Delegate,AnonymousDelegate,Func,LambdaExpression,Linq演化過程程式範例

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace TestLambdaExpression2
{
  static class Program
  {
    static void Main(string[] args)
    {
      List allPerson = GetAllPerson();

      #region Func
      //1.
      Func FuncSelector = new Func(heightselector);
      Console.WriteLine(GetMaxFunc(allPerson, FuncSelector));

      //2.
      Func FuncSelector2 = heightselector;
      Console.WriteLine(GetMaxFunc(allPerson, FuncSelector2));

      //3.
      Console.WriteLine(GetMaxFunc(allPerson, heightselector)); 

      //4.
      Console.WriteLine(allPerson.GetMaxFunc(heightselector));

      //5.使用Lambda Expressions精簡Func之寫作
      Console.WriteLine(allPerson.GetMaxFunc(p => p.height));

      //6.因為Max為多型,必須先宣告形式才不會發生錯誤
      Func FuncSelector3 = heightselector;
      Console.WriteLine(allPerson.Max(FuncSelector3));
      #endregion


      #region Delegate
      //1.
      heightestSelector DelegateSelector = heightselector;
      Console.WriteLine(GetMaxDelegate(allPerson, DelegateSelector));

      //2.
      Console.WriteLine(GetMaxDelegate(allPerson, heightselector));

      //3.
      Console.WriteLine(allPerson.GetMaxDelegate(heightselector));

      //4.AnonymousDelegate
      Console.WriteLine(allPerson.GetMaxDelegate(delegate(Person p) { return p.height; }));

      //5.使用Lambda Expressions精簡AnonymousDelegate之寫作
      Console.WriteLine(allPerson.GetMaxDelegate(p => p.height));

      //6.會發生錯誤,因System.linq.Max需定義Func..不可傳入Delegate,會無法判定型式
      //heightestSelector DelegateSelector2 = heightselector;
      //Console.WriteLine(allPerson.Max(DelegateSelector2));

      //7.使用System.linq.Max,AnonymousDelegate
      Console.WriteLine(allPerson.Max(delegate(Person p) { return p.height; }));

      //8.使用System.linq.Max,Lambda Expressions精簡AnonymousDelegate之寫作
      Console.WriteLine(allPerson.Max(p => p.height));

      Man[] mans = Array.ConvertAll(allPerson.ToArray(), p => new Man() { name = p.name, weight = p.weight });
      Console.WriteLine(mans.Max(p => p.weight));
      #endregion

    }

    public delegate int heightestSelector(Person p);

    public static int heightselector(Person p) { return p.height; }

    private static int GetMaxFunc(this List allPerson, Func selector)
    {
      return (from i in allPerson
              select selector(i)).Max();
    }

    //private static decimal GetMaxFunc(this List allPerson, Func selector)
    //{
    //  return (from i in allPerson
    //          select selector(i)).Max();
    //}

    private static int GetMaxDelegate(this List allPerson, heightestSelector selector)
    {
      return (from i in allPerson
              select selector(i)).Max();
    }

    static List GetAllPerson()
    {
      List persons = new List();
      persons.Add(new Person { name = "A", height = 150, weight = 50 });
      persons.Add(new Person { name = "B", height = 160, weight = 60 });
      persons.Add(new Person { name = "C", height = 170, weight = 70 });
      persons.Add(new Person { name = "D", height = 180, weight = 80 });
      persons.Add(new Person { name = "E", height = 190, weight = 90 });
      return persons;
    }
  }

  public class Person
  {
    public string name { get; set; }
    public int height { get; set; }
    public int weight { get; set; }
  }

  public class Man
  {
    public string name { get; set; }
    public int weight { get; set; }
  }
}

LINQ強大威力

今天下午花了些時間研究 LINQ，這果然是殺手級的東西啊！ 光是去 http://www.asp.net/learn/linq-videos/ 這裡看了四個影片，就覺得真是不可思議的強，LINQ to SQL 真是好東西，解決了許多之前 Typed DataSet 做不到的事，又將整個資料庫操作的過程徹底的物件化與簡化，跟 SQL Server 的整合又更完整了。 大家有興趣可以去看看影片，沒幾分鐘： http://www.asp.net/learn/linq-videos/ 底下是在 Scott Guthrie 網站的文章，寫得很清楚且圖文並茂，看完影片可以來這裡建立更完整的觀念： Part 1: Introduction to LINQ to SQL Part 2: Defining our Data Model Classes Part 3: Querying our Database Part 4: Updating our Database Part 5: Binding UI using the ASP:LinqDataSource Control Part 6: Retrieving Data Using Stored Procedures Part 7: Updating our Database using Stored Procedures Part 8: Executing Custom SQL Expressions Part 9 - Using a Custom LINQ Expression with the control