Depth Consulting - Calgary .NET User Group - Apr 22 2015 - Dependency Injection
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This document summarizes a presentation on dependency injection. It begins with an introduction to dependency injection, describing it as providing objects their dependencies rather than having them construct dependencies themselves. It then discusses the different ways dependencies can be injected through constructor or property injection. It also covers the different types of dependencies that can be injected, such as interfaces or concrete classes. The presentation demonstrates dependency injection with a code example and discusses how dependency injection containers can help manage object lifecycles and make development easier. It acknowledges some challenges with dependency injection but emphasizes that it leads to better design, testability and code quality.
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Depth Consulting - Calgary .NET User Group - Apr 22 2015 - Dependency Injection
- 2. http://www.depthconsulting.ca Developer Fundamentals : The Series Calgary .NET User Group Dependency Injection What You Need to Know Dave White Microsoft MVP – Visual Studio ALM
- 3. http://www.depthconsulting.ca Developer Fundamentals Series Testing – Nov. 26, 2014 SOLID – Feb. 26, 2015 Dependency Injection – April 22, 2015 Source Control – Branching/Merging – June Putting It All Together – July
- 4. http://www.depthconsulting.ca Dave White Principal Consultant – Depth Consulting http://linkd.in/giMxuw @AgileRamblings • In IT for over 15 years • Microsoft MVP – Visual Studio ALM (2 years) • Kanban/Agile Evangelist, Speaker • PRDC 2011, 2012, LKUK, Local events • Program Director – KCP Program - LKU • Professional Scrum Master • Microsoft Platform Developer (C#, Web, WPF) http://www.agileramblings.com
- 5. http://www.depthconsulting.ca Simon Timms Senior .NET Dev – Pacesetter Directional Drilling http://linkd.in/15pYAWL @stimms • In IT for over a decade (+/− few months) • Microsoft MVP – ASP.NET/IIS (2 years) • Prolific Speaker and Community Involvement • PRDC (many), AzureCamp, Local events • Calgary .NET User Group – President • Author • Loves Development • Polyglot • Web apps, .NET back ends • Visualization and Cloud http://blog.simontimms.com/about/
- 7. http://www.depthconsulting.ca Why We Don’t Inject • I don’t test design • No one around me is doing it • Too hard to learn • No tools • My stuff doesn’t need it • Our code is horrible and very deeply coupled • No time
- 8. http://www.depthconsulting.ca The truth of the matter… • I makes testing designing easier! • It encourages SOLID principles • Everyone is doing it • Easier than ever • Investment in tools • Private and OSS • You can start small • You will be a better developer • Drives growth down maturity path • Increasing Complexity • Business and technical • It makes you faster
- 9. http://www.depthconsulting.ca Let’s start learning! By John Castillo (Jack) (https://creativecommons.org/licenses/by/2.0/deed.en), via Wikimedia Commons
- 10. http://www.depthconsulting.ca What is Dependency Injection (DI) Short: Giving an object it’s instance variables Medium: Dependency injection is providing the objects that an object needs (its dependencies) instead of constructing them itself Long: Dependency injection is a software design pattern in which one or more dependencies (or services) are injected, or passed by reference, into a dependent object (or client) and are made part of the client's state. http://en.wikipedia.org/wiki/Dependency_injection James Shore - http://bit.ly/1cUUGaA
- 11. http://www.depthconsulting.ca Two Ways to Inject Constructor • explicitly required • “I cannot function without this” Property (Setter) • optionally required • “I can function without this” public class MyClass { public void MyClass(IDependentOn dependency) { } } public class MyClass { public void MyClass() { } public IDependentOn dependency {get; set;} }
- 12. http://www.depthconsulting.ca Two Types of Things to Inject Concrete Classes • less flexible • can only inject single implementation Interfaces • more flexible • can inject multiple implementations public class MyClass { public void MyClass(DependentOn dependency) { } } public class DependentOn {} public class MyClass { public void MyClass(IDependentOn dependency) { } } public interface IDependentOn {} public class Concrete1: IDependentOn {} public class Concrete2: IDependentOn {}
- 14. http://www.depthconsulting.ca By Deutsche Fotothek [CC BY-SA 3.0 de (http://creativecommons.org/licenses/by-sa/3.0/de/deed.en)], via Wikimedia Commons That doesn’t look so hard but why again?
- 15. http://www.depthconsulting.ca Encourages Modularity • Makes testing designing easier • S in SOLID is good • Decomposing functionality into smaller parts is good • Freeing yourself from some concerns which is good • Allows implementation flexibility (good) • Centralized implementation (good) • Reduces Ctrl-C / Ctrl-V code reuse (good)
- 16. http://www.depthconsulting.ca Remember • You are reading this because you want to improve • You’ve learned about testing design • You’ve learned about SOLID • These things should be viewed as a holistic improvement They all support each other
- 17. http://www.depthconsulting.ca By Venpia (Own work) [CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons So… there are tools to make this easier?
- 18. http://www.depthconsulting.ca Dependency Injection Containers http://lmgtfy.com/?q=dependency+injection Castle Windsor - Unity StructureMap
- 19. http://www.depthconsulting.ca What do Containers Provide • Primary Functions • Registration • Resolution • Manage Lifetime • Secondary Functions • Interception/AOP • Assembly Loading/Type Discovery
- 20. http://www.depthconsulting.ca Registration • Enables container to know what to create • Describes construction intent • What concrete classes are associated with requests • Singleton, always create new instances, instance per scope (request) • Interception
- 21. http://www.depthconsulting.ca Resolution • Construct the actual instances as required • Add interceptors (more later)
- 22. http://www.depthconsulting.ca Manage Lifetime • If construction is a primary responsibility, so is destruction
- 23. http://www.depthconsulting.ca Interception • You can do AOP with containers • Usually require an extension
- 24. http://www.depthconsulting.ca Assembly Loading/Type Discovery • Some containers have helper functions that discover implementation classes that fit a specific criteria • Attributes, Interfaces implemented
- 26. http://www.depthconsulting.ca Hold on a second here Mister! By Achim Hering (Own work) [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-3.0 (http://creativecommons.org/licenses/by/3.0)] via Wikimedia Commons
- 27. http://www.depthconsulting.ca The Real Truth - It Can’t Be All Roses• Dependency Inject is often a breaking change • Not a refactoring: • New application architecture pattern in your application • Burdened by a MOUNTAIN of technical debt and bad design • It requires a better understanding of • SOLID and the chosen container’s API • You’re whole team has to understand it • You may have to seek permission from your teammates • Not managers • Dependency graphs aren’t any more
- 28. http://www.depthconsulting.ca The Real Truth – There ARE Roses • Making Unit Tests will be easier • You will create higher quality product • You will create better designs • Most (all?) of the container implementations are OSS (read: free)
- 29. http://www.depthconsulting.ca We can do this! By Weird Beard – Happy [CC-BY-2.0 (http://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons
- 30. http://www.depthconsulting.ca Next Steps • Build an example application • Understand what you want from a DI Container • Try multiple containers that fulfill your requirements • Share your learning with your team KEEP CALM and DI/SOLID/TES T ON
- 31. http://www.depthconsulting.ca Tools • Visual Studio Community http://www.visualstudio.com/products/visual-studio-community-vs • Visual Studio 2015 Preview http://www.visualstudio.com/en-us/news/vs2015-preview-vs • Nuget • Autofac, Moq • http://www.autofac.org • https://github.com/Moq/moq4 PM> Install-Package Autofac PM> Install-Package Moq
- 32. http://www.depthconsulting.ca These are the MeetUps you’re looking for… Testing – Nov. 26, 2014 SOLID – Feb. 26, 2015 Dependency Injection – April 22, 2015 Source Control – Branching/Merging – June Putting It All Together – July
- 33. http://www.depthconsulting.ca City of Calgary - Hackathon
- 34. http://www.depthconsulting.ca NOW PRIZES!! 1 ReSharper licence https://www.jetbrains.com/resharper/ 1 Infragistics Ultimate License http://www.infragistics.com/ INFRAGISTICS ULTIMATE