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POActivator.CreateInstance: Dynamic Instantiation of Classes
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  1. POActivator.CreateInstance: Dynamic Instantiation of Classes
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    copied!<p>I am designing a loosely-coupled structure. I want to <strong>call classes from different assemblies/namespaces via a code which is represented by a String</strong>. My design is, each of client's business rules is on different assemblies and not dependent on each other (ONE client is to ONE DLL ratio) so that when I made an update on business rules of 1 client, it would not affect the others. My attention now is on using Factory Design and using <strong>Activator.CreateInstance()</strong> Method.</p> <p>This is the project setup (2+n DLL's)</p> <pre><code> namespace Foundation; // where the interfaces/abstract resides namespace Factory; // has dependency on Foundation assembly namespace Client1; // client1's DLL, no dependency namespace Client2; // client2's DLL, no dependency The UI // only referenced to the Foundation and Factory not the Clients </code></pre> <p>The actual code</p> <pre><code> namespace Foundation { public interface IBusinessRules { string GetBusinessRule(); } } namespace Client1 //DLL for client 1 { public class BusinessRules : Foundation.IBusinessRules { public string GetBusinessRule() { return "Client1 Business Rule"; } } } namespace Client2 //DLL for client 2 { public class BusinessRules : Foundation.IBusinessRules { public string GetBusinessRule() { return "Client2 Business Rule"; } } } namespace Factory { public static class Invoker&lt;T&gt; where T: Foundation.IBusinessRules { public static T FetchInstance(string clientCode) { return (T)Activator.CreateInstance(Type.GetType(clientCode)); } } } //sample implementation that generates unhandled Exception using Factory; using Foundation; static void Main(string[] args) { //the parameter is maintained in the database IBusinessRules objClient1 = Invoker&lt;IBusinessRules&gt;.FetchInstance("Client1"); //should call Client1.BusinessRules method Console.WriteLine(objClient.GetBusinessRule()); Console.Read(); objClient = Invoker&lt;IBusinessRules&gt;.FetchInstance("Client2"); //should call Client2.BusinessRules method Console.WriteLine(objClient.GetBusinessRule()); Console.Read(); } </code></pre> <p>Any idea why my sample doesn't work? And any suggestion to improve the design? Thanks in advance.</p> <p><strong>How about using</strong> </p> <blockquote> <p>Expression.Lambda</p> </blockquote> <p>anyone?</p>
 

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