timer控件、三级联动

timer控件：

实现时间日期自增长：

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace timer控件
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();

            label1.Text = DateTime.Now.ToString("yyyy年MM月dd日hh时mm分ss秒");
        }
        //计时器
        private void timer1_Tick(object sender, EventArgs e)
        {
            label1.Text = DateTime.Now.ToString("yyyy年MM月dd日hh时mm分ss秒");
        }
    }
}

抽奖设置，点击开始开始抽奖，开始按钮变为结束，点击结束，抽奖结束，结束按钮变为开始：

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace timer控件
{
    public partial class Form2 : Form
    {
        List<long> nu = new List<long>();
        Random r = new Random();

        public Form2()
        {
            InitializeComponent();
            nu.Add();
            nu.Add();
            nu.Add();
            nu.Add();
            nu.Add();

        }
        //抽奖
        bool s = false;
        private void button1_Click(object sender, EventArgs e)
        {
            if (s)//结束抽奖
            {
                button1.Text = "开始";
                s = false;
                timer1.Enabled = false;
            }
            else//开始抽奖
            {
                button1.Text = "停止";
                s = true;
                timer1.Enabled = true;
            }
        }

        private void timer1_Tick(object sender, EventArgs e)
        {
            label2.Text= nu[r.Next(,nu.Count)].ToString();
        }
    }
}

作弊：
在if结束抽奖中加一句代码：

label2.text="";

三级联动：

创建实体类：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace 三级联动.App_Code
{
    public class china
    {
        public string areacode { get; set; }
        public string areaname { get; set; }
        public string parentareacode { get; set; }

    }
}

创建数据访问类：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data.SqlClient;

namespace 三级联动.App_Code
{
    public class chinadata
    {
        SqlConnection conn = null;
        SqlCommand cmd = null;

        public chinadata()
        {
            conn = new SqlConnection("server=.;database=mydb;user=sa;pwd=123");
            cmd = conn.CreateCommand();
        }

        public List<china> select(string pcode)
        {
            List<china> clist = new List<china>();
            cmd.CommandText = "select*from ChinaStates where ParentAreaCode=@a";
            cmd.Parameters.Clear();
            cmd.Parameters.Add("@a",pcode);
            conn.Open();
            SqlDataReader dr = cmd.ExecuteReader();
            if (dr.HasRows)
            {
                while (dr.Read())
                {
                    china c = new china();
                    c.areacode = dr[].ToString();
                    c.areaname = dr[].ToString();
                    c.parentareacode = dr[].ToString();
                    clist.Add(c);
                }
            }
            conn.Close();
            return clist;
        }

    }
}

form1：使用selectedindexchanged事件，引用命名空间

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using 三级联动.App_Code;

namespace 三级联动
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();

            //绑定省
            comboBox1.DataSource = new chinadata().select("");
            comboBox1.DisplayMember = "areaname";
            comboBox1.ValueMember = "areacode";

            //绑定市
            comboBox2.DataSource = new chinadata().select(comboBox1.SelectedValue.ToString());
            comboBox2.DisplayMember = "areaname";
            comboBox2.ValueMember = "areacode";

            //绑定区
            comboBox3.DataSource = new chinadata().select(comboBox2.SelectedValue.ToString());
            comboBox3.DisplayMember = "areaname";
            comboBox3.ValueMember = "areacode";

        }

        private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
        {
　　　　　　　//绑定市跟随省移动
            comboBox2.DataSource = new chinadata().select(comboBox1.SelectedValue.ToString());
            comboBox2.DisplayMember = "areaname";
            comboBox2.ValueMember = "areacode";
        }

        private void comboBox2_SelectedIndexChanged(object sender, EventArgs e)
        {
　　　　　　　//绑定区跟随市移动
            comboBox3.DataSource = new chinadata().select(comboBox2.SelectedValue.ToString());
            comboBox3.DisplayMember = "areaname";
            comboBox3.ValueMember = "areacode";
        }
    }
}