Dependency Injection and Model-View-Controller

Overview

Inversion of ControlModel-View-Controller

Why Inversion of Control?

Procedural logic leads to tight coupling to particular implementations

Inversion of control pushes logic to the lower application layers

Essential coupling remains

Binding to Concrete Instances

Factory instantiationConstructor instantiationConfiguration based instantiation

Dependency Injection

Container InjectionRuntime bindingFacilitates testingSimpler than factory construction?Looser coupling

Simple Container Example

Plug-in ManagerType is requestedLookup for type to be loadedReflection used to find the typeInstantiates an instance and returns itTest and Code use different Data Mapper 

Dependency Injection Problems

Complex level of indirectionCode can be difficult to read and understandUse at component boundariesLevel of testing is an economic judgment

Model View Controller

Separate user interface from business logicModel has no User Interface interactionController handles input events from user

interfaceView represents the appropriate display of the

model

Advantages of MVC

User interfaces are hard to testKeeps UI level smallMakes business logic easier to testUI can be modified without affecting business

logic

Summary

Inversion of Controlminimizes couplingdependency injection for runtime control

Model View Controllerdecouples UI from business logicflexible testing and evolution