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Dependency Injection with the Microsoft Unity Container: Injecting multiple ICommand implementations

Injecting multiple ICommand implementations with the Microsoft Unity container

Hello, and welcome to my second article on Dependency Injection and IoC with the Microsoft Unity Framework.  In my last post Dependency Injection and Inversion of Control with the Microsoft Unity Container I discussed the importance of coding to an interface and not a concrete implementation.  I also introduced the idea of dependencies, and dependency injection using Unity.

As I've been working a lot lately in XAML using the MVVM (Model-View-ViewModel) Pattern, I find myself implementing a lot of ICommand classes.  The ICommand interface is very simple, with a method for execution, a method to check if the command can execute, and an event handler to specify the state of the command execution.  The interface is very useful because of the way that XAML can bind to these commands to perform actions on button click's and other user interface actions.  

Dependency Injection with multiple ICommand implementations

So I had a lot of implementations of the ICommand interface that were used to call on the service layer of my application to complete application tasks. My past experience up until this point never required for me to register one type with multiple interfaces.  Luckily, I found it that Unity has a nice way to handle this issue.

So when I setup my container, I register the commands like this

_container.RegisterType<ICommand, LoadQuizesCommand>("LoadQuizes");
_container.RegisterType<ICommand, CreateQuizCommand>("CreateQuiz");

_container.RegisterType<IQuizService, QuizService>();
_container.RegisterType<IMainQuizMenuViewModel, MainQuizMenuViewModel>();

Then here is the ViewModel where the dependencies are injected in the constructor.

using Domain.QuizIt;
using Microsoft.Practices.Unity;
using QuizIt.ViewModels.Interfaces;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows.Input;
using Service.QuizIt.Interfaces;

namespace QuizIt.ViewModels
{
    /// <summary>
    /// This represents the ViewModel that is bound to the Main Quiz user interface.
    /// </summary>
    public class MainQuizMenuViewModel : IMainQuizMenuViewModel
    {

        #region "public properties"

        public ICommand LoadQuizesCommand { get; set; }
        public ICommand CreateQuizCommand { get; set; }
        public IQuizService QuizServiceManager { get; set; }
        public List<Quiz> Quizes { get; set; }
        public string QuizName { get; set; }
        public string QuizDescription { get; set; }

        #endregion

        #region "constructors"

        public MainQuizMenuViewModel([Dependency("LoadQuizes")]ICommand loadQuizesCommand,
            [Dependency("CreateQuiz")]ICommand createQuizCommand, [Dependency]IQuizService quizServiceManager)
        {
            this.LoadQuizesCommand = loadQuizesCommand;
            this.CreateQuizCommand = createQuizCommand;
            this.QuizServiceManager = quizServiceManager;
        }

        #endregion
    }
}

Notice how I specify the same names in the Dependency attributes in the constructors as I did when registering the types.  This way I can specify the command by name and resolve different implementations for multiple ICommand interfaces.

I hope you enjoyed reading this post.  Please feel free to comment if you have any tricks of your own with injecting multiple interfaces.

 

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About the author

My name is Buddy James.  I'm a Microsoft Certified Solutions Developer from the Nashville, TN area.  I'm a Software Engineer, an author, a blogger (http://www.refactorthis.net), a mentor, a thought leader, a technologist, a data scientist, and a husband.  I enjoy working with design patterns, data mining, c#, WPF, Silverlight, WinRT, XAML, ASP.NET, python, CouchDB, RavenDB, Hadoop, Android(MonoDroid), iOS (MonoTouch), and Machine Learning. I love technology and I love to develop software, collect data, analyze the data, and learn from the data.  When I'm not coding,  I'm determined to make a difference in the world by using data and machine learning techniques. (follow me at @budbjames).  

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