Favoring Composition over Inheritance

You may have heard the expression before "Favor Composition over Inheritance", but do you know what it means and how to apply it? Lets take this code for example:

abstract class Car
{
	public Color Color { get; protected set; }
	public Engine Engine { get; protected set; }
}

class ElectricCar : Car
{
	public ElectricCar()
	{
		this.Color = Color.Blue;
		this.Engine = new ElectricEngine();
	}
}

class SportsCar : Car
{
	public SportsCar()
	{
		this.Color = Color.Red;
		this.Engine = new V8Engine();
	}
}

class Truck : Car
{
	public Truck()
	{
		this.Color = Color.White;
		this.Engine = new DieselEngine();
	}
}

In this contrived example, we've defined three types of cars. Each instance of each of the cars will always have the same color and same engine. What happens when we need a 4th type? We have to define another class. By refactoring this code, we can compose a car type by giving it a color and an engine:

class Car
{
	public Color Color { get; private set; }
	public Engine Engine { get; private set; }
	
	public Car(Color color, Engine engine)
	{
		this.Color = color;
		this.Engine = engine;
	}
}

Car electricCar = new Car(Color.Blue, new ElectricEngine());
Car sportsCar = new Car(Color.Red, new V8Engine());
Car truck = new Car(Color.White, new DieselEngine());
Car familyCar = new Car(Color.Black, new V4Engine());

Now we can compose many car types, with any combination of colors and engines and we've only defined one class.

Component Glue

The other day I started an open source project for an IoC Container I call Component Glue. It's in a toy / learning tool status right now and I don't know how far I actually want to take the project. More to come though.

Component Glue on Codeplex

Visual Studio - Move referenced DLL to different directory after Build

July 20, 2010 .net msbuild

If you need to move a referenced DLL to a different directory after build, add these commands to the "Post Build event command line" box in the "Build Events" tab of the project properties:

mkdir $(TargetDir)dir
move $(TargetDir)myDLL.dll $(TargetDir)dir\myDLL.dll

Xna: Load Texture2D from Embedded Resource

If you're writing an app which uses Xna, you may need to load a texture from an embedded resource. Here's how:

First embed the resource in your app. Do so by choosing Embedded Resource as the Build Action in the properties of the resource.

After that you can load the Texture2D using a stream handle to the embedded file.

Stream stream = Assembly.GetCallingAssembly().GetManifestResourceStream("AppNamespace.Folder.font.bmp");
return Texture2D.FromFile(graphicsDevice, stream);

GetCallingAssembly() can be exchanged with GetExecutingAssembly() if needed. The name of the resource must be fully qualified with the app's namespace and folders. I usually keep my resources in a folder Resources so I would have: AppNamespace.Resources.font.bmp.

Implementing basic Dependency Injection using a Service Container

By extending your Service Container class, a very basic version of dependency injection can be implemented. We'll implement two forms of dependency injection: constructor and property injection.

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