?
Solved

MVC tutorial: I don't understand a syntax for Dependency Injection

Posted on 2011-02-16
1
Medium Priority
?
518 Views
Last Modified: 2013-12-17
I am using the tutorial below but I don't understand this syntax on the code:
public ContactController()
            : this(new EntityContactManagerRepository())
        {}
http://www.asp.net/mvc/tutorials/iteration-4-make-the-application-loosely-coupled-cs

using System.Text.RegularExpressions;
using System.Web.Mvc;
using ContactManager.Models;

namespace ContactManager.Controllers
{
    public class ContactController : Controller
    {
        private IContactManagerRepository _repository;

        public ContactController()
            : this(new EntityContactManagerRepository())
        {}


        public ContactController(IContactManagerRepository repository)
        {
            _repository = repository;
        }

        
        protected void ValidateContact(Contact contactToValidate)
        {
            if (contactToValidate.FirstName.Trim().Length == 0)
                ModelState.AddModelError("FirstName", "First name is required.");
            if (contactToValidate.LastName.Trim().Length == 0)
                ModelState.AddModelError("LastName", "Last name is required.");
            if (contactToValidate.Phone.Length > 0 && !Regex.IsMatch(contactToValidate.Phone, @"((\(\d{3}\) ?)|(\d{3}-))?\d{3}-\d{4}"))
                ModelState.AddModelError("Phone", "Invalid phone number.");
            if (contactToValidate.Email.Length > 0 && !Regex.IsMatch(contactToValidate.Email, @"^[\w-\.]+@([\w-]+\.)+[\w-]{2,4}$"))
                ModelState.AddModelError("Email", "Invalid email address.");
        }

        public ActionResult Index()
        {
            return View(_repository.ListContacts());
        }

        public ActionResult Create()
        {
            return View();
        } 

        [AcceptVerbs(HttpVerbs.Post)]
        public ActionResult Create([Bind(Exclude = "Id")] Contact contactToCreate)
        {
            // Validation logic
            ValidateContact(contactToCreate);
            if (!ModelState.IsValid)
                return View();

            // Database logic
            try
            {
                _repository.CreateContact(contactToCreate);
                return RedirectToAction("Index");
            }
            catch
            {
                return View();
            }
        }

        public ActionResult Edit(int id)
        {
            return View(_repository.GetContact(id));
        }

        [AcceptVerbs(HttpVerbs.Post)]
        public ActionResult Edit(Contact contactToEdit)
        {
            // Validation logic
            ValidateContact(contactToEdit);
            if (!ModelState.IsValid)
                return View();

            // Database logic
            try
            {
                _repository.EditContact(contactToEdit);
                return RedirectToAction("Index");
            }
            catch
            {
                return View();
            }
        }

        public ActionResult Delete(int id)
        {
            return View(_repository.GetContact(id));
        }

        [AcceptVerbs(HttpVerbs.Post)]
        public ActionResult Delete(Contact contactToDelete)
        {
            try
            {
                _repository.DeleteContact(contactToDelete);
                return RedirectToAction("Index");
            }
            catch
            {
                return View();
            }
        }

    }
}

Open in new window

0
Comment
Question by:DistillingExperts
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
1 Comment
 
LVL 52

Accepted Solution

by:
Carl Tawn earned 2000 total points
ID: 34908713
Your code contains two contructors. One accepts an IContactManagerRepository object, which allows you to "inject" any object you like that implements that interface. The idea is that your controller isn't hard-coded to work with a particular concrete repository object.

The second constructor simply creates a default EntityConactManagerRepository object. So, if you don't specify otherwise then that is the type of repository that will be used. The "injection" part is implemented in the first constructor because it allows you to determine what type of repository to use rather than hard-coding a specific type.

Hope that makes some sense :)
0

Featured Post

Application Discovery Service in AWS

In the era of the cloud, customers migrating away from their existing on-premise infrastructure. This requires lots of planning, strategies, and effort to identify their existing resources and determine how best to migrate.  Datacenter migrations happen in four phases -

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Entity Framework is a powerful tool to help you interact with the DataBase but still doesn't help much when we have a Stored Procedure that returns more than one resultset. The solution takes some of out-of-the-box thinking; read on!
International Data Corporation (IDC) prognosticates that before the current the year gets over disbursing on IT framework products to be sent in cloud environs will be $37.1B.
This is my first video review of Microsoft Bookings, I will be doing a part two with a bit more information, but wanted to get this out to you folks.
This tutorial will teach you the special effect of super speed similar to the fictional character Wally West aka "The Flash" After Shake : http://www.videocopilot.net/presets/after_shake/ All lightning effects with instructions : http://www.mediaf…
Suggested Courses

764 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question