学习软件设计——C#练习（10）

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学习软件设计——C#练习（10）

2018年01月09日 ⁄ 综合 ⁄ 共 4171字 ⁄ 字号小中大 ⁄ 评论关闭

C#的事件机制是理解C#的一个难点，尤其对于初学者。我涉世不深，就站在初学者的角度上谈谈我的理解。

先说说，事件机制的情景背景，它就是在一段程序的上下文中。发生了一件事，我通知一个委托人，委托人按照已经定好的办法去处理。翻译成程序语言的表述就是（个人认为这是事件机制的核心）.

classA.event+=classB.delegataEventHandler(classC.method)

所以剩下的一切事情都围绕上面三样来做，事件，委托，办法。注意这三样东西可以来自不同的类，下面我以微软的一个例程作为讲解：

using System;

// FireEventArgs: a custom event inherited from EventArgs.

public class FireEventArgs: EventArgs {
    public FireEventArgs(string room,int ferocity) {
        this.room = room;
        this.ferocity = ferocity;
    }

// The fire event will have two pieces of information--
// 1) Where the fire is, and 2) how "ferocious" it is.

public string room;
public int ferocity;

} //end of class FireEventArgs

// Class with a function that creates the eventargs and initiates the event
public class FireAlarm {

// Events are handled with delegates, so we must establish a FireEventHandler
// as a delegate:

public delegate void FireEventHandler(object sender, FireEventArgs fe);
// Now, create a public event "FireEvent" whose type is our FireEventHandler delegate.

public event FireEventHandler FireEvent;

// This will be the starting point of our event-- it will create FireEventArgs,
// and then raise the event, passing FireEventArgs.

public void ActivateFireAlarm(string room,int ferocity) {

FireEventArgs fireArgs = new FireEventArgs(room, ferocity);

        // Now, raise the event by invoking the delegate. Pass in
        // the object that initated the event (this) as well as FireEventArgs.
        // The call must match the signature of FireEventHandler.

        FireEvent(this, fireArgs);
    }
}    // end of class FireAlarm

// Class which handles the event

class FireHandlerClass {

// Create a FireAlarm to handle and raise the fire events.

public FireHandlerClass(FireAlarm fireAlarm) {

        // Add a delegate containing the ExtinguishFire function to the class'
        // event so that when FireAlarm is raised, it will subsequently execute
        // ExtinguishFire.

fireAlarm.FireEvent += new FireAlarm.FireEventHandler(ExtinguishFire);
}

// This is the function to be executed when a fire event is raised.

void ExtinguishFire(object sender, FireEventArgs fe) {

Console.WriteLine("/nThe ExtinguishFire function was called by {0}.", sender.ToString());

// Now, act in response to the event.

        if (fe.ferocity < 2)
            Console.WriteLine("This fire in the {0} is no problem. I'm going to pour some water on it.", fe.room);
        else if (fe.ferocity < 5)
            Console.WriteLine("I'm using FireExtinguisher to put out the fire in the {0}.", fe.room);
        else
            Console.WriteLine("The fire in the {0} is out of control. I'm calling the fire department!", fe.room);
    }
}    //end of class FireHandlerClass

public class FireEventTest {
public staticvoid Main () {

// Create an instance of the class that will be firing an event.

        FireAlarm myFireAlarm = new FireAlarm();

        // Create an instance of the class that will be handling the event. Note that
        // it receives the class that will fire the event as a parameter.

        FireHandlerClass myFireHandler = new FireHandlerClass(myFireAlarm);

        //use our class to raise a few events and watch them get handled
        myFireAlarm.ActivateFireAlarm("Kitchen", 3);
        myFireAlarm.ActivateFireAlarm("Study", 1);
        myFireAlarm.ActivateFireAlarm("Porch", 5);

        return;

} //end of main

} // end of FireEventTest

以上这个火灾事件处理程序的关键就是三个地方：

火灾处理委托的定义：

public delegate void FireEventHandler(object sender, FireEventArgs fe);

火灾这件事发生的定义：

public event FireEventHandler FireEvent; 顺便说一下事件其实就是同签名的委托

在这个函数里面激发事件，即这事发生了

public void ActivateFireAlarm(string room,int ferocity) {

FireEventArgs fireArgs = new FireEventArgs(room, ferocity);

FireEvent(this, fireArgs);
}

火灾发生的处理办法：

void ExtinguishFire(object sender, FireEventArgs fe) {

        Console.WriteLine("/nThe ExtinguishFire function was called by {0}.", sender.ToString());
        if (fe.ferocity < 2)
            Console.WriteLine("This fire in the {0} is no problem. I'm going to pour some water on it.", fe.room);
        else if (fe.ferocity < 5)
            Console.WriteLine("I'm using FireExtinguisher to put out the fire in the {0}.", fe.room);
        else
            Console.WriteLine("The fire in the {0} is out of control. I'm calling the fire department!", fe.room);
    }
核心语句：把这三样东西关联起来：