C# 3.0新特性体验之Lambda表达式
【IT168 技术文档】
假设你需要创建一个按钮，当点击它的时候更新ListBox里的内容。在C#1.0和1.1里，你要这样做：
在C#2.0里，你需要这样做：
// Program.cs
using System;
using System.Collections.Generic;
using System.Text;
using System.Query;
using System.XML.XLinq;
using System.Data.DLinq;
namespace LambdaExample
...{
public delegate bool KeyValueFilter<K, V>(K key, V value);
static class Program
...{
static void Main(string[] args)
...{
List<string> list = new List<string>();
list.Add("AA");
list.Add("ABC");
list.Add("DEFG");
list.Add("XYZ");
Console.WriteLine("Through Anonymous method");
AnonMethod(list);
Console.WriteLine("Through Lambda expression");
LambdaExample(list);
Dictionary<string, int> varClothes= new Dictionary<string,int>();
varClothes.Add("Jeans", 20);
varClothes.Add("Shirts", 15);
varClothes.Add("Pajamas", 9);
varClothes.Add("Shoes", 9);
var ClothesListShortage = varClothes.FilterBy((string name,
int count) => name == "Shoes" && count < 10);
// example of multiple parameters
if(ClothesListShortage.Count > 0)
Console.WriteLine("We are short of shoes");
Console.ReadLine();
}
static void AnonMethod(List<string> list)
...{
List<string> evenNumbers = list.FindAll(delegate(string i)
...{ return (i.Length % 2) == 0; });
foreach (string evenNumber in evenNumbers)
...{
Console.WriteLine(evenNumber);
}
}
static void LambdaExample(List<string> list)
...{
var evenNumbers = list.FindAll(i =>(i.Length % 2) == 0);
// example of single parameter
foreach(string i in evenNumbers)
...{
Console.WriteLine(i);
}
}
}
public static class Extensions
...{
public static Dictionary<K, V> FilterBy<K, V>
(this Dictionary<K, V> items, KeyValueFilter<K, V> filter)
...{
var result = new Dictionary<K, V>();
foreach(KeyValuePair<K, V> element in items)
...{
if (filter(element.Key, element.Value))
result.Add(element.Key, element.Value);
}
return result;
}
}
}
如果你安装了Visual Studio 2005 and LinQ Preview，你可以使用编辑器来编译程序。如果没有的话，可以使用命令行方式：
C:\Program Files\LINQ Preview\Bin\Csc.exe /reference:"C:\Program Files\LINQ Preview\Bin\System.Data.DLinq.dll" /reference:C:\Windows\Microsoft.net\Framework\v2.0.50727\System.Data.dll /reference:C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\System.dll /reference:"C:\Program Files\LINQ Preview\Bin\System.Query.dll" /reference:C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\System.XML.dll /reference:"C:\Program Files\LINQ Preview\Bin\System.Xml.XLinq.dll" /target:exe Program.cs
.method private hidebysig static void AnonMethod(class [mscorlib]System.Collections.Generic.List`1<string> list) cil managed { // Code size 96 (0x60) .maxstack 4 .locals init ([0] class [mscorlib]System.Collections.Generic.List `1<string> evenNumbers, [1] string evenNumber, [2] valuetype [mscorlib]System.Collections.Generic.List `1/Enumerator<string> CSCODE_REPLACEMENT 000, [3] bool CSCODE_REPLACEMENT 001) IL_0000: nop IL_0001: ldarg.0 IL_0002: ldsfld class [mscorlib]System.Predicate `1<string> LambdaExample.Program:: `<>9__CachedAnonymousMethodDelegate1' IL_0007: brtrue.s IL_001c IL_0009: ldnull IL_000a: ldftn bool LambdaExample.Program:: `<AnonMethod>b__0'(string) IL_0010: newobj instance void class [mscorlib]System.Predicate `1<string>::.ctor(object, native int) IL_0015: stsfld class [mscorlib]System.Predicate`1<string> LambdaExample.Program:: `<>9__CachedAnonymousMethodDelegate1' IL_001a: br.s IL_001c IL_001c: ldsfld class [mscorlib]System.Predicate`1<string> LambdaExample.Program::'<> 9__CachedAnonymousMethodDelegate1' IL_0021: callvirt instance class [mscorlib]System.Collections. Generic.List`1<!0> class [mscorlib]System. Collections.Generic.List`1<string>:: FindAll(class [mscorlib]System.Predicate`1<!0>) IL_0026: stloc.0 IL_0027: nop IL_0028: ldloc.0 IL_0029: callvirt instance valuetype [mscorlib]System.Collections. Generic.List`1/Enumerator<!0> class [mscorlib]System.Collections.Generic.List`1 <string>::GetEnumerator() IL_002e: stloc.2 .try { IL_002f: br.s IL_0042 IL_0031: ldloca.s CSCODE_REPLACEMENT 000 IL_0033: call instance !0 valuetype [mscorlib]System. Collections.Generic.List`1/Enumerator <string>::get_Current() IL_0038: stloc.1 IL_0039: nop IL_003a: ldloc.1 IL_003b: call void [mscorlib]System.Console:: WriteLine(string) IL_0040: nop IL_0041: nop IL_0042: ldloca.s CSCODE_REPLACEMENT 000 IL_0044: call instance bool valuetype [mscorlib]System. Collections.Generic.List`1/Enumerator <string>::MoveNext() IL_0049: stloc.3 IL_004a: ldloc.3 IL_004b: brtrue.s IL_0031 IL_004d: leave.s IL_005e } // end .try finally { IL_004f: ldloca.s CSCODE_REPLACEMENT 000 IL_0051: constrained. valuetype [mscorlib]System.Collections. Generic.List`1/Enumerator<string> IL_0057: callvirt instance void [mscorlib]System. IDisposable::Dispose() IL_005c: nop IL_005d: endfinally } // end handler IL_005e: nop IL_005f: ret } // end of method Program::AnonMethod
var ClothesListShortage = clothesList.FilterBy((string name, int count) => name == "Shoes" && count < 10);
