose( disposing );
  }

  #region Windows 窗体设计器生成的代码
  /// <summary>
  /// 设计器支持所需的方法 - 不要使用代码编辑器修改
  /// 此方法的内容。
  /// </summary>
  private void InitializeComponent()
  {
   this.components = new System.ComponentModel.Container();
   System.Resources.ResourceManager resources = new System.Resources.ResourceManager(typeof(Form1));
   this.tabControl1 = new System.Windows.Forms.TabControl();
   this.tabPage1 = new System.Windows.Forms.TabPage();
   this.textBox5 = new System.Windows.Forms.TextBox();
   this.groupBox1 = new System.Windows.Forms.GroupBox();
   this.textBox3 = new System.Windows.Forms.TextBox();
   this.label3 = new System.W