dependency injection presentation
TRANSCRIPT
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By
Reza Panah
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Inversion of Control (IoC) Programming to interfaces instead of
implementations
Instantiation of the services elsewhere (Notwhere and when they are used)
Separating Configuration from Use
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Itsa way to structure code so that we never
have to imperatively ask for DEPENDENCIES.Rather, we force consumers to supply them.
Dependency Inject in .Net by Mark Seemann
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publicclassUserController:Controller
{
[HttpPost]
publicActionResult Login(string username, string password)
{
var userRepository = newNHibernateUserRepository();
var found = userRepository.Find(userName,password).SingleOrDefault();if (found == null)
thrownewException("Invalid username or password");
FormsAuthentication.SetAuthCookie(username, false);
return Redirect("/User/Profile");
}
}
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publicclassUserController:Controller
{
publicIUserRepository UserRepository { get; set; }
[HttpPost]
publicActionResult Login(string username, string password)
{
var found = UserRepository.Find(username, password).SingleOrDefault();if (found == null)
thrownewException("Invalid username or password");
FormsAuthentication.SetAuthCookie(username, false);
return Redirect("/User/Profile");
}
}
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publicclassUserController:Controller
{
private readonlyIUserRepository userRepository;
publicUserController(IUserRepository userRepository)
{
this.userRepository = userRepository;
}[HttpPost]
publicActionResult Login(string username, string password)
{
var found = userRepository.Find(username, password).SingleOrDefault();
if (found == null)
thrownewException("Invalid username or password");FormsAuthentication.SetAuthCookie(username, false);
return Redirect("/User/Profile");
}
}
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A singlepoint in an application where theentire object graph is composed at once
It has access to the entire context, whichenables it to make intelligent decisions aboutwhich dependencies go where.
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Building loosely-coupled solutions Clean architecture
Maintainability (Extending the solution and fixingbugs easily)
Unit testing the right way Possibility of testing each service individually
Otherwise they are not called unit tests, they areintegration tests
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Constructor Injectionprivate readonlyIUserRepository userRepository;
publicUserController(IUserRepository userRepository)
{
this.userRepository = userRepository;
}
Setter Injection (Property Injection)publicIUserRepository UserRepository { get; set; }
Autowiring
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Service LocatorpublicclassUserController:Controller
{
[HttpPost]
publicActionResult Login(string username, string password)
{
var userRepository = ServiceLocator.Instance.GetObject();
var found = userRepository.Find(userName,password).SingleOrDefault();if (found == null)
thrownewException("Invalid username or password");
FormsAuthentication.SetAuthCookie(username, false);
return Redirect("/Contractor/Profile");
}
}
ServiceLocator is not Dependency Injection Coupling your consumers to the ServiceLocator Issues with unit testing
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Poor mans Injection (Bastard Injection)private readonlyIUserRepository userRepository;
publicUserController(IUserRepository userRepository)
{
this.userRepository = userRepository;
}publicUserController()
{
this.userRepository = new UserRepository();
}
It becomes very easy to violate Liskov SubstitutionPrinciple
Leads to a tightly-coupled system
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Spring.Net Ninject
StructureMap
Castle Windsor Unity
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A port of Java Spring framework Open source
Spring Source Community (Owned by VMWare)
Supports
Constructor injection Property injection Autowiring through constructor and property injection
(by type or by name)
XML Configuration (Spring CodeConfig was
launched in 2010 to allow configuration in code) Support for other framework such as NHibernate,
Spring.Net Messaging, AOP, etc
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Open source Fluent configuration
Very much extensible
Supports both constructor and propertyinjection
Autowiring as the main approach
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We wont have to make changes in thesolution
We are creating a small application and wedont need DI
There is an overhead
We dont need unit test
So what if we have to change every class to
add a minor functionality
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