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Delegado EventHandler<TEventArgs>

 
clsCompliantAlternativeT:System.EventHandler

Representa o método que manipulará um evento quando o evento fornecer dados.

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

[SerializableAttribute]
public delegate void EventHandler<TEventArgs>(
	object sender,
	TEventArgs e
)

Parâmetros

sender
Type: System.Object

A fonte do evento.

e
Type: TEventArgs

Um objeto que contém os dados do evento.

Parâmetros de Tipo

TEventArgs

O tipo dos dados de eventos gerados pelo evento.

The event model in the .NET Framework is based on having an event delegate that connects an event with its handler. To raise an event, two elements are needed:

  • A delegate that refers to a method that provides the response to the event.

  • Optionally, a class that holds the event data, if the event provides data.

The delegate is a type that defines a signature, that is, the return value type and parameter list types for a method. You can use the delegate type to declare a variable that can refer to any method with the same signature as the delegate.

The standard signature of an event handler delegate defines a method that does not return a value. This method's first parameter is of type T:System.Object and refers to the instance that raises the event. Its second parameter is derived from type T:System.EventArgs and holds the event data. If the event does not generate event data, the second parameter is simply the value of the F:System.EventArgs.Empty field. Otherwise, the second parameter is a type derived from T:System.EventArgs and supplies any fields or properties needed to hold the event data.

The T:System.EventHandler`1 delegate is a predefined delegate that represents an event handler method for an event that generates data. The advantage of using T:System.EventHandler`1 is that you do not need to code your own custom delegate if your event generates event data. You simply provide the type of the event data object as the generic parameter.

To associate the event with the method that will handle the event, add an instance of the delegate to the event. The event handler is called whenever the event occurs, unless you remove the delegate.

For more information about event handler delegates, see Handling and Raising Events.

The following example shows an event named ThresholdReached. The event is associated with an T:System.EventHandler`1 delegate.

using System;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            Counter c = new Counter(new Random().Next(10));
            c.ThresholdReached += c_ThresholdReached;

            Console.WriteLine("press 'a' key to increase total");
            while (Console.ReadKey(true).KeyChar == 'a')
            {
                Console.WriteLine("adding one");
                c.Add(1);
            }
        }

        static void c_ThresholdReached(object sender, ThresholdReachedEventArgs e)
        {
            Console.WriteLine("The threshold of {0} was reached at {1}.", e.Threshold,  e.TimeReached);
            Environment.Exit(0);
        }
    }

    class Counter
    {
        private int threshold;
        private int total;

        public Counter(int passedThreshold)
        {
            threshold = passedThreshold;
        }

        public void Add(int x)
        {
            total += x;
            if (total >= threshold)
            {
                ThresholdReachedEventArgs args = new ThresholdReachedEventArgs();
                args.Threshold = threshold;
                args.TimeReached = DateTime.Now;
                OnThresholdReached(args);
            }
        }

        protected virtual void OnThresholdReached(ThresholdReachedEventArgs e)
        {
            EventHandler<ThresholdReachedEventArgs> handler = ThresholdReached;
            if (handler != null)
            {
                handler(this, e);
            }
        }

        public event EventHandler<ThresholdReachedEventArgs> ThresholdReached;
    }

    public class ThresholdReachedEventArgs : EventArgs
    {
        public int Threshold { get; set; }
        public DateTime TimeReached { get; set; }
    }
}

Plataforma Universal do Windows
Disponível desde 8
.NET Framework
Disponível desde 2.0
Biblioteca de Classes Portátil
Com suporte no: plataformas portáteis do .NET
Silverlight
Disponível desde 2.0
Windows Phone Silverlight
Disponível desde 7.0
Windows Phone
Disponível desde 8.1
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