委托和事件练习之学校考试

就委托和事件，尝试一个作业，可参考前面的《老鼠出现引发的血案》。

这次我们就学生考试展开：老师下令考试，学生开始考试；学生宣布考完，老师就来收卷。怎么写？

using System;

namespace 委托与事件总结
{
    //定义委托
    public delegate void delegateFinishedExam(DateTime FinishedTime, Student student);
    public delegate void delegateStartExam(DateTime StartTime);

    public class Student
    {
        //定义事件，关联到委托
        public event delegateFinishedExam EventFinishExam;

        private string _name;

        //在构造中初始化成员(字段)变量
        public Student(string name)
        {
            this._name = name;
        }

        //答题的函数，开始答题
        public void BeginExam(DateTime BeginTime)
        {
            Console.WriteLine("\n时间为:" + BeginTime + " " + _name + "开始答题:...");
        }

        //答题完,引发完成考试事件
        public void EndExam()
        {
            Console.WriteLine();
            Console.WriteLine(this.ToString() + "答题完成.");
            EventFinishExam(DateTime.Now, this);
            //            EventFinishExam(this);
        }

        //重载基类的ToString方法,让ToString方法返回成员变量_name的值,即学生姓名
        public override string ToString()
        {
            return this._name;
        }
    }


    public class Teacher
    {
        //定义事件
        public event delegateStartExam EventStartExam;

        public Teacher() { }
        //引发开始测试事件的方法

        public void NotifyBeginExam()
        {
            EventStartExam(DateTime.Now);
        }

        //收考卷的方法.此处方法若写在入口类，须声明为静态方法
        public void AcceptPaper(DateTime AcceptTime, Student stu)
        {
            Console.WriteLine("\n收到{0} {1}的考卷.", stu.ToString(), AcceptTime);
        }
    }

    class RunApplication
    {
        static void Main(string[] args)
        {
            Teacher teacher = new Teacher();
            Student[] students = new Student[5];
            int i = 0;
            students[i++] = new Student("尹一");
            students[i++] = new Student("安二");
            students[i++] = new Student("张三");
            students[i++] = new Student("李四");
            students[i--] = new Student("王五");

            foreach (Student student in students)
            {
                //给每一个stus(学生)对象订阅tea(老师)对象的EventStartExam事件
                teacher.EventStartExam += new delegateStartExam(student.BeginExam);

                //给tea(老师)对象订阅每一个学生的完成答卷事件
             student.EventFinishExam += new delegateFinishedExam(teacher.AcceptPaper);
            }
            //tea(老师)对象通过函数NotifyBeginExam()引发EventStartExam事件
            teacher.NotifyBeginExam();
            Console.Write("请输入学生编号:");
            int num = int.Parse(Console.ReadLine());
            if (num < 0 || num > 4)
            {
                Console.WriteLine("您输入的编号非法!");
            }

            //stus[num]对象通过函数HandInPaper()引发EventFinishExam事件,完成考试
            students[num].EndExam();
            Console.ReadLine();//交给控制台(不调试)
        }
    }
}