To subscribe to events programmatically

1. Define an event handler method whose signature matches the delegate signature for the event. For example, if the event is based on the EventHandler delegate type, the following code represents the method stub:

void HandleCustomEvent(object sender, EventArgs a) { // Do something useful here. }

2. Use the addition assignment operator (+=) to attach your event handler to the event. In the following example, assume that an object named publisher has an event named RaiseCustomEvent. Note that the subscriber class needs a reference to the publisher class in order to subscribe to its events.

publisher.RaiseCustomEvent += HandleCustomEvent;

3. Note that the previous syntax is new in C# 2.0. It is exactly equivalent to the C# 1.0 syntax in which the encapsulating delegate must be explicitly created by using the new keyword:

publisher.RaiseCustomEvent += new CustomEventHandler(HandleCustomEvent);

4. An event handler can also be added by using a lambda expression:

public Form1() { InitializeComponent(); // Use a lambda expression to define an event handler. this.Click += (s,e) => { MessageBox.Show( ((MouseEventArgs)e).Location.ToString());}; }

 

Подписка на события программными средствами

1. Определите метод обработчика событий, подпись которого соответствует подписи делегата для события. Например, если событие основано на типе делегата EventHandler, то следующий код представляет заглушку метода:

void HandleCustomEvent(object sender, CustomEventArgs a) { // Do something useful here. }

2. Чтобы присоединить обработчик событий к событию, используйте оператор назначения сложения (+=). В следующем примере предположим, что объект с именем publisher имеет событие с именем RaiseCustomEvent. Обратите внимание, что для класса подписчика требуется ссылка на класс издателя, чтобы подписаться на его события.

publisher.RaiseCustomEvent += HandleCustomEvent;

3. Обратите внимание, что предыдущий синтаксис является нововведением в языке C# версии 2.0. Он в точности соответствует синтаксису C# 1.0, в котором при помощи ключевого слова new должен быть явно создан инкапсулирующий делегат.

publisher.RaiseCustomEvent += new CustomEventHandler(HandleCustomEvent);

4. Для добавления обработчика событий можно также использовать лямбда-выражение.

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Дополнительные сведения см. в разделе Использование лямбда-выражений вне LINQ.

To subscribe to events by using an anonymous method

· Use the addition assignment operator (+=) to attach your anonymous method to the event. In the following example, assume that an object named publisher has an event named RaiseCustomEvent and that a CustomEventArgs class has also been defined to carry some kind of specialized event information. Note that the subscriber class needs a reference to publisher in order to subscribe to its events.

publisher.RaiseCustomEvent += delegate(object o, CustomEventArgs e) { string s = o.ToString() + " " + e.ToString(); Console.WriteLine(s); };

· It is important to notice that you cannot easily unsubscribe from an event if you used an anonymous method to subscribe to it. To unsubscribe in this scenario, go back to the code where you subscribe to the event, store the anonymous method in a delegate variable, and then add the delegate to the event.

Unsubscribing

To prevent your event handler from being invoked when the event is raised, unsubscribe from the event. In order to prevent resource leaks, you should unsubscribe from events before you dispose of a subscriber object. Until you unsubscribe from an event, the multicast delegate that underlies the event in the publishing object has a reference to the delegate that encapsulates the subscriber's event handler. As long as the publishing object holds that reference, garbage collection will not delete your subscriber object.