Design Pattern : Mediator

Design Pattern : Mediator

Definition :

「Define an object that encapsulates how a set of objects interact. Mediator promotes loose coupling by keeping objects from referring to each other explicitly, and it lets you vary their interaction independently.」

 

IMediator : 存放多個要處理的IColleague物件，並定義這些IColleague物件交流、溝通的方法。

IColleague： 必須知道對應的IMediator是誰。 另外裡面也可定義各自溝通方法的細節。

底下的範例是透過Mediator的架構，將三種不同型別的車子物件互相轉換（ICar, ICarMidRange, ICarEliteRange）。 定義好車子後，將車子放入各自的ConcreteColleague物件及定義轉換方法，Clinet存取時只要由Mediator去做轉換即可。

1.  IColleague:

public interface IColleague<T>
{
     /// <summary>
     /// Mediator
     /// </summary>
     IMediator<T> mediator { get;set; }
     /// <summary>
     /// 實際要處理的物件
     /// </summary>
     T obj {get;set;}
}

2.  IMediator:

public interface IMediator<T>
{
    /// IColleague集合
    List<IColleague<T>> ColleagueList { get; }
    /// 加入IColleague物件
    void Register(IColleague<T> colleague);
    /// 轉換方法
    void Transfer(String newTypeName);
}

3.  ConcreteColleague :
=> ToCarMidRange 及 ToCarEliteRange 是轉換的細節方法，故省略之。

public class CarColleague<T> : IColleague<T>
{
    public T obj {get;set;}

    public IMediator<T> mediator { get; set; }

    public CarColleague(IMediator<T> _mediator)
    {
        this.mediator = _mediator;
    }
    public ICarMidRange ToCarMidRange()
    { //Skip the inside codes }
    public ICarEliteRange ToCarEliteRange()
    { //Skip the inside codes }
}

4.  ConcreteMediator:
=> CarMediator 實作了IMediator，重點在於Transfer這個方法中必須確保集合中已有物件，另外轉換的實際的方法是寫在ConcreteClleague裡面，但也可以選擇放在其他類別。

public class CarMediator<T> : IMediator<T>
{
    private List<IColleague<T>> colleagueList = null;
    public CarMediator()
    {
       this.colleagueList = new List<IColleague<T>>();
    }
    public List<IColleague<T>> ColleagueList
    { get { return this.colleagueList; } }
   
    public void Transfer(String newTypeName)
    {
         if (this.colleagueList.Count == 2)
         {
             if (newTypeName == typeof(ICarMidRange).Name)
             {
                object newCar = (this.colleagueList[0] as CarColleague<T>).ToCarMidRange() as object;
                this.colleagueList[1].obj = (T)newCar;
             }
             else if (newTypeName == typeof(ICarEliteRange).Name)
             {
                object newCar = (this.colleagueList[0] as CarColleague<T>).ToCarEliteRange() as object;
                this.colleagueList[1].obj = (T)newCar;
             }
             else {
                throw new Exception("無法轉換，因為尚未定義轉換方法!");
             }
         }
         else { throw new Exception("尚未加入任何Colleague物件!"); }
    }
  
    public void Register(IColleague<T> colleague)
    {
       this.colleagueList.Add(colleague);
    }
}

5.  主程式： 這邊列出從ICar轉換為ICarMidRange的部分…

ICar focus = new Focus();
focus.Color = Color.Blue;
focus.Name = "胖兔二號";
focus.Equipment = "FHD行車紀錄器,倒車雷達";

//Mediator
IMediator<ICar> mediator = new CarMediator<ICar>();

//建立一個要轉換的CarColleague
IColleague<ICar> colleagueBefore = new CarColleague<ICar>(mediator);
colleagueBefore.obj = focus;

//建立一個轉換後的CarColleague
IColleague<ICar> colleagueAfter = new CarColleague<ICar>(mediator);
colleagueAfter.obj = new CarMidRangePrototype();

//註冊Colleague到Mediator
mediator.Register(colleagueBefore);
mediator.Register(colleagueAfter);

mediator.Transfer(typeof(ICarMidRange).Name);

6.  Reference
Mediator Design Pattern