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copied!<p>Here's a common example. You need to log in your application. But, at design time, you're not sure if the client wants to log to a database, files, or the event log.</p> <p>So, you want to use DI to defer that choice to one that can be configured by the client.</p> <p>This is some pseudocode (roughly based on Unity):</p> <p>You create a logging interface:</p> <pre><code>public interface ILog { void Log(string text); } </code></pre> <p>then use this interface in your classes</p> <pre><code>public class SomeClass { [Dependency] public ILog Log {get;set;} } </code></pre> <p>inject those dependencies at runtime</p> <pre><code>public class SomeClassFactory { public SomeClass Create() { var result = new SomeClass(); DependencyInjector.Inject(result); return result; } } </code></pre> <p>and the instance is configured in app.config:</p> <pre><code><?xml version="1.0" encoding="utf-8"?> <configuration> <configSections> <section name ="unity" type="Microsoft.Practices.Unity.Configuration.UnityConfigurationSection, Microsoft.Practices.Unity.Configuration"/> </configSections> <unity> <typeAliases> <typeAlias alias="singleton" type="Microsoft.Practices.Unity.ContainerControlledLifetimeManager,Microsoft.Practices.Unity" /> </typeAliases> <containers> <container> <types> <type type="MyAssembly.ILog,MyAssembly" mapTo="MyImplementations.SqlLog, MyImplementations"> <lifetime type="singleton"/> </type> </types> </container> </containers> </unity> </configuration> </code></pre> <p>Now if you want to change the type of logger, you just go into the configuration and specify another type.</p>

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