Lesson 49 - Use a Dictionary to Store Event Instances

One use for accessor-declarations is to expose a large number of events without allocating a field for each event, but instead using a Dictionary to store the event instances. This is only useful if you have a very large number of events, but you expect most of the events will not be implemented.

public delegate void EventHandler1(int i);
public delegate void EventHandler2(string s);

public class PropertyEventsSample
{
private System.Collections.Generic.Dictionary eventTable;

public PropertyEventsSample()
{
eventTable = new System.Collections.Generic.Dictionary();
eventTable.Add("Event1", null);
eventTable.Add("Event2", null);
}

public event EventHandler1 Event1
{
add
{
lock (eventTable)
{
eventTable["Event1"] = (EventHandler1)eventTable["Event1"] + value;
}
}
remove
{
lock (eventTable)
{
eventTable["Event1"] = (EventHandler1)eventTable["Event1"] - value;
}
}
}

public event EventHandler2 Event2
{
add
{
lock (eventTable)
{
eventTable["Event2"] = (EventHandler2)eventTable["Event2"] + value;
}
}
remove
{
lock (eventTable)
{
eventTable["Event2"] = (EventHandler2)eventTable["Event2"] - value;
}
}
}

internal void RaiseEvent1(int i)
{
EventHandler1 handler1;
if (null != (handler1 = (EventHandler1)eventTable["Event1"]))
{
handler1(i);
}
}

internal void RaiseEvent2(string s)
{
EventHandler2 handler2;
if (null != (handler2 = (EventHandler2)eventTable["Event2"]))
{
handler2(s);
}
}
}

public class TestClass
{
public static void Delegate1Method(int i)
{
System.Console.WriteLine(i);
}

public static void Delegate2Method(string s)
{
System.Console.WriteLine(s);
}

static void Main()
{
PropertyEventsSample p = new PropertyEventsSample();

p.Event1 += new EventHandler1(TestClass.Delegate1Method);
p.Event1 += new EventHandler1(TestClass.Delegate1Method);
p.Event1 -= new EventHandler1(TestClass.Delegate1Method);
p.RaiseEvent1(2);

p.Event2 += new EventHandler2(TestClass.Delegate2Method);
p.Event2 += new EventHandler2(TestClass.Delegate2Method);
p.Event2 -= new EventHandler2(TestClass.Delegate2Method);
p.RaiseEvent2("TestString");

Console.ReadLine();
}
}