Dependency Injection in ASP.NET 5

Dependency injection is a software design pattern that implements inversion of control and allows a program design to follow the dependency inversion principle. An injection is the passing of a dependency (a service) to a dependent object (a client). The service is made part of the client’s state. Passing the service to the client, rather than allowing a client to build or find the service, is the fundamental requirement of the pattern. The pattern is used to create program designs that are loosely coupled and testable.

Types of Dependency Injection

  • Constructor injection: the dependencies are provided through a class constructor. – ASP.NET 5 supports only this.
  • Setter injection: the client exposes a setter method that the injector uses to inject the dependency.
  • Interface injection: the dependency provides an injector method that will inject the dependency into any client passed to it. Clients must implement an interface that exposes a setter method that accepts the dependency.

In ASP.NET 5, dependency injection is a first class citizen. While in the previous versions of the framework, DI was partially supported, in ASP.NET 5 it is available throughout the entire stack. A minimalistic DI container is provided out of the box, but you can use your own container (BYOC – Bring Your Own Container support).

The default dependency injection supports following life styles.

Lifestyle Description
Instance A specific instance is given all the time. You are responsible for its initial creation
Transient A new instance is created every time
Singleton A single instance is created and it acts like a singleton
Scoped A single instance is created inside the current scope. It is equivalent to Singleton in the current scope

A popular feature for DI in web applications is to create objects that have a single instance per web request. This means that the objects acts as a singleton inside that request but two distinct requests will have different instances of the objects.

In this post, I am injecting database repository to the controller with scoped life style – runtime will create instance of repository on every web request. Here is the changes required in the Startup.cs.

public void Configure(IApplicationBuilder app)
{
	app.UseErrorPage();
	app.UseServices(services =>
	{
		services.AddMvc();
		services.AddScoped<IUserRepository, UserRepository>();
	});

	app.UseMvc();
}

And in the controller, create a constructor, which accepts IUserRepository parameter, which will be injected by runtime while creating the instance of contolller.

public class HomeController : Controller
{
	private IUserRepository _userRepository;
	public HomeController(IUserRepository userRepository)
	{
		_userRepository = userRepository;
	}
	
	public ActionResult Index()
	{
		return View(_userRepository.Users()); 
	}
}

Here is the IUserRepository interface and its implementation.

public interface IUserRepository
{
	List<User> Users();
}
	
public class UserRepository : IUserRepository
{
	public List<User> Users()
	{
		var listOfUsers = new List<User>();
		for(int i = 0; i< 10; i++)
		{
			listOfUsers.Add(new User(){ Name = "User " + i });
		}
		
		return listOfUsers;
	}
}

public class User
{
	public string Name { get;set; } 
}

You can find more details about Dependency Injection in ASP.NET vNext here

Happy Programming :)

New C# 6.0 features

As part of the Connect(); event, Microsoft introduced VS2015 Preview, which includes C# 6.0 with few more features. (These features are not included in my earlier post What is new in C# 6.0, as I already mentioned these features introduced by Microsoft in the Connect(); event few days back.)

  • nameof operator – nameof operator allows developers to use program elements as text. In MVVM project, you are using property notifications, it is recommended to use strongly typed property notifications, instead of string. Because you are hard coding the property name, if you rename the property, you need to change the string manually. The nameof operator helps you to use the property as the parameter.
    public string FirstName
    {
        get { return _firstName; }
        set
        {
            if (_firstName != value)
            {
                _firstName = value;
                OnPropertyChanged(nameof(FirstName));
            }
        }
    }
    

    Runtime will replace the property with the property name while generating the IL code.

    IL code generated for nameof operator

    IL code generated for nameof operator

  • null conditional dot operator – as the name indicates it for null checking. This helps you to make null checking fade into the background.
    static void PrintBook(Book book)
    {
        var name = book.Name;
        var price = book.Price;
        Console.WriteLine("Name :{0} - Price {1}", name, price);
    }
    

    I have a function like this, which will print the name and price of the book. Please note I am not doing any null check, if the book instance is null, it will throw exception. The null conditional dot operator helps to avoid this validation and processing. If you are invoking a property of null object instance, it will return null for that property as well, it won’t throw null reference exception.

    static void PrintBook(Book book)
    {
        var name = book?.Name;
        var price = book?.Price;
        Console.WriteLine("Name :{0} - Price {1}", name, price);
    }
    

    In case of value types, Visual Studio will treat the type of the variable as nullable, if you use null conditional dot operator.

    null conditional dot operator - with value types

    null conditional dot operator – with value types

  • string interpolation – Another cool feature, which will help you to manage string formatting easy. In the current framework, you need use string.Format function, it little complex, you need to put numeric place holders ({n}) and based on the number you need to set the variables. String Interpolation will help developers to use actual variables as placeholders.
    var message = string.Format("Book Name :{0} Price :{1}", name, price);
    

    Can be re-write like this.

    var message = "Book Name :\{name} Price :\{price}";
    

    It supports IntelliSense for the variable names, also variables can be identified with different color.

    String Interpolation - IntelliSense

    String Interpolation – IntelliSense

You can download VS 2015 Preview from here

Happy Coding :)

First look into Visual Studio Community 2013

Yesterday Connect(); Event, Scott Guthrie and Soma Somasegar made a number of important announcements for the cloud-first, mobile-first developer. Visual Studio Community 2013 is a new free, fully-featured edition of Visual Studio that lets developers target any platform, from desktop and mobile to web and cloud.

Visual Studio Community 2013

Visual Studio Community 2013

Visual Studio Community 2013 also supports full Visual Studio extensibility, offering access to the ecosystem of over 5000 extensions. You can download it from here. You can also try Visual Studio Community 2013 in Azure VM image.

What is new in Visual Studio Community 2013

  • Professional-grade editing, code analysis, and debugging support – Your favourite Refactor and Debugging features are included.
  • Support for open-source workflows (Git).
  • Compilers for managed languages, C++ and more
  • Cross-platform mobile development including the web, Android, iOS, and Windows Phone with the free Visual Studio Tools for Apache Cordova extension.
  • Take advantage of cloud services with simplified Azure SDK integration, and incorporate modern app analytics and telemetry with Application Insights. Application Insights collects, processes and presents a wide variety of telemetry including performance, usage, availability, exception, crash, environment, log and developer-supplied data from all components of a modern application – including clients (devices and browser), servers, databases and services.
    Application Insights

    Application Insights

  • Access to all the Visual Studio 2013 extensions on the Visual Studio Gallery

Visual Studio Community 2013 includes Update 4, which is a cumulative update of all previous Visual Studio 2013 updates.

Happy Programming :)

POCO controllers in ASP.NET vNext

As part of ASP.NET MVC 6, Microsoft introduced POCO(Plain Old CLR Object) Controllers. Unlike MVC 5 or previous versions of MVC, POCO contollers, has no base class, no need to implement any interface, it is 100% convention.

POCO controller implementation.

using Microsoft.AspNet.Mvc;

public class HomeController
{
	public ActionResult Index()
	{
		return new ViewResult() { ViewName = "Index" };
	}
}

As long as your class is public, non-abstract, has a Controller suffix and is defined in an assembly that references any of the MVC assemblies (Microsoft.AspNet.Mvc.Core, Microsoft.AspNet.Mvc etc), it will be discovered as a valid controller.

Injecting services

using Microsoft.AspNet.Mvc;
public class HomeController
{
    [Activate]
    public ViewDataDictionary ViewData { get; set; }

    public ActionResult Index()
    {
        return new ViewResult() { ViewData = ViewData };
    }
}

The Activate attribute will help ASP.Net runtime to inject various services to the controller. You can use ViewDataDictionary.Model property for passing Model to view in POCO controllers.

Happy Programming :)