Dependency Inversion Principle
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The document discusses the Dependency Inversion Principle (DIP), which states that high-level modules should not depend on low-level modules, both should depend on abstractions. It defines DIP and provides examples of how to implement dependency injection through interface injection, setter injection, and constructor injection. The key benefit of DIP is that it reduces coupling between modules and allows for loose coupling through abstraction.
Dependency Inversion Principle
- 1. Dependency Inversion Principle: Intro1
- 2. DIP: definitionDEPEND ON ABSTRACTION
- 3. DIP: definitionDO NOT DEPEND ON CONCRETE OBJECTS
- 4. DIP: definitionIT’S CALLEDINVERSION OF CONTROL............
- 5. DIP: definitionOR DEPENDENCYINJECTIONTOOOUT-SOURCING INDIA EFFECTS5
- 6. DIP: practical rules6No class should derive from a concrete classNo variable should hold a reference to a concrete classNo method should override an implementedmethod of any of its base class
- 7. DIP: Inversion of what ??7beforeafterInjectorConsumeralso high level componentdepends on an abstractionhigh level component depens on low level components (concrete classes)interfacenew()new()new()concrete classes depend on an abstractionDep1Dep2Dep2Dep1Dep2Dep2
- 8. DIP: a diagram8Take a look at the class diagramconcrete classes depend on an abstraction
- 9. DIP: Who9This guy is not a preacher or a wizard: Martin Fowler (*)He gave us three main styles(**) of dependency injection :Interface Injection Setter Injection Constructor Injection(*) but he is still waiting for a call from hollywood(**) and many other things...
- 10. DIP: Interface Injection (Type 1)10publicinterfaceIInjector {voidInjectDependency(IDependentdependent); }publicclassInjector : IInjector {privateIDependent_dependent; publicvoidInjectDependency(IDependentdependent) {_dependent = dependent; } publicvoidDoSomething() {_dependent.DoSomethingInDependent(); } }With this technique we define and use interfacesLet’s define an interface to perform injectionInjector implements the interface
- 11. DIP: Interface Injection (Type 1)11Get the correnct dependency based on config fileCreate our main class and inject the dependencythe method references the dependency, so behaviour depends on the config fileIDependentdependency = GetCorrectDependency();Injectorinjector = newInjector();injector.InjectDependency(dependency);injector.DoSomething(); Configuration file:<?xml version="1.0"encoding="utf-8" ?><configuration> <appSettings> <add key="ClassName"value="DIP.InterfaceInjection.DependentClass1" /> </appSettings></configuration>
- 12. DIP: Setter Injection (Type 2)12 publicclassInjector {privateIDependent_dependent;publicIDependentDependent {get { return_dependent; }set { _dependent = value; } }publicvoidDoSomething() {Dependent.DoSomethingInDependent(); } }Client class has a propertyCreate our main class and inject the dependencyIDependentdependency = GetCorrectDependency();Injectorinjector = newInjector();injector.Dependent = dependency;injector.DoSomething();
- 13. DIP: Constructor Injection (Type 3)13 publicclassInjector {privateIDependent_dependent;publicInjector(IDependentdependent) {_dependent = dependent; }publicvoidDoSomething() {_dependent.DoSomethingInDependent(); } }Client class has nothins else a constructor to inject dependencyCreate our main class and passing dependencythrough constructorIDependentdependency = GetCorrectDependency();Injectorinjector = newInjector(dependency);injector.DoSomething();
- 14. DIP: Links and conclusions14Inversion of Control Containers and the Dependency Injection pattern Introduction to Dependency Injection by Rich Newman Images from Wacky.com
Editor's Notes
- #2: Dependency inversion principle