委托，匿名方法，Lambda表达式使用实例

问题描述

排序函数中需要指定升序或降序排列，如果只是简单使用一个Flag进行标记的话，需要在排序函数中使用if else进行判断。

class SimpleSort
{
    public enum SortType
    {
        Ascending,
        Descending
    }

    void BubleSort(int[] items, SortType sortOrder)
    {
        for (i = items.Length - 1; i >= 0; i--)
        {
            for (j = 1; j <= i; j++)
            {
                bool swap = false;  
                switch (sortOrder)
                {
                    case SortType.Ascending :
                        swap = items[j - 1] > items[j];
                        break;
                    case SortType.Descending :
                        swap = items[j - 1] < items[j];
                        break;
                }
                if (swap)
                {
                    temp = items[j - 1];
                    items[j - 1] = items[j];
                    items[j] = temp;
                }
            }
        }
    }
}

使用委托改进排序方法

public delegate bool ComparisonHandler (int first, int second);

class DelegateSample
{
    public static void BubbleSort(int[] items, ComparisonHandler comparisonMethod)
    {
        int i;
        int j;
        int temp;

        if(comparisonMethod == null)
        {
            throw new ArgumentNullException("comparisonMethod");
        }

        if(items==null)
            return;

        for (i = items.Length - 1; i >= 0; i--)
        {
            for (j = 1; j <= i; j++)
            {
                if (comparisonMethod(items[j - 1], items[j]))
                {
                    temp = items[j - 1];
                    items[j - 1] = items[j];
                    items[j] = temp;
                }
            }
        }
    }

    public static bool GreaterThan(int first, int second)
    {
        return first > second;
    }

    static void Main()
    {
        int i;
        int[] items = new int[5];
        for (i=0; i < items.Length; i++)
        {
            Console.Write("Enter an integer: ");
            items[i] = int.Parse(Console.ReadLine());
        }
        BubbleSort(items, GreaterThan);
        for (int i = 0; i < items.Length; i++)
            Console.WriteLine(items[i]);
    }
}

使用委托

class DelegateSort
{
    public static bool GreaterThan(int first, int second)
    {
        return first > second;
    }

    static void Main()
    {
        int i;
        int[] items = new int[5];
        for (i=0; i < items.Length; i++)
        {
            Console.Write("Enter an integer: ");
            items[i] = int.Parse(Console.ReadLine());
        }
        BubbleSort(items, GreaterThan);
        for (int i = 0; i < items.Length; i++)
            Console.WriteLine(items[i]);
    }
}

匿名方法

BubbleSort(items,
    delegate(int first, int second) => { return first > second; }
);

Lambda表达式

BubbleSort(items,
    (int first, int second) => { return first > second; }
);

BubbleSort(items, (first, second) => first > second);

参考

1.《C#本质论 第六版》