public static void Main(string[] args)
{
Console.WriteLine("Listing 1-87");
Pub p = new Pub();
p.OnChange += (sender, e) => Console.WriteLine("Subscriber 1 called");
p.OnChange += (sender, e) =>
{
throw new Exception("Error");
};
p.OnChange += (sender, e) => Console.WriteLine("Subscriber 3 called");
try
{
p.Raise();
}
catch (AggregateException ex)
{
Console.WriteLine(ex.InnerExceptions.Count);
}
Console.ReadLine();
}
public static void Main(string[] args)
{
Console.WriteLine("Listing 1-84");
var p = new Pub();
p.OnChange += (sender, e) => Console.WriteLine("Event raised by {0}, with value: {1}", sender, e.Value);
p.Raise();
Console.WriteLine("Listing 1-85");
var pca = new PubWithCustomEventAccessor();
pca.OnChange += (sender, e) => Console.WriteLine("Handler added with custom accessor. Event raised with value: {0}", e.Value);
pca.Raise();
Console.ReadLine();
}
public static void Main(string[] args)
{
Console.WriteLine("Listing 1-82");
// Your code creates a new instance of Pub, subscribes to the event with two different methods and then raises the event by calling p.Raise.
// The Pub class is completely unaware of any subscribers. It just raises the event.
var p = new Pub();
p.OnChange += () => Console.WriteLine("Event raised to method 1");
p.OnChange += () => Console.WriteLine("Event raised to method 2");
p.Raise();
// Although this system works, there are a couple of weaknesses.
// If you change the subscribe line for method 2 to the following,
// you would effectively remove the first subscriber by using = instead of +=:
p.OnChange = () => Console.WriteLine("Overwrite of onchange subscriptions");
p.Raise();
// Another weakness is that nothing prevents outside users of the class from raising the event.
// By just calling p.OnChange() every user of the class can raise the event to all subscribers.
Console.WriteLine("Raising the event from outside");
p.OnChange();
Console.WriteLine();
Console.WriteLine("Listing 1-83");
// To overcome these weaknesses, the C# language uses the special event keyword.
p.OnChangeEvent += () => Console.WriteLine("This from an event keyword event");
// p.OnChangeEvent(); will result in compilation error
p.RaiseEvent();
Console.ReadLine();
}
public static void Main(string[] args)
{
Console.WriteLine("Listing 1-86");
Pub p = new Pub();
p.OnChange += (sender, e) => Console.WriteLine("Subscriber 1 called");
p.OnChange += (sender, e) =>
{
throw new Exception("Error");
};
p.OnChange += (sender, e) => Console.WriteLine("Subscriber 3 called");
p.Raise();
// As you can see, the first subscriber is executed successfully,
// the second one throws an exception,
// and the third one is never called.
Console.ReadLine();
}