C#中委托，事件理解入门

l 导论

l 什么是委托

l 事件的理解

l 事件关键字

l 最后

导论

在学习C#中的委托和事件过程中，我读了许多文章来理解他们二者究竟是怎么一回事，以及如何使用他们，现在我将整个的理解过程陈述以下，我学到的每一方面，恐怕也是你们需要掌握的：-）。

什么是委托？

委托和事件这两个概念是完全配合的。委托仅仅是函数指针，那就是说，它能够引用函数，通过传递地址的机制完成。委托是一个类，当你对它实例化时，要提供一个引用函数，将其作为它构造函数的参数。

每一个委托都有自己的签名，例如：Delegate int SomeDelegate(string s, bool b);是一个委托申明，在这里，提及的签名，就是说SomeDelegate 这个委托有 string 和 bool 类型的形参，返回一个int 类型。

上面提及的：当你对委托实例化时，要提供一个引用函数，将其作为它构造函数的参数。这里要注意了：被引用的这个函数必须和委托有相同的签名。

看下面的函数：

private int SomeFunction(string str, bool bln){...}

你可以把这个函数传给SomeDelegate的构造函数，因为他们有相似的签名（in other words，他们都有相同的形参类型和个数，并且返回相同的数据类型）。

SomeDelegate sd = new SomeDelegate(SomeFunction);

sd 引用了 SomeFunction，也就是说，SomeFunction已被sd所登记注册，如果你调用 sd，SomeFunction 这个函数也会被调用，记住：我所说 SomeFunction的含义，后面，我们会用到它。

现在，你应该知道如何使用委托了，让我们继续理解事件之旅……

事件的理解

我们知道，在C#中：

l 按钮（Button）就是一个类，当我们单击它时，就触发一次click事件。

l 时钟（Timer）也是一个类，每过一毫秒，就触发一次tick事件。

让我们通过一个例子来学习，假定有这样的情节：

现在有一个Counter的类，它有一个方法 CountTo(int countTo, int reachableNum)，该方法表示：在指定的时间段内（0~~countTo），当到达指定的时间点reachableNum时，就触发一次NumberReached事件。

它还有一个事件：NumberReached，事件是委托类型的变量。意思是：如果给事件命名，用event关键字和要使用的委托类型申明它即可，如下所示：

public event NumberReachedEventHandler NumberReached;

在上面的申明中，NumberReachedEventHandle 仅是一个委托，更确切的表示应该是：NumberReachedDelegate。但是微软从不这样认为MouseDelegate或者PaintDelegate，，而是称谓：MouseEventHandler 或者 PaintEventHandler。所以

NumberReachedEventHandler 比NumberReachedDelegate听起来更方便一些，OK?好了，让我们继续，现在你知道了，在我们声明事件之前，需要象下面这样的形式来定义委托：

public delegate void NumberReachedEventHandler(object sender, NumberReachedEventArgs e);

现在声明的委托 NumberReachedEventHandle，它有一个void 返回值，和object，NumberReachedEventArgs两个形参。就像我们在第一节中强调的那样，当实例化委托时，作为实参传入的函数也必须拥有和委托同样的签名。

在你的代码中，你是否用过PaintEventArgs 或者 MouseEventArgs来确定鼠标的移动位置？是否在触发Paint事件的对象中用过Graphics 属性？实际上，为用户提供数据的类都是继承于System.EventArgs类，就是我们常说的事件参数类，如果事件不提供参数，就不定义该类。在我们的例子中，我们通过下面的类提供预期的时间点。

public class NumberReachedEventArgs : EventArgs

{

private int _reached;

public NumberReachedEventArgs(int num)

{

this._reached = num;

}

public int ReachedNumber

{

get

{

return _reached;

}

好，有了前面的介绍，让我们到Counter类里面看看：

namespace Events

{

public delegate void NumberReachedEventHandler(object sender,

NumberReachedEventArgs e);

/// <summary>

/// Summary description for Counter.

/// </summary>

public class Counter

{

public event NumberReachedEventHandler NumberReached;

public Counter()

{

// TODO: Add constructor logic here

}

public void CountTo(int countTo, int reachableNum)

{

if(countTo < reachableNum)

throw new ArgumentException(

"reachableNum should be less than countTo");

for(int ctr=0;ctr<=countTo;ctr++)

{

if(ctr == reachableNum)

{

NumberReachedEventArgs e = new NumberReachedEventArgs(

reachableNum);

OnNumberReached(e);

return;//don't count any more

}

protected virtual void OnNumberReached(NumberReachedEventArgs e)

{

if(NumberReached != null)

{

NumberReached(this, e);//Raise the event

}

在Counter中，如果到达指定的时间点，就触发一次事件，有以下几个方面需要注意：

l 通过调用NumberReached（它是NumberReachedEventHandler委托的实例）来完成一次触发事件。

NumberReached(this, e); 通过这种方式，可以调用所有的注册函数。

l 通过 NumberReachedEventArgs e = new NumberReachedEventArgs(reachableNum); 为所有的注册函数提供事件数据。

l 看了上面的代码，你可能要问了：为什么我们直接用 OnNumberReached(NumberReachedEventArgs e)方法来调用NumberReached（this，e），而不用下面的代码呢？

if(ctr == reachableNum)

{

NumberReachedEventArgs e = new NumberReachedEventArgs(reachableNum);

//OnNumberReached(e);

if(NumberReached != null)

{

NumberReached(this, e);//Raise the event

}

return;//don't count any more

}

这个问题问得很好，那就让我们再看一下OnNumberReached 签名：

protected virtual void OnNumberReached(NumberReachedEventArgs e)

①你也明白关键字protected限定了只有从该类继承的类才能调用该类中的所有方法。

②关键字 virtual 表明了在继承类中可以重写该方法。

这两点非常有用，假设你在写一个从Counter继承而来的类，通过重写OnNumberReached 方法，你可以在事件触发之前，进行一次其他的工作。

protected override void OnNumberReached(NumberReachedEventArgs e)

{

//Do additional work

base.OnNumberReached(e);

}

注意：如果你没有调用base.OnNumberReached(e), 那么从不会触发这个事件！在你继承该类而想剔出它的一些其他事件时，使用该方式是非常有用的。

l 还要注意到：委托 NumberReachedEventHandler 是在类定义的外部，命名空间内定义的，对所有类来说是可见的。

好，该我们来实际操作使用Counter类了。

在我们简单的应用程序中，我们有两个文本框，分别是：txtCountTo和txtReachable：

下面是btnRun的click事件：

private void btnRun_Click(object sender, System.EventArgs e)

{

if(txtCountTo.Text == "" || txtReachable.Text=="")

return;

oCounter.CountTo(Convert.ToInt32(txtCountTo.Text), Convert.ToInt32(txtReachable.Text));

}

private void oCounter_NumberReached(object sender, NumberReachedEventArgs e)

{

MessageBox.Show("Reached: " + e.ReachedNumber.ToString());

}

初始化事件处理的语法如下：

oCounter = new Counter();

oCounter.NumberReached += new NumberReachedEventHandler(oCounter_NumberReached);

现在你明白了你刚才所做的一切，仅仅初始化 NumberReachedEventHandler 委托类型的对象（就像你实例化其他对象一样），注意到 oCounter_NumberReached 方法的签名与我前面提到的相似。

还要注意我们用的是+= 而不是=；这是因为委托是特殊的对象，它可以引用多个对象（在这里是指它可以引用多个函数）。For example 如果有另外一个

和oCounter_NumberReached一样具有相同签名的函数oCounter_NumberReached2，这两个函数都可以被引用：

oCounter = new Counter();

oCounter.NumberReached += new NumberReachedEventHandler(oCounter_NumberReached);

oCounter.NumberReached += new NumberReachedEventHandler(oCounter_NumberReached2);

现在，触发一个事件后，上面两个函数被依次调用。

视情况而定，如果你想让oCounter_NumberReached2在NumberReached事件发生后不再被调用，可以简单地这样写：oCounter.NumberReached -= new NumberReachedEventHandler(oCounter_NumberReached2);

最后

让我们看一下完整的源代码,以供参考：

Form1.cs

using System;

using System.Drawing;

using System.Collections;

using System.ComponentModel;

using System.Windows.Forms;

using System.Data;

namespace Events

{

/**//// <summary>

/// Summary description for Form1.

/// </summary>

public class Form1 : System.Windows.Forms.Form

{

Counter oCounter = null;

private System.Windows.Forms.Button cmdRun;

private System.Windows.Forms.TextBox txtReachable;

private System.Windows.Forms.TextBox txtCountTo;

private System.Windows.Forms.Label label1;

private System.Windows.Forms.Label label2;

private System.Windows.Forms.Button btnRemoveDelegate;

/**//// <summary>

/// Required designer variable.

/// </summary>

private System.ComponentModel.Container components = null;

public Form1()

{

// Required for Windows Form Designer support

InitializeComponent();

// TODO: Add any constructor code after InitializeComponent call

oCounter = new Counter();

oCounter.NumberReached += new NumberReachedEventHandler(oCounter_NumberReached);

oCounter.NumberReached += new NumberReachedEventHandler(oCounter_NumberReached2);

}

/**//// <summary>

/// Clean up any resources being used.

/// </summary>

protected override void Dispose( bool disposing )

{

if( disposing )

{

if (components != null)

{

components.Dispose();

}

base.Dispose( disposing );

}

Windows Form Designer generated code#region Windows Form Designer generated code

/**//// <summary>

/// Required method for Designer support - do not modify

/// the contents of this method with the code editor.

/// </summary>

private void InitializeComponent()

{

this.cmdRun = new System.Windows.Forms.Button();

this.txtReachable = new System.Windows.Forms.TextBox();

this.txtCountTo = new System.Windows.Forms.TextBox();

this.label1 = new System.Windows.Forms.Label();

this.label2 = new System.Windows.Forms.Label();

this.btnRemoveDelegate = new System.Windows.Forms.Button();

this.SuspendLayout();

// cmdRun

this.cmdRun.Location = new System.Drawing.Point(16, 72);

this.cmdRun.Name = "cmdRun";

this.cmdRun.Size = new System.Drawing.Size(48, 23);

this.cmdRun.TabIndex = 2;

this.cmdRun.Text = "Run";

this.cmdRun.Click += new System.EventHandler(this.cmdRun_Click);

// txtReachable

this.txtReachable.Location = new System.Drawing.Point(144, 40);

this.txtReachable.Name = "txtReachable";

this.txtReachable.Size = new System.Drawing.Size(56, 20);

this.txtReachable.TabIndex = 1;

this.txtReachable.Text = "";

// txtCountTo

this.txtCountTo.Location = new System.Drawing.Point(144, 16);

this.txtCountTo.Name = "txtCountTo";

this.txtCountTo.Size = new System.Drawing.Size(56, 20);

this.txtCountTo.TabIndex = 0;

this.txtCountTo.Text = "";

// label1

this.label1.AutoSize = true;

this.label1.Location = new System.Drawing.Point(16, 16);

this.label1.Name = "label1";

this.label1.Size = new System.Drawing.Size(51, 13);

this.label1.TabIndex = 3;

this.label1.Text = "Count To";

// label2

this.label2.AutoSize = true;

this.label2.Location = new System.Drawing.Point(16, 40);

this.label2.Name = "label2";

this.label2.Size = new System.Drawing.Size(99, 13);

this.label2.TabIndex = 4;

this.label2.Text = "Reach this number";

// btnRemoveDelegate

this.btnRemoveDelegate.Location = new System.Drawing.Point(16, 104);

this.btnRemoveDelegate.Name = "btnRemoveDelegate";

this.btnRemoveDelegate.Size = new System.Drawing.Size(168, 23);

this.btnRemoveDelegate.TabIndex = 5;

this.btnRemoveDelegate.Text = "Remove second handler";

this.btnRemoveDelegate.Click += new System.EventHandler(this.btnRemoveDelegate_Click);

// Form1

this.AutoScaleBaseSize = new System.Drawing.Size(5, 13);

this.ClientSize = new System.Drawing.Size(224, 134);

this.Controls.AddRange(new System.Windows.Forms.Control[]

{

this.btnRemoveDelegate,

this.label2,

this.label1,

this.txtCountTo,

this.txtReachable,

this.cmdRun});

this.Name = "Form1";

this.Text = "Events";

this.ResumeLayout(false);

}

#endregion

/**//// <summary>

/// The main entry point for the application.

/// </summary>

[STAThread]

static void Main()

{

Application.Run(new Form1());

}

private void btnRun_Click(object sender, System.EventArgs e)

{

if(txtCountTo.Text == "" || txtReachable.Text=="")

return;

oCounter.CountTo(Convert.ToInt32(txtCountTo.Text), Convert.ToInt32(txtReachable.Text));

}

private void oCounter_NumberReached(object sender, NumberReachedEventArgs e)

{

MessageBox.Show("Reached: " + e.ReachedNumber.ToString());

}

private void oCounter_NumberReached2(object sender, NumberReachedEventArgs e)

{

MessageBox.Show("Reached2: " + e.ReachedNumber.ToString());

}

private void btnRemoveDelegate_Click(object sender, System.EventArgs e)

{

oCounter.NumberReached -= new NumberReachedEventHandler(oCounter_NumberReached2);

oCounter.CountTo(Convert.ToInt32(txtCountTo.Text), Convert.ToInt32(txtReachable.Text));

}

using System;

using System.Drawing;

using System.Collections;

using System.ComponentModel;

using System.Windows.Forms;

using System.Data;

namespace Events

{

/**//// <summary>

/// Summary description for Form1.

/// </summary>

public class Form1 : System.Windows.Forms.Form

{

Counter oCounter = null;

private System.Windows.Forms.Button cmdRun;

private System.Windows.Forms.TextBox txtReachable;

private System.Windows.Forms.TextBox txtCountTo;

private System.Windows.Forms.Label label1;

private System.Windows.Forms.Label label2;

private System.Windows.Forms.Button btnRemoveDelegate;

/**//// <summary>

/// Required designer variable.

/// </summary>

private System.ComponentModel.Container components = null;

public Form1()

{

// Required for Windows Form Designer support

InitializeComponent();

// TODO: Add any constructor code after InitializeComponent call

oCounter = new Counter();

oCounter.NumberReached += new NumberReachedEventHandler(oCounter_NumberReached);

oCounter.NumberReached += new NumberReachedEventHandler(oCounter_NumberReached2);

}

/**//// <summary>

/// Clean up any resources being used.

/// </summary>

protected override void Dispose( bool disposing )

{

if( disposing )

{

if (components != null)

{

components.Dispose();

}

base.Dispose( disposing );

}

Windows Form Designer generated code#region Windows Form Designer generated code

/**//// <summary>

/// Required method for Designer support - do not modify

/// the contents of this method with the code editor.

/// </summary>

private void InitializeComponent()

{

this.cmdRun = new System.Windows.Forms.Button();

this.txtReachable = new System.Windows.Forms.TextBox();

this.txtCountTo = new System.Windows.Forms.TextBox();

this.label1 = new System.Windows.Forms.Label();

this.label2 = new System.Windows.Forms.Label();

this.btnRemoveDelegate = new System.Windows.Forms.Button();

this.SuspendLayout();

// cmdRun

this.cmdRun.Location = new System.Drawing.Point(16, 72);

this.cmdRun.Name = "cmdRun";

this.cmdRun.Size = new System.Drawing.Size(48, 23);

this.cmdRun.TabIndex = 2;

this.cmdRun.Text = "Run";

this.cmdRun.Click += new System.EventHandler(this.cmdRun_Click);

// txtReachable

this.txtReachable.Location = new System.Drawing.Point(144, 40);

this.txtReachable.Name = "txtReachable";

this.txtReachable.Size = new System.Drawing.Size(56, 20);

this.txtReachable.TabIndex = 1;

this.txtReachable.Text = "";

// txtCountTo

this.txtCountTo.Location = new System.Drawing.Point(144, 16);

this.txtCountTo.Name = "txtCountTo";

this.txtCountTo.Size = new System.Drawing.Size(56, 20);

this.txtCountTo.TabIndex = 0;

this.txtCountTo.Text = "";

// label1

this.label1.AutoSize = true;

this.label1.Location = new System.Drawing.Point(16, 16);

this.label1.Name = "label1";

this.label1.Size = new System.Drawing.Size(51, 13);

this.label1.TabIndex = 3;

this.label1.Text = "Count To";

// label2

this.label2.AutoSize = true;

this.label2.Location = new System.Drawing.Point(16, 40);

this.label2.Name = "label2";

this.label2.Size = new System.Drawing.Size(99, 13);

this.label2.TabIndex = 4;

this.label2.Text = "Reach this number";

// btnRemoveDelegate

this.btnRemoveDelegate.Location = new System.Drawing.Point(16, 104);

this.btnRemoveDelegate.Name = "btnRemoveDelegate";

this.btnRemoveDelegate.Size = new System.Drawing.Size(168, 23);

this.btnRemoveDelegate.TabIndex = 5;

this.btnRemoveDelegate.Text = "Remove second handler";

this.btnRemoveDelegate.Click += new System.EventHandler(this.btnRemoveDelegate_Click);

// Form1

this.AutoScaleBaseSize = new System.Drawing.Size(5, 13);

this.ClientSize = new System.Drawing.Size(224, 134);

this.Controls.AddRange(new System.Windows.Forms.Control[]

{

this.btnRemoveDelegate,

this.label2,

this.label1,

this.txtCountTo,

this.txtReachable,

this.cmdRun});

this.Name = "Form1";

this.Text = "Events";

this.ResumeLayout(false);

}

#endregion

/**//// <summary>

/// The main entry point for the application.

/// </summary>

[STAThread]

static void Main()

{

Application.Run(new Form1());

}

private void btnRun_Click(object sender, System.EventArgs e)

{

if(txtCountTo.Text == "" || txtReachable.Text=="")

return;

oCounter.CountTo(Convert.ToInt32(txtCountTo.Text), Convert.ToInt32(txtReachable.Text));

}

private void oCounter_NumberReached(object sender, NumberReachedEventArgs e)

{

MessageBox.Show("Reached: " + e.ReachedNumber.ToString());

}

private void oCounter_NumberReached2(object sender, NumberReachedEventArgs e)

{

MessageBox.Show("Reached2: " + e.ReachedNumber.ToString());

}

private void btnRemoveDelegate_Click(object sender, System.EventArgs e)

{

oCounter.NumberReached -= new NumberReachedEventHandler(oCounter_NumberReached2);

oCounter.CountTo(Convert.ToInt32(txtCountTo.Text), Convert.ToInt32(txtReachable.Text));

}

using System;

using System.Drawing;

using System.Collections;

using System.ComponentModel;

using System.Windows.Forms;

using System.Data;

namespace Events

{

/**//// <summary>

/// Summary description for Form1.

/// </summary>

public class Form1 : System.Windows.Forms.Form

{

Counter oCounter = null;

private System.Windows.Forms.Button cmdRun;

private System.Windows.Forms.TextBox txtReachable;

private System.Windows.Forms.TextBox txtCountTo;

private System.Windows.Forms.Label label1;

private System.Windows.Forms.Label label2;

private System.Windows.Forms.Button btnRemoveDelegate;

/**//// <summary>

/// Required designer variable.

/// </summary>

private System.ComponentModel.Container components = null;

public Form1()

{

// Required for Windows Form Designer support

InitializeComponent();

// TODO: Add any constructor code after InitializeComponent call

oCounter = new Counter();

oCounter.NumberReached += new NumberReachedEventHandler(oCounter_NumberReached);

oCounter.NumberReached += new NumberReachedEventHandler(oCounter_NumberReached2);

}

/**//// <summary>

/// Clean up any resources being used.

/// </summary>

protected override void Dispose( bool disposing )

{

if( disposing )

{

if (components != null)

{

components.Dispose();

}

base.Dispose( disposing );

}

Windows Form Designer generated code#region Windows Form Designer generated code

/**//// <summary>

/// Required method for Designer support - do not modify

/// the contents of this method with the code editor.

/// </summary>

private void InitializeComponent()

{

this.cmdRun = new System.Windows.Forms.Button();

this.txtReachable = new System.Windows.Forms.TextBox();

this.txtCountTo = new System.Windows.Forms.TextBox();

this.label1 = new System.Windows.Forms.Label();

this.label2 = new System.Windows.Forms.Label();

this.btnRemoveDelegate = new System.Windows.Forms.Button();

this.SuspendLayout();

// cmdRun

this.cmdRun.Location = new System.Drawing.Point(16, 72);

this.cmdRun.Name = "cmdRun";

this.cmdRun.Size = new System.Drawing.Size(48, 23);

this.cmdRun.TabIndex = 2;

this.cmdRun.Text = "Run";

this.cmdRun.Click += new System.EventHandler(this.cmdRun_Click);

// txtReachable

this.txtReachable.Location = new System.Drawing.Point(144, 40);

this.txtReachable.Name = "txtReachable";

this.txtReachable.Size = new System.Drawing.Size(56, 20);

this.txtReachable.TabIndex = 1;

this.txtReachable.Text = "";

// txtCountTo

this.txtCountTo.Location = new System.Drawing.Point(144, 16);

this.txtCountTo.Name = "txtCountTo";

this.txtCountTo.Size = new System.Drawing.Size(56, 20);

this.txtCountTo.TabIndex = 0;

this.txtCountTo.Text = "";

// label1

this.label1.AutoSize = true;

this.label1.Location = new System.Drawing.Point(16, 16);

this.label1.Name = "label1";

this.label1.Size = new System.Drawing.Size(51, 13);

this.label1.TabIndex = 3;

this.label1.Text = "Count To";

// label2

this.label2.AutoSize = true;

this.label2.Location = new System.Drawing.Point(16, 40);

this.label2.Name = "label2";

this.label2.Size = new System.Drawing.Size(99, 13);

this.label2.TabIndex = 4;

this.label2.Text = "Reach this number";

// btnRemoveDelegate

this.btnRemoveDelegate.Location = new System.Drawing.Point(16, 104);

this.btnRemoveDelegate.Name = "btnRemoveDelegate";

this.btnRemoveDelegate.Size = new System.Drawing.Size(168, 23);

this.btnRemoveDelegate.TabIndex = 5;

this.btnRemoveDelegate.Text = "Remove second handler";

this.btnRemoveDelegate.Click += new System.EventHandler(this.btnRemoveDelegate_Click);

// Form1

this.AutoScaleBaseSize = new System.Drawing.Size(5, 13);

this.ClientSize = new System.Drawing.Size(224, 134);

this.Controls.AddRange(new System.Windows.Forms.Control[]

{

this.btnRemoveDelegate,

this.label2,

this.label1,

this.txtCountTo,

this.txtReachable,

this.cmdRun});

this.Name = "Form1";

this.Text = "Events";

this.ResumeLayout(false);

}

#endregion

/**//// <summary>

/// The main entry point for the application.

/// </summary>

[STAThread]

static void Main()

{

Application.Run(new Form1());

}

private void btnRun_Click(object sender, System.EventArgs e)

{

if(txtCountTo.Text == "" || txtReachable.Text=="")

return;

oCounter.CountTo(Convert.ToInt32(txtCountTo.Text), Convert.ToInt32(txtReachable.Text));

}

private void oCounter_NumberReached(object sender, NumberReachedEventArgs e)

{

MessageBox.Show("Reached: " + e.ReachedNumber.ToString());

}

private void oCounter_NumberReached2(object sender, NumberReachedEventArgs e)

{

MessageBox.Show("Reached2: " + e.ReachedNumber.ToString());

}

private void btnRemoveDelegate_Click(object sender, System.EventArgs e)

{

oCounter.NumberReached -= new NumberReachedEventHandler(oCounter_NumberReached2);

oCounter.CountTo(Convert.ToInt32(txtCountTo.Text), Convert.ToInt32(txtReachable.Text));

}

Counter.cs

using System;

namespace Events

{

public delegate void NumberReachedEventHandler(object sender, NumberReachedEventArgs e);

/**//// <summary>

/// Summary description for Counter.

/// </summary>

public class Counter

{

public event NumberReachedEventHandler NumberReached;

public Counter()

{

// TODO: Add constructor logic here

}

public void CountTo(int countTo, int reachableNum)

{

if(countTo < reachableNum)

throw new ArgumentException("reachableNum should be less than countTo");

for(int ctr=0;ctr<=countTo;ctr++)

{

if(ctr == reachableNum)

{

NumberReachedEventArgs e = new NumberReachedEventArgs(reachableNum);

OnNumberReached(e);

return;//don't count any more

}

protected virtual void OnNumberReached(NumberReachedEventArgs e)

{

if(NumberReached!=null)

{

NumberReached(this, e);

}

public class NumberReachedEventArgs : EventArgs

{

private int _reached;

public NumberReachedEventArgs(int num)

{

this._reached = num;

}

public int ReachedNumber

{

get

{

return _reached;

}

using System;

namespace Events

{

public delegate void NumberReachedEventHandler(object sender, NumberReachedEventArgs e);

/**//// <summary>

/// Summary description for Counter.

/// </summary>

public class Counter

{

public event NumberReachedEventHandler NumberReached;

public Counter()

{

// TODO: Add constructor logic here

}

public void CountTo(int countTo, int reachableNum)

{

if(countTo < reachableNum)

throw new ArgumentException("reachableNum should be less than countTo");

for(int ctr=0;ctr<=countTo;ctr++)

{

if(ctr == reachableNum)

{

NumberReachedEventArgs e = new NumberReachedEventArgs(reachableNum);

OnNumberReached(e);

return;//don't count any more

}

protected virtual void OnNumberReached(NumberReachedEventArgs e)

{

if(NumberReached!=null)

{

NumberReached(this, e);

}

public class NumberReachedEventArgs : EventArgs

{

private int _reached;

public NumberReachedEventArgs(int num)

{

this._reached = num;

}

public int ReachedNumber

{

get

{

return _reached;

}

using System;

namespace Events

{

public delegate void NumberReachedEventHandler(object sender, NumberReachedEventArgs e);

/**//// <summary>

/// Summary description for Counter.

/// </summary>

public class Counter

{

public event NumberReachedEventHandler NumberReached;

public Counter()

{

// TODO: Add constructor logic here

}

public void CountTo(int countTo, int reachableNum)

{

if(countTo < reachableNum)

throw new ArgumentException("reachableNum should be less than countTo");

for(int ctr=0;ctr<=countTo;ctr++)

{

if(ctr == reachableNum)

{

NumberReachedEventArgs e = new NumberReachedEventArgs(reachableNum);

OnNumberReached(e);

return;//don't count any more

}

protected virtual void OnNumberReached(NumberReachedEventArgs e)

{

if(NumberReached!=null)

{

NumberReached(this, e);

}

public class NumberReachedEventArgs : EventArgs

{

private int _reached;

public NumberReachedEventArgs(int num)

{

this._reached = num;

}

public int ReachedNumber

{

get

{

return _reached;

}