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copied!<p>Since I wrote the MSDN article you are referring to, I guess I have to answer this one.</p> <p>First, I anticipated this question and that's why I wrote a blog post that shows a more or less real use case for ExpandoObject: <a href="http://blogs.msdn.com/csharpfaq/archive/2009/10/01/dynamic-in-c-4-0-introducing-the-expandoobject.aspx" rel="noreferrer">Dynamic in C# 4.0: Introducing the ExpandoObject</a>. </p> <p>Shortly, ExpandoObject can help you create complex hierarchical objects. For example, imagine that you have a dictionary within a dictionary:</p> <pre><code>Dictionary<String, object> dict = new Dictionary<string, object>(); Dictionary<String, object> address = new Dictionary<string,object>(); dict["Address"] = address; address["State"] = "WA"; Console.WriteLine(((Dictionary<string,object>)dict["Address"])["State"]); </code></pre> <p>The deeper is the hierarchy, the uglier is the code. With ExpandoObject it stays elegant and readable.</p> <pre><code>dynamic expando = new ExpandoObject(); expando.Address = new ExpandoObject(); expando.Address.State = "WA"; Console.WriteLine(expando.Address.State); </code></pre> <p>Second, as it was already pointed out, ExpandoObject implements INotifyPropertyChanged interface which gives you more control over properties than a dictionary.</p> <p>Finally, you can add events to ExpandoObject like here:</p> <pre><code>class Program { static void Main(string[] args) { dynamic d = new ExpandoObject(); // Initialize the event to null (meaning no handlers) d.MyEvent = null; // Add some handlers d.MyEvent += new EventHandler(OnMyEvent); d.MyEvent += new EventHandler(OnMyEvent2); // Fire the event EventHandler e = d.MyEvent; if (e != null) { e(d, new EventArgs()); } // We could also fire it with... // d.MyEvent(d, new EventArgs()); // ...if we knew for sure that the event is non-null. } static void OnMyEvent(object sender, EventArgs e) { Console.WriteLine("OnMyEvent fired by: {0}", sender); } static void OnMyEvent2(object sender, EventArgs e) { Console.WriteLine("OnMyEvent2 fired by: {0}", sender); } } </code></pre>

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