(深入.Net平台和C#编程)第六章.上机练习4.20170410

　　----------父类----------

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

namespace Lesson6_4
{
    /// <summary>
    /// 父类
    /// </summary>
    public class Operation
    {
        /// <summary>
        /// 添加属性
        /// </summary>
        public double NumberA { get; set; }

        public double NumberB { get; set; }

     

        /// <summary>
        /// 定义虚方法GenResult()，返回类型为double
        /// </summary>
        /// <returns></returns>
        public virtual double GetResult()
        {
            double result = 0;
            return result;
        }
    }
}

　　----------OperationAdd类----------

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

namespace Lesson6_4
{
    /// <summary>
    /// 实现加法类
    /// </summary>
    public class OperationAdd:Operation//调用父类
    {
        public override double GetResult()
        {
            double result = NumberA + NumberB;
            return result;
        }
        
    }

    /// <summary>
    /// 实现减法类
    /// </summary>
    public class OperationAn : Operation//调用父类
    {
        public override double GetResult()
        {
            double result = NumberA - NumberB;
            return result;
        }
    }

    /// <summary>
    /// 实现除法的类
    /// </summary>
    public class OperationDiv : Operation
    {
        public override double GetResult()
        {
            if (NumberB == 0)
            {
                throw new Exception("除数不能为0！");
            }
            double result = NumberA / NumberB;
            return result;
        }
    }

    /// 实现乘法的类
    /// </summary>
    public class OperationCheng : Operation
    {
        public override double GetResult()
        {
            if (NumberB == 0)
            {
                throw new Exception("除数不能为0！");
            }
            double result = NumberA * NumberB;
            return result;
        }
    }
}

　　----------FrmCalc类----------

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 Lesson6_4
{
    public partial class FrmCalc : Form
    {
        public FrmCalc()
        {
            InitializeComponent();
        }

        /// <summary>
        /// 单击"计算"按钮的响应
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void button1_Click(object sender, EventArgs e)
        {
            //判断文本是否为空
            if (string.IsNullOrEmpty(txtOne.Text.Trim()) || string.IsNullOrEmpty(txtTwo.Text.Trim()))
            {
                MessageBox.Show("操作数不能为空！", "提示");
                //设置焦点
                this.txtOne.Focus();
                this.txtTwo.Focus();
                return;
            }
            else
            {
                //设置符号
                try
                {
                    Operation opr = new Operation();
                    switch (this.cmdOper.SelectedItem.ToString().Trim())
                    {
                        case "+":
                            {
                                opr = new OperationAdd();
                                break;
                            }
                        case "-":
                            {
                                opr = new OperationAn();
                                break;
                            }
                        case "*":
                            {
                                opr = new OperationCheng();
                                break;
                            }
                        case "/":
                            {
                                opr = new OperationDiv();
                                break;
                            }
                    }
                    //计算参与计算的数据
                    opr.NumberA = double.Parse(this.txtOne.Text.Trim());
                    opr.NumberB = double.Parse(this.txtTwo.Text.Trim());
                    //计算
                    this.lbResult.Text = opr.GetResult().ToString();
                    this.lbResult.Visible = true;
                }
                catch (Exception ex)
                {

                    MessageBox.Show("发生错误！" + ex.Message);
                }
            }
        }

        /// <summary>
        /// 设置组合框默认选中
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void FrmCalc_Load(object sender, EventArgs e)
        {
            cmdOper.SelectedIndex = 0;
        }
    }
}