The Flyweight Design Pattern allows you to share instances of the same object across multiple calls.

In the example on this post I will be reusing a rectangle with the same color, that makes the color property “intrinsic”. But I will not share position and size across the instances, so those characteristics are “extrinsic”.

  1. namespace ConsoleApplication1
  2. {
  3. class Program
  4. {
  5. static void Main(string[] args)
  6. {
  7. var r = FlyweightFactory.Create("Red");
  8. var g = FlyweightFactory.Create("Green");
  9. var b = FlyweightFactory.Create("Blue");
  11. r.Draw(0, 0, 10, 10);
  12. r.Draw(0, 0, 20, 30);
  14. g.Draw(0, 0, 20, 30);
  15. FlyweightFactory.Create("Green").Draw(10, 20, 50, 70);
  17. b.Draw(0, 0, 20, 30);
  19. FlyweightFactory.Create("Purple").Draw(10, 20, 50, 70);
  21. Console.ReadKey(true);
  22. }
  23. }
  25. public class FlyweightFactory
  26. {
  27. private static ConcurrentDictionary<string, Rectangle> cache
  28. = new ConcurrentDictionary<string, Rectangle>();
  30. public static Rectangle Create(string key)
  31. {
  32. return cache.GetOrAdd(key, new Rectangle(key));
  33. }
  34. }
  36. public class Rectangle
  37. {
  38. public Guid ID { get; set; }
  40. public string ColorName { get; set; }
  42. public Rectangle(string name)
  43. {
  44. ID = Guid.NewGuid();
  45. ColorName = name;
  46. }
  48. public void Draw(int x, int y, int width, int height)
  49. {
  50. Console.WriteLine("Rectangle ({0}) instance: {1}"
  51. , ColorName, ID);
  52. Console.WriteLine("X: {0} Y: {1} W: {2} H: {3}"
  53. , x, y, width, height);
  54. Console.WriteLine();
  55. }
  56. }
  57. }

Output:

Flyweight

In a real world example: You could use it in game development. Imagine that you have a system to change a character’s clothes, you don’t need to create an instance of the character itself entirely, having to load expensive resources every time. You could just use a shared instance of the character’s model and have the clothes as the extrinsic part. (And hey, you could have another Flyweight system to reuse clothes instances as well).