第三节 8下拉列表

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 _8下拉列表
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            //取得combox的几种方式
            MessageBox.Show(Convert.ToString(comboBox1.SelectedIndex));//索引
            MessageBox.Show(Convert.ToString(comboBox1.SelectedValue));
            MessageBox.Show(Convert.ToString(comboBox1.SelectedText));
            MessageBox.Show(Convert.ToString(comboBox1.SelectedItem)); //文本
        }

        private void button2_Click(object sender, EventArgs e)
        {
            string str1 = tb_start.Text;
            string str2 = tb_end.Text;
            int i1, i2;
            if (!int.TryParse(str1, out i1)) {
                MessageBox.Show("开始数值必须为整数!");
                return;
            }
            if (!int.TryParse(str2, out i2)) {
                MessageBox.Show("结束数值必须为整数!");
                return;
            }
            int sum = 0;

            switch (comboBox2.SelectedIndex) 
            {
                case 0://+
                    sum = i1 + i2;
                    break;
                case 1://-
                    sum = i1 - i2;
                    break;
                case 2://*
                    sum = i1 * i2;
                    break;
                case 3:// /
                    if (i2 == 0) {
                        MessageBox.Show("被除数不能为0!");
                        return;
                    }
                    sum = i1 / i2;
                    break;
                default:
                    throw new Exception("无法认别的计算符!");

            }
            tb_sum.Text = Convert.ToString(sum);
        }

        private void tb_private_SelectedIndexChanged(object sender, EventArgs e)
        {
            string str = Convert.ToString(tb_private.SelectedItem);
            tb_city.Items.Clear(); //清空tb_city中的所有元素

            if (str == "四川") 
            {
                tb_city.Items.Add("成都");
                tb_city.Items.Add("巴中");
                tb_city.Items.Add("达州");
            }
            else if (str == "江西") {
                tb_city.Items.Add("南昌");
                tb_city.Items.Add("九江");
            }
            else if (str == "安徽") {
                tb_city.Items.Add("黄山");
                tb_city.Items.Add("平湖");
            }
            //MessageBox.Show("显示");
        }
    }
}