Is dependency injection is the only way to achieve loose coupling in c#
?? I have been going through injection (DI), to solve the tight coupling, I found DI as one solution for that ! Buy I'm looking for other solutions even
your question is a bit abstract. you first need to define your problem.
But, in order to write a loosely coupled, you'll need to use abstractions and not implementations (so you can inherit and override whatever you want) and inject the abstractions with dependency injection to your class/methods.
that way you are not coupled to the specific implementation of the code and whoever wants can just implement the interface and pass it to the class/method.
Related
sorry for what might be a poor question but I am a bit confused.
Would TDD help ensure DI? or is it the other way around (DI is required for TDD).
TDD is a method to design and develop a software.
Dependency injection is a technique to allow selection among multiple implementations of a given dependency interface at run time or at compile time.
While one might argue that these two are independent, doing TDD without DI is possible, but difficult. Therefore, I would say that doing TDD for the medium to large projects does require dependency injection.
This is actually a very good question.
I would say nothing in TDD's DNA makes it intrinsically related to Dependency Injection. It just so happens that the Refactoring step in TDD sometimes leads to extracting behavior to an external dependency, which can then optionally be injected into the class under test via its constructor. Nothing systematic though, how to manage dependencies is more a matter of the refactorer's own taste.
The reverse is also true - nothing in DI forces you to write your code with a TDD approach. DI improves testability indeed but that doesn't necessarily imply test-first nor the Red-Green-Refactor cycle.
However, later refinements/specializations of TDD like Outside-In TDD do make intensive use of Dependency Injection, and TDD practitioners are also typically proponents of SOLID principles which include Dependency Inversion at their core. Popular tools like isolation and auto-mocking frameworks combine TDD and DI as well. This may be why the 2 practices are often seen used and talked about together.
Neither.
TDD should help design better software.
A better design might use the inversion of control pattern
DI is an implementation of the IOC pattern
IoC = Inversion Of Control
DIP = Dependency Inversion Principle (D in S.O.L.I.D.)
IoC == DIP? I think so, is true.
The world of building software is already so messy, why so many words to say the same thing?
(I know DI (Dependency Injection) and it is different of DIP and IoC)
Update:
According to the answers, then we can say that: (DI) + (IoC) = (Dependency Inversion Principle) ?
Inversion of Control is the generic term. Dependency Injection is a specific type of IoC.
See Inversion of Control Containers and the Dependency Injection pattern.
The Dependency Inversion Principle is a guideline, while the other terms are descriptive of techniques. (IoC can be used to describe a principle as well, so this can be confusing.)
Used in a sentence:
Sue followed the Dependency Inversion Principle by using Dependency
Injection in the constructor of her class and creating instances with
an Inversion of Control container.
Update:
I do not feel that (DI) + (IoC) = (Dependency Inversion Principle) is accurate. That's like saying (Apple) + (Food) = (Good Nutrition). Each term has a specific meaning.
I don't think you're going to get an authoritative answer on this one because the term "IoC" is kind of overloaded and to say "the one true meaning of IoC is..." is kind of pedantic. But I'll share my opinion anyway :)
Dependency Inversion is about depending on an abstraction. Consider a HelloWorld class that depends on an IStringWriter, and an implementation class ConsoleStringWriter.
Inversion of Control is when the framework/infrastructure invokes application code, rather than the other way around. For example, when a user closes a WPF app, you don't call the framework, it raises an event that you can subscribe to.
They are often combined. For example, Hibernate depends on the abstraction defined by its Interceptor interface in order to implement IoC. From an Interceptor's point of view, control is inverted - Hibernate calls the Interceptor. Another example you see all over is IHandle<T> where T is an Event or a Command or a Message - the infrastructure calls the handler at the right time.
Its confusing because we call them "IoC containers", but you can do DI without doing IoC. If you inject a ConsoleStringWriter into a HelloWorld I don't really think of this as IoC because there is no "framework" or "infrastructure". But that's because Hello World is trivial - as an application becomes more complex the need for IoC increases.
See also this question and accepted answer.
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Inversion of Control < Dependency Injection
I always read IoC(Inversion of Control) and DI(Dependency Injection) in the same context. What is exactly the difference between IoC and DI? How does IoC differ from DI?
In common usage, the terms have become somewhat synonymous. The original idea of IoC -- Inversion of Control -- was very much related to the "Hollywood Principle:" Don't Call Us, We'll Call You.
In traditional applications, developers would write business code and framework code. The business code would then call the framework code to accomplish tasks. Under an IoC model, you "invert" that model and create a framework that accepts business modules and calls them to accomplish tasks. This principle is exhibited in several development frameworks including the old Smart Client Software Factory and the newer Prism (or Composite Applications for WPF/Silverlight). In these models, the UI Modules are registered with an IoC Container and loaded as needed based on configuration and user actions. While powerful, these models also tend to have a very steep learning curve.
Dependency Injection is a technique (hard to call it a pattern, really) of removing internal dependencies from implementations by allowing dependent objects to be injected into the class/method by an external caller. IoC frameworks use dependency injection to supply user modules and other dependent code to framework routines that "glue it all together." Dependency injection is used heavily by IoC frameworks because that is the mechanism that allows them to "Call You."
IoC Containers, such as Castle Windsor and Structure Map help with dependency injection by providing automatic instantiation and lifecycle management of classes you register -- including automatic instantiation and injection of parameters required by registered classes. All of this makes it easier to use dependency injection, but is not required.
Dependency Injection is a mechanism for flexibility that maximizes dependency on Interfaces while minimizing dependency on specific implementation. Consequently, systems that use dependency injection can support "pluggable" implementation classes that can be used depending on circumstances. A very big benefit of this "pluggability" is that it makes creating Unit Tests much easier. You can mock an object to the needed interface, then inject it into your test object.
So, IoC is really the broader principle and DI is a fundamental technique within. IoC (Hollywood Principle) systems tend to be pretty complex, can be hard to understand, and thus have steep learning curves. DI, on the other hand is a good practice for everyday developers. I tend to prefer understandable and clear over cool, but complex.
IoC is the ability to vary the implementation of a contract.
DI is the ability to supply the implementation.
When I'm doing TDD, it forces me to employ Dependency Injection principle and I end up with loosely coupled code.
I was told that it's harder to understand application that has loosely coupled code.
Can you tell me what pros and cons of loosely coupled code?
The biggest advantage is that introducing changes to one module does not break other modules in unpredictable ways.
Dependency Injection does not automatically lead to low coupling. I agree with the answers above about the pros of low coupling. The main benefits of Dependency Injection is that it improves testability and that it helps you follow the GoF principle of Program to Interfaces, not Implementations. But you can have high coupling to injected dependencies too.
The other benefit is being able to replace components more easily when you have more than one implementation.
Imagine you have a shopping cart system, it normally stores and reads from a database, that's the default. But you can inject so that it uses a backend, which is not as good but it works when you don't have a database.
Since it's loosely coupled, it's highly changeable. That's the whole point. If you don't need that, the loose coupling may introduce many indirections that result in a system with more 'depth': you need to look down a level in order to see all that happens.
Like you said, the cons of loosely coupled code are increased complexity, and it's difficulty to understand. It's usually not immediately apparent what the code does when it's loosely coupled.
Like others have said: The benefit is that it's much easier to swap other pieces of code/modules/objects/components when the pieces aren't dependent on one another.
As with all OO design, there are trade offs you have to make - is it more important for you to have highly modular code that is easy to swap in and out? Or is it more important to have easily understandable code that is simpler? You'll have to decide that.
Reuse, extensibility and a reduction in side-effects.
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Lately I have seen a lot of blog posts concerning how to build loosely coupled applications. Which patterns do you use most when creating loosely coupled applications? Dependency Injection? Inversion of Control?
Model-View-Controller.
Aside: things that stops me writing coupled applications aren't just patterns:
Naming. If I can't easily think of a name for my class, it either does nothing or too many things.
Testability. If I can't easily mock out my class' dependencies, it's a coupled design.
I find myself using the Command pattern quite often. It's a pattern that just keeps giving project after project.
Dependency injection with spring is my favourite. Additionally with maven it's common to do this really neat trick of hiding all the implementations behind an API module. So if your code has three modules, "application-core", "externalsystems-api" and "externalsystems", you can make "application-core" depend ONLY on externalsystems-api. The actual-implementations and all their dependencies can be totally invisible to the application-core module. This really enforces a much harder separation of concerns and makes loose coupling easier.
The neat thing is that IDEs that load these maven setups enforce these visibility constraints. So you're not going to be able to reference SQL, AXIS, JAXB or whatever in your application-core
Some of the SOA related patterns (enterprise service bus for example) offer abstraction at a higher level and support separation of concerns across business services and technical services. Loose coupling between the services is then (arguably) supported by introducing a broker or bus that de-couples the services in the solution.
Visitor pattern works quite well
I think one of the fundamental techniques is "Tell Don't Ask Principle, Law Of Demeter". Maybe it is not like DI,UI or other Desing Patterns but I think objects that fallow this principle are loosely coupled and do the one thing well.
"Keep It Shy Keep It Dry Tell The Other Guy"
Yes, the important ones are Dependency Injection and Inversion of Control, but lets not forget the Abstract Factory and Registries.
Bridge pattern (http://en.wikipedia.org/wiki/Bridge_pattern)
Dependency Injection is a form of Inversion-of-control.
The Spring Framework has a large base of Java programmers, and it has a .NET implementation, too.
The Strategy Pattern.
I'm surprised this hasn't been mentioned yet - strategies allow you to avoid creating classes that know too much about different types in your domain model. Each strategy is responsible for codifying a particular interaction involving specific types. This avoids creating a master type that is aware of many others and the nuances of the implementation of each.
From Wikipedia:
The strategy pattern uses composition
instead of inheritance. In the
strategy pattern behaviors are defined
as separate interfaces and specific
classes that implement these
interfaces. Specific classes
encapsulate these interfaces. This
allows better decoupling between the
behavior and the class that uses the
behavior. The behavior can be changed
without breaking the classes that use
it, and the classes can switch between
behaviors by changing the specific
implementation used without requiring
any significant code changes.
Behaviors can also be changed at
run-time as well as at design-time.
Dependency injection and IOC are both excellent for decoupling code.
Dotnetrocks show 362 provides very good definitions. Also watch the related DNR TV episode to get a clearer understanding.
Dependency injection is the pattern that I use in nearly all classes that I write - if the class has a dependency, I always inject it (using constructor injection). Only classes which have no dependencies (i.e. value objects) don't use the DI pattern. Being able to test classes which use DI is a major benefit.
For information on the benefits of DI, these two presentations are very good:
http://googletesting.blogspot.com/2008/11/clean-code-talks-dependency-injection.html
http://googletesting.blogspot.com/2008/11/clean-code-talks-global-state-and.html
No DI container is needed to use the DI pattern, but when the program becomes big (tens of classes or many scopes), then a DI container can reduce much boilerplate. On the JVM my default choice is Guice.
Inversion of Control as overall code/architecture style.
DI as a mechanism to configure IoC.
Local abstractions (I call this "Ideal Environment Development" - write as if you had the exact environment you wanted).
Objects typically communicate using void methods, and by passing data, rather than having getters/setters.
I never use a dependency directly in a core business class - it is always abstracted to a local abstraction, and an explicit Bridge deals with the dependency.
I've found that this combination allows for extremely flexible code with a very compositional feel to it.