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POPassing parameters to constructors using Autofac
 

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  1. POPassing parameters to constructors using Autofac
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    <p>I'm very new to autofac so it's possible that I'm completely misusing it.</p> <p>Let's say I have a class that has this structure:</p> <pre><code>public class HelperClass : IHelperClass { public HelperClass(string a, string b) { this.A = a; this.B = b; } } </code></pre> <p>and I have two classes that use that class, but require different defaults for the constructor. The second constructor is JUST for testing purposes -- we will always want a HelperClass in the "real" app.:</p> <pre><code>public class DoesSomething: IDoesSomething { public DoesSomething() : this(new HelperClass("do", "something")); { } internal DoesSomething(IHelperClass helper) { this.Helper = helper; } } public class DoesSomethingElse : IDoesSomethingElse { public DoesSomethingElse() : this(new HelperClass("does", "somethingelse")); { } internal DoesSomethingElse(IHelperClass helper) { this.Helper = helper; } } </code></pre> <p>Here's my AutoFac module:</p> <pre><code>public class SomethingModule: Module { protected override void Load(ContainerBuilder builder) { builder.RegisterType&lt;DoesSomething&gt;().As&lt;IDoesSomething&gt;(); builder.RegisterType&lt;DoesSomethingElse&gt;().As&lt;IDoesSomethingElse(); } } </code></pre> <p>My question(s):</p> <ol> <li>When I call resolve on DoesSomething or DoesSomethignElse -- will it resolve the internal constructor instead of the public one? Do I need to leave IHelperClass unregistered?</li> <li>If yes, how do I make it pass different parameters to each instance of IHelperClass depending on whether it's used in DoesSomething or DoesSomethingElse?</li> </ol>
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    1. COIt's very strange to have such a half-loosely-coupled design. It makes things more difficult. Your public interfaces basically claim that your classes have no dependencies, but in fact they seem to depend on `IHelper`. If so, you'd better make the dependencies visible. Why don't you just remove your parameterless constructor, make the other one public and have your module configuration provide required parameters. You can use `WithParameter` as Daniel Hilgarth has suggested.
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      1. POPassing parameters to constructors using Autofac
      1. USPavel Gatilov
    2. CO@PavelGatilov Thanks, that makes sense. My thinking was that each class "knows" what parameters it needs to pass to the the helper, so it wouldn't make sense passing it in from the outside in the module configuration.
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    3. COIf a class knows what parameters it needs, it couples it to the parameters and breaks the whole idea of Inversion of Control. You should on the contrary design your classes agnostic to their parameters implementations. It's configuration that should know which specific classes to compose together.
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