Вызов и прием событий

Следующий пример программы демонстрирует инициализацию события в одном классе и обработку этого события в другом классе. Класс AlarmClock определяет открытое событие Alarm и предоставляет методы для инициализации события. Класс AlarmEventArgs является производным от EventArgs и определяет данные, относящиеся к событию Alarm. Класс WakeMeUp определяет метод AlarmRang, который обрабатывает событие Alarm. Класс AlarmDriver использует классы вместе, устанавливая метод AlarmRang класса WakeMeUp для обработки события Alarm класса AlarmClock.

Пример

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// The SnoozePressed property indicates whether the snooze

// button is pressed on the alarm when the alarm event is generated.

//

public bool SnoozePressed

{

get {return snoozePressed;}

}

// The AlarmText property that contains the wake-up message.

//

public string AlarmText

{

get

{

if (snoozePressed)

{

return ("Wake Up!!! Snooze time is over.");

}

else

{

return ("Wake Up!");

}

}

}

}

// Delegate declaration.

//

public delegate void AlarmEventHandler(object sender, AlarmEventArgs e);

// The Alarm class that raises the alarm event.

//

public class AlarmClock

{

private bool snoozePressed = false;

private int nrings = 0;

private bool stop = false;

// The Stop property indicates whether the

// alarm should be turned off.

//

public bool Stop

{

get {return stop;}

set {stop = value;}

}

--------------

// The SnoozePressed property indicates whether the snooze

// button is pressed on the alarm when the alarm event is generated.

//

public bool SnoozePressed

{

get {return snoozePressed;}

set {snoozePressed = value;}

}

// The event member that is of type AlarmEventHandler.

//

public event AlarmEventHandler Alarm;

// The protected OnAlarm method raises the event by invoking

// the delegates. The sender is always this, the current instance

// of the class.

//

protected virtual void OnAlarm(AlarmEventArgs e)

{

AlarmEventHandler handler = Alarm;

if (handler != null)

{

// Invokes the delegates.

handler(this, e);

}

}

-------------

// This alarm clock does not have

// a user interface.

// To simulate the alarm mechanism it has a loop

// that raises the alarm event at every iteration

// with a time delay of 300 milliseconds,

// if snooze is not pressed. If snooze is pressed,

// the time delay is 1000 milliseconds.

//

public void Start()

{

for (;;)

{

nrings++;

if (stop)

{

break;

}

else if (snoozePressed)

{

System.Threading.Thread.Sleep(1000);

{

AlarmEventArgs e = new AlarmEventArgs(snoozePressed,

nrings);

OnAlarm(e);

}

}

else

{

System.Threading.Thread.Sleep(300);

AlarmEventArgs e = new AlarmEventArgs(snoozePressed,

nrings);

OnAlarm(e);

}

}

}

}

----------------

// The WakeMeUp class has a method AlarmRang that handles the

// alarm event.

//

public class WakeMeUp

{

public void AlarmRang(object sender, AlarmEventArgs e)

{

Console.WriteLine(e.AlarmText +"\n");

if (!(e.SnoozePressed))

{

if (e.NumRings % 10 == 0)

{

Console.WriteLine(" Let alarm ring? Enter Y");

Console.WriteLine(" Press Snooze? Enter N");

Console.WriteLine(" Stop Alarm? Enter Q");

String input = Console.ReadLine();

if (input.Equals("Y") ||input.Equals("y")) return;

else if (input.Equals("N") || input.Equals("n"))

{

((AlarmClock)sender).SnoozePressed = true;

return;

}

else

{

((AlarmClock)sender).Stop = true;

return;

}

}

}

else

{

Console.WriteLine(" Let alarm ring? Enter Y");

Console.WriteLine(" Stop Alarm? Enter Q");

String input = Console.ReadLine();

if (input.Equals("Y") || input.Equals("y")) return;

else

{

((AlarmClock)sender).Stop = true;

return;

}

}

}

}

----------------

// The driver class that hooks up the event handling method of

// WakeMeUp to the alarm event of an Alarm object using a delegate.

// In a forms-based application, the driver class is the

// form.

//

public class AlarmDriver

{

public static void Main (string[] args)

{

// Instantiates the event receiver.

WakeMeUp w= new WakeMeUp();

// Instantiates the event source.

AlarmClock clock = new AlarmClock();

// Wires the AlarmRang method to the Alarm event.

clock.Alarm += new AlarmEventHandler(w.AlarmRang);

clock.Start();

}

}

}

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How to: Implement Interface Events

An interface can declare an event. The following example shows how to implement interface events in a class. Basically the rules are the same as when you implement any interface method or property.

To implement interface events in a class

• Declare the event in your class and then invoke it in the appropriate areas.