using System;

using System.Collections.Generic;

using System.ComponentModel;

using System.Data;

using System.Drawing;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

using System.Windows.Forms;

namespace combox

{

    public partial class Form1 : Form

    {

        public Form1()

        {

            InitializeComponent();

        }

        private void button1_Click(object sender, EventArgs e)

        {

            //通过下拉框添加数据

            comboBox2.Items.Add("张三");

            comboBox2.Items.Add("李四");

            comboBox2.Items.Add("王五");

        }

        private void button2_Click(object sender, EventArgs e)

        {

            //清除成员

            comboBox2.Items.Clear();

        }

    }

}

using System;

using System.Collections.Generic;

using System.ComponentModel;

using System.Data;

using System.Drawing;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

using System.Windows.Forms;

namespace 日期选择器

{

    public partial class Form1 : Form

    {

        public Form1()

        {

            InitializeComponent();

        }       

        private void Form1_Load(object sender, EventArgs e)

        {

            //在程序加载的时候 将年份添加到下拉框当中

            //因为年份的加载到我们现在的时候，所以要先获得当前的年份

            int year = DateTime.Now.Year;

            for (int i = 1949; i <= year; i++)

            {

                cboYear.Items.Add(i + "年");

            }

        }

        /// <summary>

        /// 当年份发生该改变的时候 加载月份

        /// </summary>

        /// <param name="sender"></param>

        /// <param name="e"></param>

        private void cboYear_SelectedIndexChanged(object sender, EventArgs e)

        {

            cboMonth.Items.Clear();//在每次点击选择年份的时候，应该把上一次的月份清空，不然会出现重复现象

            //在点击年份下拉框选好之后，把月份加入

            for (int i = 1; i <=12; i++)

            {

                cboMonth.Items.Add(i + "月");

            }

        }

        /// <summary>

        /// 当月份发生改变的时候加载天数

        /// </summary>

        /// <param name="sender"></param>

        /// <param name="e"></param>

        private void cboMonth_SelectedIndexChanged(object sender, EventArgs e)

        {

            //在点击月份之前，清空天数

            cboDay.Items.Clear();

            //获取年份跟月份，以此来判断天数是多少

            int day = 0;

            string strYear = cboYear.SelectedItem.ToString().Split(new char[] { '年' }, StringSplitOptions.RemoveEmptyEntries)[0];

            string strMonth = cboMonth.SelectedItem.ToString().Split(new char[] { '月' }, StringSplitOptions.RemoveEmptyEntries)[0];

            int year = Convert.ToInt32(strYear);

            int month = Convert.ToInt32(strMonth);

            switch(month)

            {

                case 1:

                case 3:

                case 5:

                case 7:

                case 8:

                case 10:

                case 12:day = 31;

                    break;

                case 2:

                    if((year%400==0)||(year%4==0&&year%100!=0))

                    {

                        day = 29;

                    }

                    else

                    {

                        day = 28;

                    }

                    break;

                default:day = 30;

                    break;

            }

            for (int i = 1; i <= day; i++)

            {

                cboDay.Items.Add(i + "日");

            }

        }

    }

}