EventArgs クラスとは何？わかりやすく解説 Weblio辞書

.NET Framework クラスライブラリリファレンス

索引トップ用語の索引ランキング

EventArgs クラス

EventArgs は、イベントデータが格納されているクラスの基本クラスです。

名前空間: System
アセンブリ: mscorlib (mscorlib.dll 内)
構文

Visual Basic (宣言)

<SerializableAttribute> _
<ComVisibleAttribute(True)> _
Public Class EventArgs

Visual Basic (使用法)

Dim instance As EventArgs

[SerializableAttribute] 
[ComVisibleAttribute(true)] 
public class EventArgs

C++

[SerializableAttribute] 
[ComVisibleAttribute(true)] 
public ref class EventArgs

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

JScript

SerializableAttribute 
ComVisibleAttribute(true) 
public class EventArgs

解説

このクラスにはイベントデータは格納されません。このクラスは、イベントの発生時にステータス情報をイベントハンドラに渡さないイベントによって使用されます。イベントハンドラがステータス情報を必要とする場合、アプリケーションは、そのデータを保持するために、このクラスからクラスを派生させる必要があります。

たとえば、System.AssemblyLoadEventArgs クラスは、アセンブリ読み込みイベントのデータを保持するために使用され、読み込まれたアセンブリを記述する System.Reflection.Assembly を格納します。

イベントの詳細については、EventHandler のトピックを参照してください。

使用例

EventArgs の使用方法については、次のコード例を参照してください。

この例では、FireEventArgs が EventArgs から派生したイベント引数の集合になっています。ActivateFireAlarm を呼び出してイベントが発生すると、FireEventHandler に渡されます。

Visual Basic

Imports System

 _

' FireEventArgs: a custom event inherited from EventArgs.

Public Class FireEventArgs
   Inherits EventArgs
   
   Public Sub New(room As
 String, ferocity As Integer)
      Me.room = room
      Me.ferocity = ferocity
   End Sub 'New
   
   ' The fire event will have two pieces of information-- 
   ' 1) Where the fire is, and 2) how "ferocious" it is. 
 
   Public room As String
   Public ferocity As Integer
End Class 'FireEventArgs
 _ 
'end of class FireEventArgs

Public Class FireAlarm
   
   ' Events are handled with delegates, so we must establish a FireEventHandler
   ' as a delegate:

   Delegate Sub FireEventHandler(sender As
 Object, fe As FireEventArgs)
   
   ' Now, create a public event "FireEvent" whose type is
 our FireEventHandler delegate.

   Public Event FireEvent As
 FireEventHandler
   
   
   ' This will be the starting point of our event-- it will create FireEventArgs
,
   ' and then raise the event, passing FireEventArgs.

   Public Sub ActivateFireAlarm(room As
 String, ferocity As Integer)
      
      Dim fireArgs As New
 FireEventArgs(room, ferocity)
      
      '  Now, raise the event by invoking the delegate. Pass in 
      '  the object that initated the event (Me) as well as FireEventArgs.
 
      '  The call must match the signature of FireEventHandler.

      RaiseEvent FireEvent(Me, fireArgs)

   End Sub 'ActivateFireAlarm
End Class 'FireAlarm

' The following event will be the EventHandler.
 
Class FireHandlerClass
   
   
   ' Create a FireAlarm to handle and raise the fire events. 

   Public Sub New(fireAlarm
 As FireAlarm)
      
      ' Add a delegate containing the ExtinguishFire function to the
 class'
      ' event so that when FireAlarm is raised, it will subsequently
 execute 
      ' ExtinguishFire.

      AddHandler fireAlarm.FireEvent, AddressOf
 ExtinguishFire

   End Sub 'New
   
   
   ' This is the function to be executed when a fire event is raised.
   
   Sub ExtinguishFire(sender As Object,
 fe As FireEventArgs)
     
      Console.WriteLine() 
      Console.WriteLine("The ExtinguishFire function was called
 by {0}.", sender.ToString())
      
      ' Now, act in response to the event.

      If fe.ferocity < 2 Then
         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 Then
            Console.WriteLine("Using Fire Extinguisher 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 If
      End If 'end of class FireHandlerClass
   End Sub 'ExtinguishFire
End Class 'FireHandlerClass

Public Class FireEventTest
   
   Public Shared Sub Main()
      
      ' Create an instance of the class that will be raising the event.
      Dim myFireAlarm As 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.
 

     Dim myFireHandler As New
 FireHandlerClass(myFireAlarm)
        
      ' Now, use the FireAlarm class to raise a few events. 

      myFireAlarm.ActivateFireAlarm("Kitchen", 3)
      myFireAlarm.ActivateFireAlarm("Study", 1)
      myFireAlarm.ActivateFireAlarm("Porch", 5)
      
      Return
   End Sub 'Main 'end of main
End Class 'FireEventTest ' end
 of FireEventTest

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

C++

using namespace System;

// FireEventArgs: a custom event inherited from EventArgs.
public ref class FireEventArgs: public
 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.
  
   String^ room;
   int ferocity;
};


//end of class FireEventArgs
// Class with a function that creates the eventargs and initiates the
 event
public ref class FireAlarm
{
public:
   delegate void FireEventHandler(    // Events are
 handled with delegates, so we must establish a FireEventHandler
   // as a delegate:
   Object^ sender, FireEventArgs^ fe );
   event FireEventHandler^ FireEvent;

   // Now, create a public event "FireEvent" whose type is
 our FireEventHandler delegate. 
   // This will be the starting point of our event-- it will create
 FireEventArgs,
   // and then raise the event, passing FireEventArgs. 
   void ActivateFireAlarm( String^ room, int
 ferocity )
   {
      FireEventArgs^ fireArgs = gcnew 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
ref class FireHandlerClass
{
public:

   // Create a FireAlarm to handle and raise the fire events. 
   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 += gcnew FireAlarm::FireEventHandler( this,
 &FireHandlerClass::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 );
      
      // 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
int main()
{
   
   // Create an instance of the class that will be firing an event.
   FireAlarm^ myFireAlarm = gcnew 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 = gcnew 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 );
} //end of main