[AttributeUsage(AttributeTargets.Class), AllowMultiple=true]
sealed class DecoratorAttribute : Attribute
{
    public readonly object Injector;
    private Type type;
 
    public DecoratorAttribute(Type type)
    {
        if (type == null) throw new ArgumentNullException("type");
        this.type = type;
        Injector = (new Assembler()).Create(this.type);
    }
 
    public Type Type { get { return this.type; } }
}
 
static class AttributeHelper
{
    public static T Injector(object target)//[color=#FF0000]这个泛型怎么解释我不太懂[/color]
        where T : class
    {
        if (target == null) throw new ArgumentNullException("target");
        Type targetType = target.GetType();
        object[] attributes = targetType.GetCustomAttributes(
            typeof(DecoratorAttribute), false);
        if ((attributes == null) || (attributes.Length <= 0)) return null;
        foreach (DecoratorAttribute attribute in
            (DecoratorAttribute [])attributes)
            if (attribute.Type == typeof(T))// if (attribute.Type.GetInterfaces().Contains(typeof(T)))
                return (T)attribute.Injector;
        return null;
    }
}
 
[Decorator(typeof(ITimeProvider)]//[color=#FF0000]这里应该使用可实例化的类吧，不应该使用接口吧[/color]
class Client
{
    public int GetYear()
    {
        ITimeProvider provider =
            AttributeHelper.Injector(this);
        return provider.CurrentDate.Year;
    }
}