中文XML论坛--C#快餐

发信人: nice (春天), 信区: DotNET
标  题: C#快餐－13
发信站: BBS 水木清华站 (Thu Jul 26 02:17:04 2001)

Lesson 13. Events

Let's start with a simple event algorithm.
Data: John is a 3rd grade student.
Event: John gets a grade (A-F)
Who is affected?: Mom, dad, sister.
How are they affected?: Mom and dad are happy when the grade is good
(better than C) and upset otherwise.

Since John and his sister just had a fight, John's sister has an opposite
reaction to her parents'. Bellow is a simple program which illustrates John's
family reaction to his grades. Class Test is listening to all events of type
grade. Every time a new grade is received, class Test triggers an event.
Class Event sends a message to a class that is subscribed to the event. If no
class is subscribed, the event is not handled by the program.

using System;
public delegate void grade_event(string s);
class Event
{
    public event grade_event grade;//delegate grade is a member of Event
    public void trigger_event(string s)
    {
    if(grade!=null)
        grade(s);
    else Console.WriteLine("Event is not registered");
    }
}
class Test
{
    public static void catch_event(string s)
    {
        Console.WriteLine(" Grade event "+s+" is caught");
         if(s=="A"||s=="B"){
            Console.WriteLine("The mom and the Dad are happy with "+s);
            Console.WriteLine(" The sister is upset with "+s);
        }
         else if( s=="C" || s=="D" || s=="F"){
            Console.WriteLine(" The mom and the dad are upset with "+s);
            Console.WriteLine(" The sister is happy with "+s);
        }
         else
        Console.WriteLine("The mom, the dad and the sister cannot understand
teacher's handwriting");
    }
    public static void Main()
    {
        Event my_event=new Event();
        my_event.grade+=new grade_event(catch_event); //register grade with
catch_event
        my_event.trigger_event("A");
        my_event.trigger_event("B");
        my_event.trigger_event("abrakadabra");
        my_event.grade-=new grade_event(catch_event); //quit registration
        }
}

Several different classes can use the same event handler to subscribe to
messages. Here is another program which illustrates this point. This program
has a class Grade which sends messages about John's grades and class Health
which sends messages about his health.

using System;
public delegate void my_event(string s);
class Event
{
    public event my_event mevent;//delegate mevent is a member of Event
    public void trigger_event(string s)
    {
    if(mevent!=null)
        mevent(s);
    else Console.WriteLine("Event is not registered");
    }
}
class Grade
{
    public static void catch_event(string s)
    {
        Console.WriteLine("Grade event "+s+" is caught");
        if(s=="A"||s=="B"){
            Console.WriteLine("Mam and Dad are happy with "+s);
            Console.WriteLine("Sister is uppset with "+s);
        }
         else if(s=="C"||s=="D"||s=="F"){
            Console.WriteLine("Mam and Dad are uppset with "+s);
            Console.WriteLine("Sister is happy with "+s);
        }
         else
        Console.WriteLine("Mam, Dad and sister cannot understand teacher's h
andwriting");
    }
    public Grade()
    {
        Event test=new Event();
        test.mevent+=new my_event(catch_event); //register grade with catch_
event
        test.trigger_event("A");
        test.trigger_event("B");
        test.trigger_event("abrakadabra");
        test.mevent-=new my_event(catch_event); //quit registration
       }
}
class Health
{
    public static void catch_event(string s)
    {
        Console.WriteLine("Health event "+s+" is caught");
         if(s=="sick"||s=="ill"){
            Console.WriteLine("Mam and Dad and the sister are worried that J
ohn is"+s);
        }
    }
    public Health()
    {
        Event test=new Event();
        test.mevent+=new my_event(catch_event); //register grade with catch_
event
        test.trigger_event("sick");
        test.trigger_event("ill");
        test.trigger_event("abrakadabra");
        test.mevent-=new my_event(catch_event); //quit registration
    }
}
public class Test
{
    public static void Main()
    {
    Health t1=new Health();
    Grade t2=new Grade();
    }
}

We will see in the next lesson how events are handled by the Graphical User
Interface.

--

※ 修改:·walts 於 Jul 26 10:30:27 修改本文·[FROM: 166.111.142.118]
※ 来源:·BBS 水木清华站 smth.org·[FROM: 166.111.176.234]
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