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EventArgs Class

EventArgs is the base class for classes containing event data.

Namespace: System
Assembly: mscorlib (in mscorlib.dll)

[SerializableAttribute] 
[ComVisibleAttribute(true)] 
public class EventArgs
/** @attribute SerializableAttribute() */ 
/** @attribute ComVisibleAttribute(true) */ 
public class EventArgs
SerializableAttribute 
ComVisibleAttribute(true) 
public class EventArgs

This class contains no event data; it is used by events that do not pass state information to an event handler when an event is raised. If the event handler requires state information, the application must derive a class from this class to hold the data.

For example, the System.AssemblyLoadEventArgs class is used to hold the data for assembly load events, and contains a System.Reflection.Assembly that describes the loaded assembly.

For more information about events, see the EventHandler topic.

The following code sample illustrates the use of EventArgs.

In this sample, FireEventArgs is a set of event arguments derived from EventArgs, and passed to the FireEventHandler when an event is raised by calling ActivateFireAlarm.


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 static void 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


Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Windows 98, Windows 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see System Requirements.

.NET Framework

Supported in: 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 2.0, 1.0

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