Dependency Injection in .NET [Full-Day Workshop]

Loosely coupled code is easier to maintain, extend, and test. Dependency Injection (DI) help us get there. In this workshop, we'll see how interfaces can add "seams" to our code that makes it more flexible and maintainable. From there, we'll dig into loose coupling with Dependency Injection. DI doesn't have to be complicated. With just a few simple changes to our constructors or properties, we can have code that is easy to extend and test. After laying a good foundation, we'll take a closer look by diving into various DI patterns (such as constructor injection and property injection) as well as other patterns that help us handle interception and optional dependencies. Along the way, we'll see how DI helps us adhere to the SOLID principles in our code. We'll also we'll look at common stumbling blocks like dealing with constructor over-injection, managing static dependencies, and handling disposable dependencies. Throughout the day, we'll go hands-on with labs to give you a chance to put the concepts into action. If you're a C# developer who wants to get better with concepts like abstraction, loose coupling, extensibility, and unit testing, then this is the workshop for you.

Prerequisites

To get the most out of the workshop, you should have an understanding of the basics of C# and object oriented programming (classes, inheritance, methods, and properties). No prior experience with dependency injection is necessary. Hardware & Software To participate in the hands-on portion, you will need a computer (Windows, macOS, or Linux) with the following installed:

• .NET Core 3.1 SDK
  https://dotnet.microsoft.com/download
  The .NET Core SDK (Software Development Kit) allows you to build .NET applications.
• Visual Studio Code
  https://code.visualstudio.com/download
  This is a great all-around editor.
• VS Code C# Extension
  https://marketplace.visualstudio.com/items?itemName=ms-dotnettools.csharp
  This extension to Visual Studio Code adds syntax highlighing and code completion for C#.
• VS Code Live Share Extension Pack
  https://marketplace.visualstudio.com/items?itemName=MS-vsliveshare.vsliveshare-pack
  This extension to Visual Studio Code will allow you to connect to my development environment where we can share code and develop together.

As an alternative, you can use Visual Studio 2019 (any edition). No additional extensions are required. Live Share is built in to current versions of Visual Studio.

Labs

These are the hands-on portions of the workshop. Labs can be completed with Visual Studio Code or Visual Studio 2019. All labs run on Windows, macOS, and Linux. Each lab consists of the following:

• Labxx-Instructions (Markdown)
  A markdown file containing the lab instructions. This includes the scenario, a set of goals, and step-by-step instructions.
  This can be viewed in on GitHub or in Visual Studio Code (just click the "Open Preview to the Side" button in the upper right corner).

• Starter (Folder)
  This folder contains the starting code for the lab.

• Completed (Folder)
  This folder contains the completed solution. If at any time, you get stuck during the lab, you can check this folder for a solution.

Other Demos

The other folders contain samples that are shown during the lecture portions. This code is runnable with Visual Studio Code or Visual Studio 2019; however, these samples are Windows-only. The demos are as follows:

1. Overview MainDemo-Basics
   An overview of the what and why of dependency injection. Breaking tight coupling allows changing the data source, adding client-side caching, and making unit tests easier to implement. Example shows constructor injection.
   PeopleViewer.Presentation/PeopleViewModel
   PeopleViewer/MainWindow.xaml.cs
   PeopleViewer/App.xaml.cs

2. Read-only Properties/Fields MainDemo-Basics
   Shows the use of read-only properties and fields (set only on construction).
   PeopleViewer.Presentation/PeopleViewModel
   PeopleViewer/MainWindow.xaml.cs

3. Guard Clauses MainDemo-Basics
   Setting up guard clauses to make sure that proper values are provided for constructor parameters.
   PeopleViewer.Presentation/PeopleViewModel
   PeopleViewer/MainWindow.xaml.cs

4. Constructor Injection MainDemo-Basics
   Review of constructor injection (from #1).
   PeopleViewer.Presentation/PeopleViewModel
   PeopleViewer/MainWindow.xaml.cs
   PeopleViewer/App.xaml.cs

5. Property Injection MainDemo-Basics
   Using property injection to have a good default value that can be swapped out for easier unit testing.
   PeopleViewer.CSV/CSVReader.cs
   PersonReader.CSV.Tests

6. Method Injection MethodInjection Using method injection to have potentially different behavior on each call of a method.
   PeopleApplication/App.xaml.cs
   PeopleLibrary

7. Decorators MainDemo-Extended
   A look at adding functionality (such as caching or retry) to existing objects.
   PersonReader.Decorators
   PeopleViewer/App.xaml.cs

8. Static Dependency StaticDependencies
   Dealing with statics by wrapping them in another object that can be injected and controlled for unit testing.
   HouseControl.Library/Schedules/ITimeProvider.cs
   HouseControl.Library/Schedules/CurrentTimeProvider.cs
   HouseControl.Library.Tests

9. Proxy MainDemo-Extended
   Handling IDisposable by wrapping an object in a proxy.
   PersonReader.SQL/SQLReader.cs
   PersonReader.SQL/SQLReaderProxy.cs

10. .NET Core Container MainDemo-Extended
    Looking at the built-in .NET Core dependency injection container.
    PeopleService/Models/HardCodedPeopleProvider.cs
    PeopleService/Controllers/PeopleController.cs
    Startup.cs

11. Ninject (Collection) MethodInjection
    Registering collections of dependencies and resolving them with the Ninject dependency injection container.
    PeopleApplication/App.xaml.cs

12. Ninject (Auto-Registration) MethodInjection
    Using reflection to auto-register types in assemblies with Ninject.
    PeopleApplication/App.xaml.cs

13. Autofac (General) MainDemo-Basics
    Constructor injection using the Autofac dependency injection container. PeopleViewer.Autofac/App.xaml.cs

14. Autofac (Decorator) MainDemo-Basics
    Registering a decorator using Autofac.
    PeopleViewer.Autofac/App.xaml.cs

15. Autofac (Late Binding) MainDemo-Basics
    Using Autofac to load dependencies at runtime based on configuration. This allows for dependencies to be swapped out without recompiling the application.
    PeopleViewer.Autofac.LateBinding/App.xaml.cs
    PeopleViewer.Autofac.LateBinding/autofac.json

16. Configuration Strings MainDemo-Extended
    Handling configuration strings with a container can be tricky. This example shows how we can wrap a string in a custom type to make registering easier (this uses Ninject).
    PersonReader.Service/ServiceReaderUri.cs
    PeopleViewer/App.xaml.cs

Additional Resources

Links to articles, videos, and additional code samples:

• DI Why? Getting a Grip on Dependency Injection
• Diving Deeper into Dependency Injection

For more information, visit jeremybytes.com.