设计模式（8）组合模式

模式介绍

组合模式使得用户对单个对象和组合对象的使用具有一致性。

示例

我们使用一个汽水售卖机进行建模，这玩意会先让你选择品牌（可乐、芬达、雪碧），然后让你选择口味（樱桃味、香草味）。

定义饮料类

/// <summary>
/// Component abstract class
/// </summary>
public abstract class SoftDrink
{
    public int Calories { get; set; }

    public List<SoftDrink> Flavors { get; set; }

    public SoftDrink(int calories)
    {
        Calories = calories;
        Flavors = new List<SoftDrink>();
    }

    /// <summary>
    /// "Flatten" method, returns all available flavors
    /// </summary>
    public void DisplayCalories()
    {
        Console.WriteLine(this.GetType().Name + ": " + this.Calories.ToString() + " calories.");
        foreach (var drink in this.Flavors)
        {
            drink.DisplayCalories();
        }
    }
}

创建不同口味的不同饮料，可乐（2）、生啤（2）、柠檬汁（1）

/// <summary>
/// Leaf class
/// </summary>
public class VanillaCola : SoftDrink
{
    public VanillaCola(int calories) : base(calories) { }
}

/// <summary>
/// Leaf class
/// </summary>
public class CherryCola : SoftDrink
{
    public CherryCola(int calories) : base(calories) { }
}

/// <summary>
/// Leaf class
/// </summary>
public class StrawberryRootBeer : SoftDrink
{
    public StrawberryRootBeer(int calories) : base(calories) { }
}

/// <summary>
/// Leaf class
/// </summary>
public class VanillaRootBeer : SoftDrink
{
    public VanillaRootBeer(int calories) : base(calories) { }
}

/// <summary>
/// Leaf class
/// </summary>
public class LemonLime : SoftDrink
{
    public LemonLime(int calories) : base(calories) { }
}

组合类

/// <summary>
/// Composite class
/// </summary>
public class Cola : SoftDrink
{
    public Cola(int calories) : base(calories) { }
}

/// <summary>
/// Composite class
/// </summary>
public class RootBeer : SoftDrink
{
    public RootBeer(int calories) : base(calories) { }
}

组合类，根节点

/// <summary>
/// Composite class, root node
/// </summary>
public class SodaWater : SoftDrink
{
    public SodaWater(int calories) : base(calories) { }
}

客户端调用：

static void Main(string[] args)
{
    var colas = new Cola(210);
    colas.Flavors.Add(new VanillaCola(215));
    colas.Flavors.Add(new CherryCola(210));

    var lemonLime = new LemonLime(185);

    var rootBeers = new RootBeer(195);
    rootBeers.Flavors.Add(new VanillaRootBeer(200));
    rootBeers.Flavors.Add(new StrawberryRootBeer(200));

    SodaWater sodaWater = new SodaWater(180);
    sodaWater.Flavors.Add(colas);
    sodaWater.Flavors.Add(lemonLime);
    sodaWater.Flavors.Add(rootBeers);

    sodaWater.DisplayCalories();

    Console.ReadKey();
}

总结

组合模式可以“扁平化”所有或部分层次结构

源代码

https://github.com/exceptionnotfound/DesignPatterns/tree/master/Composite

原文

https://www.exceptionnotfound.net/composite-the-daily-design-pattern/