Can someone explain Microsoft Unity

Question

I ve been reading the articles on MSDN about Unity  Dependency Injection  Inversion of Control   but I think I need it explained in simple terms  or simple examples   I m familiar with the MVPC pattern  we use it here   but I just can t really grasp this Unity thing yet  and I think it s the next step in our application design

User · Answer

I am covering most of the examples of Dependency Injection in ASP.NET Web API 2

public interface IShape
{
    string Name { get; set; }
}

public class NoShape : IShape
{
    public string Name { get; set; } = "I have No Shape";
}

public class Circle : IShape
{
    public string Name { get; set; } = "Circle";
}

public class Rectangle : IShape
{
    public Rectangle(string name)
    {
        this.Name = name;
    }

    public string Name { get; set; } = "Rectangle";
}

In DIAutoV2Controller.cs Auto Injection mechanism is used

[RoutePrefix("api/v2/DIAutoExample")]
public class DIAutoV2Controller : ApiController
{
    private string ConstructorInjected;
    private string MethodInjected1;
    private string MethodInjected2;
    private string MethodInjected3;

    [Dependency]
    public IShape NoShape { get; set; }

    [Dependency("Circle")]
    public IShape ShapeCircle { get; set; }

    [Dependency("Rectangle")]
    public IShape ShapeRectangle { get; set; }

    [Dependency("PiValueExample1")]
    public double PiValue { get; set; }

    [InjectionConstructor]
    public DIAutoV2Controller([Dependency("Circle")]IShape shape1, [Dependency("Rectangle")]IShape shape2, IShape shape3)
    {
        this.ConstructorInjected = shape1.Name + " & " + shape2.Name + " & " + shape3.Name;
    }

    [NonAction]
    [InjectionMethod]
    public void Initialize()
    {
        this.MethodInjected1 = "Default Initialize done";
    }

    [NonAction]
    [InjectionMethod]
    public void Initialize2([Dependency("Circle")]IShape shape1)
    {
        this.MethodInjected2 = shape1.Name;
    }

    [NonAction]
    [InjectionMethod]
    public void Initialize3(IShape shape1)
    {
        this.MethodInjected3 = shape1.Name;
    }

    [HttpGet]
    [Route("constructorinjection")]
    public string constructorinjection()
    {
        return "Constructor Injected: " + this.ConstructorInjected;
    }

    [HttpGet]
    [Route("GetNoShape")]
    public string GetNoShape()
    {
        return "Property Injected: " + this.NoShape.Name;
    }

    [HttpGet]
    [Route("GetShapeCircle")]
    public string GetShapeCircle()
    {
        return "Property Injected: " + this.ShapeCircle.Name;
    }

    [HttpGet]
    [Route("GetShapeRectangle")]
    public string GetShapeRectangle()
    {
        return "Property Injected: " + this.ShapeRectangle.Name;
    }

    [HttpGet]
    [Route("GetPiValue")]
    public string GetPiValue()
    {
        return "Property Injected: " + this.PiValue;
    }

    [HttpGet]
    [Route("MethodInjected1")]
    public string InjectionMethod1()
    {
        return "Method Injected: " + this.MethodInjected1;
    }

    [HttpGet]
    [Route("MethodInjected2")]
    public string InjectionMethod2()
    {
        return "Method Injected: " + this.MethodInjected2;
    }

    [HttpGet]
    [Route("MethodInjected3")]
    public string InjectionMethod3()
    {
        return "Method Injected: " + this.MethodInjected3;
    }
}

In DIV2Controller.cs everything will be injected from the Dependency Configuration Resolver class

[RoutePrefix("api/v2/DIExample")]
public class DIV2Controller : ApiController
{
    private string ConstructorInjected;
    private string MethodInjected1;
    private string MethodInjected2;
    public string MyPropertyName { get; set; }
    public double PiValue1 { get; set; }
    public double PiValue2 { get; set; }
    public IShape Shape { get; set; }

    // MethodInjected
    [NonAction]
    public void Initialize()
    {
        this.MethodInjected1 = "Default Initialize done";
    }

    // MethodInjected
    [NonAction]
    public void Initialize2(string myproperty1, IShape shape1, string myproperty2, IShape shape2)
    {
        this.MethodInjected2 = myproperty1 + " & " + shape1.Name + " & " + myproperty2 + " & " + shape2.Name;
    }

    public DIV2Controller(string myproperty1, IShape shape1, string myproperty2, IShape shape2)
    {
        this.ConstructorInjected = myproperty1 + " & " + shape1.Name + " & " + myproperty2 + " & " + shape2.Name;
    }

    [HttpGet]
    [Route("constructorinjection")]
    public string constructorinjection()
    {
        return "Constructor Injected: " + this.ConstructorInjected;
    }

    [HttpGet]
    [Route("PropertyInjected")]
    public string InjectionProperty()
    {
        return "Property Injected: " + this.MyPropertyName;
    }

    [HttpGet]
    [Route("GetPiValue1")]
    public string GetPiValue1()
    {
        return "Property Injected: " + this.PiValue1;
    }

    [HttpGet]
    [Route("GetPiValue2")]
    public string GetPiValue2()
    {
        return "Property Injected: " + this.PiValue2;
    }

    [HttpGet]
    [Route("GetShape")]
    public string GetShape()
    {
        return "Property Injected: " + this.Shape.Name;
    }

    [HttpGet]
    [Route("MethodInjected1")]
    public string InjectionMethod1()
    {
        return "Method Injected: " + this.MethodInjected1;
    }

    [HttpGet]
    [Route("MethodInjected2")]
    public string InjectionMethod2()
    {
        return "Method Injected: " + this.MethodInjected2;
    }
}

Configuring the Dependency Resolver

public static void Register(HttpConfiguration config)
{
    var container = new UnityContainer();
    RegisterInterfaces(container);
    config.DependencyResolver = new UnityResolver(container);

    // Other Web API configuration not shown.
}

private static void RegisterInterfaces(UnityContainer container)
{
    var dbContext = new SchoolDbContext();
    // Registration with constructor injection
    container.RegisterType<IStudentRepository, StudentRepository>(new InjectionConstructor(dbContext));
    container.RegisterType<ICourseRepository, CourseRepository>(new InjectionConstructor(dbContext));

    // Set constant/default value of Pi = 3.141 
    container.RegisterInstance<double>("PiValueExample1", 3.141);
    container.RegisterInstance<double>("PiValueExample2", 3.14);

    // without a name
    container.RegisterInstance<IShape>(new NoShape());

    // with circle name
    container.RegisterType<IShape, Circle>("Circle", new InjectionProperty("Name", "I am Circle"));

    // with rectangle name
    container.RegisterType<IShape, Rectangle>("Rectangle", new InjectionConstructor("I am Rectangle"));

    // Complex type like Constructor, Property and method injection
    container.RegisterType<DIV2Controller, DIV2Controller>(
        new InjectionConstructor("Constructor Value1", container.Resolve<IShape>("Circle"), "Constructor Value2", container.Resolve<IShape>()),
        new InjectionMethod("Initialize"),
        new InjectionMethod("Initialize2", "Value1", container.Resolve<IShape>("Circle"), "Value2", container.Resolve<IShape>()),
        new InjectionProperty("MyPropertyName", "Property Value"),
        new InjectionProperty("PiValue1", container.Resolve<double>("PiValueExample1")),
        new InjectionProperty("Shape", container.Resolve<IShape>("Rectangle")),
        new InjectionProperty("PiValue2", container.Resolve<double>("PiValueExample2")));
}

User · Answer

I just watched the 30 minute Unity Dependency Injection IoC Screencast by David Hayden and felt that was a good explaination with examples   Here is a snippet from the show notes   The screencast shows several common usages of the Unity IoC  such as    Creating Types Not In Container  Registering and Resolving TypeMappings  Registering and Resolving Named TypeMappings  Singletons  LifetimeManagers  and the ContainerControlledLifetimeManager  Registering Existing Instances  Injecting Dependencies into Existing Instances  Populating the UnityContainer via App config   Web config  Specifying Dependencies via Injection API as opposed to Dependency Attributes  Using Nested   Parent-Child   Containers

User · Answer

Unity is a library like many others that allows you to get an instance of a requested type without having to create it yourself   So given   public interface ICalculator       void Add int a  int b      public class Calculator   ICalculator       public void Add int a  int b                return a   b            You would use a library like Unity to register Calculator to be returned when the type ICalculator is requested aka IoC  Inversion of Control   this example is theoretical  not technically correct    IoCLlibrary Register lt ICalculator gt  Return lt Calculator gt       So now when you want an instance of an ICalculator you just     Calculator calc   IoCLibrary Resolve lt ICalculator gt       IoC libraries can usually be configured to either hold a singleton or create a new instance every time you resolve a type   Now let s say you have a class that relies on an ICalculator to be present you could have    public class BankingSystem       public BankingSystem ICalculator calc                 calc   calc             private ICalculator  calc      And you can setup the library to inject a object into the constructor when it s created   So DI or Dependency Injection means to inject any object another might require

User · Answer

Unity is just an IoC  container   Google StructureMap and try it out instead  A bit easier to grok  I think  when the IoC stuff is new to you    Basically  if you understand IoC then you understand that what you re doing is inverting the control for when an object gets created    Without IoC    public class MyClass      IMyService  myService       public MyClass               myService   new SomeConcreteService                 With IoC container   public class MyClass      IMyService  myService       public MyClass IMyService myService              myService   myService               Without IoC  your class that relies on the IMyService has to new-up a concrete version of the service to use  And that is bad for a number of reasons  you ve coupled your class to a specific concrete version of the IMyService  you can t unit test it easily  you can t change it easily  etc    With an IoC container you  configure  the container to resolve those dependencies for you  So with a constructor-based injection scheme  you just pass the interface to the IMyService dependency into the constructor  When you create the MyClass with your container  your container will resolve the IMyService dependency for you    Using StructureMap  configuring the container looks like this    StructureMapConfiguration ForRequestedType lt MyClass gt    TheDefaultIsConcreteType lt MyClass gt     StructureMapConfiguration ForRequestedType lt IMyService gt    TheDefaultIsConcreteType lt SomeConcreteService gt       So what you ve done is told the container   When someone requests the IMyService  give them a copy of the SomeConcreteService   And you ve also specified that when someone asks for a MyClass  they get a concrete MyClass     That s all an IoC container really does  They can do more  but that s the thrust of it - they resolve dependencies for you  so you don t have to  and you don t have to use the  new  keyword throughout your code     Final step  when you create your MyClass  you would do this    var myClass   ObjectFactory GetInstance lt MyClass gt       Hope that helps  Feel free to e-mail me

User · Answer

MSDN has a Developer s Guide to Dependency Injection Using Unity that may be useful     The Developer s Guide starts with the basics of what dependency injection is  and continues with examples of how to use Unity for dependency injection   As of the February 2014 the Developer s Guide covers Unity 3 0  which was released in April 2013

User · Answer

Unity is an IoC  The point of IoC is to abstract the wiring of dependencies between types outside of the types themselves  This has a couple of advantages  First of all  it is done centrally which means you don t have to change a lot of code when dependencies change  which may be the case for unit tests    Furthermore  if the wiring is done using configuration data instead of code  you can actually rewire the dependencies after deployment and thus change the behavior of the application without changing the code

[c#] Can someone explain Microsoft Unity?

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