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c#dependency-injectionasp.net-mvc-5
Raza Jamil
Raza Jamil

Reputation: 274

Setting up dependency injection for my own classes

I have a little problem I can't wrap my head around in relation to Dependency Injections. I learned how to inject dependency for .net mvc 5 controllers using Ninject. However, I can't figure out how to inject dependencies for my own classes.

For example I have a Resource class.

public class Resource
{
       public IResourceLoader ResourceLoader {get;set}

       public Resource(IResourceLoader ResourceLoader)
       {
              this.ResourceLoader = ResourceLoader; 
       }
}

Where IResourceLoader can be implemented to load different types of resources such as XMLLoader. So is it possible to use Ninject to automatically send an instance of XMLLoader when I do 

Resource xmlResource = new Resource(/*do something here/*);

Or better yet if I have a Banner class that inherits from Resource that sets a string resourceType to "xml" and have Ninject filter instances based on that string.

Do I have to implement a factory pattern and do it myself.

Thanks

Upvotes: 0

Views: 157

Answers (2)

Steen Tøttrup
Steen Tøttrup

Reputation: 3835

If you're using Ninject, and in a web project, you should have a NinjectWebCommon.cs class in the App_Start folder?

In the RegisterServicesmethod you could add:

kernel
    .Bind<IResourceLoader>()
    .ToMethod<IResourceLoader>(InstantiateResourceLoader)

And then in the same class, implement the method like so:

private static IResourceLoader InstantiateResourceLoader(IContext ctx) {
    // Put in whatever logic you need to decide on which loader you want to return
    // Use ctx.Kernel.Get<WhatEver>() if you need something from the DI
    return new XMLLoader();
}

Upvotes: 1

gregmac
gregmac

Reputation: 25251

The simple use of DI is where you first register your dependencies (Ninject calls this 'type bindings'):

Bind<IResourceLoader>().To<XMLLoader>();

You can then get an instance of Resource by doing:

IKernel kernel = new StandardKernel();
var resource = kernel.Get<Resource>();

and Ninject will wire-up the constructor types it knows about.

Alternatively, there are several other ways to create dependencies, including, for example the ability to completely control parameters used to create the resource instance:

Bind<IResourceLoader>().ToMethod(context => new XMLResourceLoader("schema.xsd"));

Contextual binding

Ninject also supports something it calls Contextual Binding, where basically you can do something like this:

Bind<IResourceLoader>().To<SimpleResourceLoader>();
Bind<IResourceLoader>().To<XMLResourceLoader>().Named("XML");

public class Banner : Resource
{
   public Banner([Named("XML")] IResourceLoader resourceLoader) 
     : base(resourceLoader) { }
}

Upvotes: 1

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