Essential Books

Event Properties

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If a class raises a large the number of events, the storage cost of one field per delegate may not be acceptable. The .NET Framework provides event properties for these cases. This way you can use another data structure like EventHandlerList to store event delegates: 

public class SampleClass 
{
    // Define the delegate collection.
    protected EventHandlerList eventDelegates = new EventHandlerList();

    // Define a unique key for each event.
    static readonly object someEventKey = new object();

    // Define the SomeEvent event property.
    public event EventHandler SomeEvent
    {
        add
        {
            // Add the input delegate to the collection.
            eventDelegates.AddHandler(someEventKey, value);
        }
        remove
        {
            // Remove the input delegate from the collection.
            eventDelegates.RemoveHandler(someEventKey, value);
        }
    }

    // Raise the event with the delegate specified by someEventKey
    protected void OnSomeEvent(EventArgs e)
    {
        var handler = (EventHandler)eventDelegates[someEventKey];
        if (handler != null)
            handler(this, e);
    }
}

This approach is widely used in GUI frameworks like WinForms where controls can have dozens and even hundreds of events.

Note that EventHandlerList is not thread-safe, so if you expect your class to be used from multiple threads, you will need to add lock statements or other synchronization mechanism (or use a storage that provides thread safety).

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Events:
* Events
* Declaring and Raising Events
* Creating cancelable event
* Event Properties
* Standard Event Declaration
* Anonymous Event Handler Declaration
* Non-Standard Event Declaration
* Creating custom EventArgs containing additional data
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0 Getting Started With C#
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116 Lock Statement
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118 Task Parallel Library TPL Dataflow Constructs
119 Functional Programming
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125 Accessing Databases
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151 Creating Own MessageBox in Windows Form Application
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154 Windows Communication Foundation
155 Contributors