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POIoC and dynamic objects
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  1. POIoC and dynamic objects
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    copied!<p>I'm having trouble figuring out how to resolve objects that depend on objects that are non deterministically created at runtime. What is the best approach?</p> <p>Imagine something like a word processor. For each document you open, you probably want to create a large number of objects that depend on the document object. </p> <p>As an example, you want to get a hold of an instance of a DocumentEditor:</p> <pre><code>public class DocumentEditor { public DocumentEditor(IDocument document, ISpellChecker spellChecker, IWordCounter wordCounter) { ... } } </code></pre> <p>So far, I have considered two approaches but neither seems like a good fit:</p> <h3>Using factories that get injected</h3> <p>The problem with this approach is that you can end up with a factory for each type you need to create. I.e.</p> <pre><code>public interface ISpellCheckerFactory { ISpellChecker Create(IDocument document); } public interface IWordCounterFactory { IWordCounter Create(IDocument document); } public class DocumentEditorFactory { public DocumentEditorFactory(ISpellCheckerFactory spellCheckerFactory, IWordCounterFactory wordCounterFactory) { ... } public DocumentEditor Create(IDocument document) { ... } } </code></pre> <p>Add another 50 classes and you see the problem...</p> <h3>Using nested containers</h3> <p>Using nested containers removes the need to create a zillion factories. It is actually pretty compact (example using Unity):</p> <pre><code>var child = container.CreateChildContainer(); child.RegisterInstance&lt;IDocument&gt;(theDocument); child.Resolve&lt;DocumentEditor&gt;(); </code></pre> <p>The drawback of this approach is that the container leaks all over the place.</p> <p>(As a side note, implementing in unity this is a bit tricky. See for instance: <a href="https://stackoverflow.com/questions/530405/unity-how-to-register-types-in-the-main-container-but-resolve-in-a-child-conta">How to register types in the main container, but resolve in a child container?</a>)</p> <h3>Hybrid approach</h3> <p>It should be possible to combine the two by implementing a DocumentEditorFactory that creates nested containers and uses the child container to resolve dependencies.</p> <p>Analysis paralysis at its best...</p>
 

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