享元模式

定义

当系统中需要多次创建某些对象，而这些对象又无需改变，或者是改变时均一致时。可以只创建对应类的对象，并将其存于内存中，实现共享，需要用到时直接内存获取，无需多次创建。

类图

代码

  public abstract class BaseColor
    {
        private string name;
        public BaseColor(string colorName)
        {
            name = colorName;
        }
        public virtual int GetValue()
        {
            return 0x000FFF;
        }
    }
    public class RedColor : BaseColor
    {
        public RedColor() : base("RedColor")
        {

        }
        public override int GetValue()
        {
            return 0xFFC0CB;
        }
    }
    public class BlueColor : BaseColor
    {
        public BlueColor() : base("BlueColor")
        {

        }
        public override int GetValue()
        {
            return 0x0000FF;
        }
    }
    public class ColorFlyweightFactory
    {
        private Dictionary<string, BaseColor> colors;
        private static object mLock = new object();
        private static ColorFlyweightFactory instance = null;
        private ColorFlyweightFactory()
        {
            colors = new Dictionary<string, BaseColor>();
        }
        public static ColorFlyweightFactory GetInstance()
        {
            if (instance == null)
            {
                lock (mLock)
                {
                    if (instance == null)
                    {
                        instance = new ColorFlyweightFactory();
                    }
                }
            }
            return instance;
        }
        /// <summary>
        /// 创建颜色
        /// </summary>
        /// <param name="colorName">约定使用颜色类名作为参数</param>
        /// <returns></returns>
        public BaseColor CreateColor(string colorName)
        {
            if (colors.ContainsKey(colorName))
            {
                return colors[colorName];
            }
            else
            {
                try
                {
                    //约定使用颜色类名作为参数，当然可以分离出去，此处略
                    BaseColor color = (BaseColor)Activator.CreateInstance(Type.GetType(colorName));
                    colors.Add(colorName, color);
                    return color;
                }
                catch (Exception ex)
                {
                    throw new Exception(string.Format("不存在{0}", colorName),ex);
                }
            }
        }
    }
    public class ColorClient
    {
        BaseColor red= ColorFlyweightFactory.GetInstance().CreateColor("RedColor");
        BaseColor blue = ColorFlyweightFactory.GetInstance().CreateColor("BlueColor");
        BaseColor red2 = ColorFlyweightFactory.GetInstance().CreateColor("RedColor");//当再次需要到红色时，无需再创建，直接从工厂的字典中获取
        BaseColor blue2 = ColorFlyweightFactory.GetInstance().CreateColor("BlueColor");//再次需要蓝色也无需再次创建。
    }

总结

享元模式在于确定了类对象具有同步可共用的特征，通过缓存管理，减少对象创建和销毁的性能消耗，代码和对象均可实现良好的管理。