c#3.0新特性
1.自动属性
public int ID { get; set; } // 上面的ID属性（自动属性）等同于下面的ID属性 // private int _id; // public int ID // { // get { return _id; } // set { _id = value; } // }
2.对象初始化器
/// <summary> /// ObjectInitializers（对象初始化器）的摘要说明 /// </summary> public class ObjectInitializers { public int ID { get; set; } public string Name { get; set; } public void ObjectInitializersTest() { ObjectInitializers oi = new ObjectInitializers { ID = 1, Name = "webabcd" }; // 上面的oi对象（对象初始化器）等同于下面的oi对象 // ObjectInitializers oi = new ObjectInitializers(); // oi.ID = 1; // oi.Name = "webabcd"; } }
3.集合初始化器
/// <summary> /// CollectionInitializers（集合初始化器）的摘要说明 /// </summary> public class CollectionInitializers { public int ID { get; set; } public string Name { get; set; } public void CollectionInitializersTest() { List<CollectionInitializers> list = new List<CollectionInitializers> { new CollectionInitializers { ID = 1, Name = "webabcd" }, new CollectionInitializers { ID = 2, Name = "webabcdefg" }, new CollectionInitializers { ID = 3, Name = "webabcdefghijklmn" } }; // 上面的list集合（集合初始化器）等同于下面的list集合 // List<CollectionInitializers> list = new List<CollectionInitializers>(); // list.Add(new CollectionInitializers { ID = 1, Name = "webabcd" }); // list.Add(new CollectionInitializers { ID = 2, Name = "webabcdefg" }); // list.Add(new CollectionInitializers { ID = 3, Name = "webabcdefghijklmn" }); } }
4.扩展方法
/// <summary> /// 扩展方法（类和方法均为static） /// 使用的时候要引用该类的命名空间 /// </summary> public static class MyExtensionMethods { // this代表扩展方法应用于string类型上 // ToInt32()是将string类型转换为int类型的扩展方法 public static int ToInt32(this string s) { int i; Int32.TryParse(s, out i); return i; } // this代表扩展方法应用于object类型上 // 该扩展方法需要一个类型为System.Collections.IEnumerable的参数 // In()是判断一个object是否存在于一个System.Collections.IEnumerable中的扩展方法 public static bool In(this object o, System.Collections.IEnumerable e) { foreach (object i in e) { if (i.Equals(o)) { return true; } } return false; } }
string s = "123"; // 使用string的ToInt32()扩展方法 int i = s.ToInt32(); // i == 123 string[] ary = new string[] { "a", "b", "c" }; // 使用object的In()扩展方法 bool b = "b".In(ary); // b == true
5.Lambda表达式
/// <summary> /// LambdaExpressions（Lambda表达式）的摘要说明 /// </summary> public class LambdaExpressions { public int ID { get; set; } public string Name { get; set; } public void LambdaExpressionsTest() { List<LambdaExpressions> list = new List<LambdaExpressions> { new LambdaExpressions { ID = 1, Name = "webabcd" }, new LambdaExpressions { ID = 2, Name = "webabcdefg" }, new LambdaExpressions { ID = 3, Name = "webabcdefghijklmn" } }; IEnumerable<LambdaExpressions> l = list.Where(le => le.Name == "webabcd"); // 上面的（Lambda表达式）等同于下面的（匿名方法） // IEnumerable<LambdaExpressions> l2 = list.Where(delegate(LambdaExpressions le) { return le.Name == "webabcd"; }); // 相关委托 // public delegate TResult Func<T, TResult>(T arg); // 相关Where扩展方法 // Func<TSource, bool>：接受一个类型为TSource的参数 // Func<TSource, bool>：某个需要满足的条件，返回bool值 // public static IEnumerable<TSource> Where<TSource>(this IEnumerable<TSource> source, Func<TSource, bool> predicate) // { // foreach (TSource item in source) // { // if (predicate(item)) // { // yield return item; // } // } // } } }
6.查询语法
/// <summary> /// QuerySyntax（查询语法）的摘要说明 /// </summary> public class QuerySyntax { public int ID { get; set; } public string Name { get; set; } public void QuerySyntaxTest() { List<QuerySyntax> list = new List<QuerySyntax> { new QuerySyntax { ID = 1, Name = "webabcd" }, new QuerySyntax { ID = 2, Name = "webabcde" }, new QuerySyntax { ID = 2, Name = "webabcdef" }, new QuerySyntax { ID = 2, Name = "webabcdefg" }, new QuerySyntax { ID = 2, Name = "webabcdefgh" }, new QuerySyntax { ID = 2, Name = "webabcdefghi" }, new QuerySyntax { ID = 2, Name = "webabcdefghij" }, new QuerySyntax { ID = 2, Name = "webabcdefghijk" }, new QuerySyntax { ID = 2, Name = "webabcdefghijkl" }, new QuerySyntax { ID = 2, Name = "webabcdefghijklm" }, new QuerySyntax { ID = 3, Name = "webabcdefghijklmn" } }; IEnumerable<QuerySyntax> l = from o in list where o.Name.Length > 10 orderby o.Name.Length descending select o; // 上面的（查询语法）等同于下面的（LINQ扩展方法和Lambda表达式） // 查询语法相对更容易理解 // IEnumerable<QuerySyntax> l = list.Where(o => o.Name.Length > 10).OrderByDescending(o => o.Name.Length); // Projection（映射） // 可以返回一个新的类型 IEnumerable<Projection> l2 = from o in list where o.Name.Length > 10 orderby o.Name.Length descending select new Projection { Name = o.Name }; var l3 = from o in list where o.Name.Length > 10 orderby o.Name.Length descending select new { Name=o.Name}; } } /// <summary> /// 为了演示Projection（映射）而写的实体类 /// </summary> public class Projection { public string Name { get; set; } }
7.匿名对象
/// <summary> /// AnonymousTypes（匿名类型）的摘要说明 /// </summary> public class AnonymousTypes { public int ID { get; set; } public string Name { get; set; } public int Age { get; set; } public void AnonymousTypesTest() { List<AnonymousTypes> list = new List<AnonymousTypes> { new AnonymousTypes { ID = 1, Name = "webabcd", Age = 10 }, new AnonymousTypes { ID = 2, Name = "webabcdefg", Age = 20 }, new AnonymousTypes { ID = 3, Name = "webabcdefghijklmn", Age = 30 } }; // listAnonymousTypes - 匿名类型 var listAnonymousTypes = from l in list where l.Name == "webabcd" select new { Name = l.Name, Age = l.Age }; foreach (var v in listAnonymousTypes) { // v - 匿名类型，可以在Visual Studio中得到编译时检查和完整的intellisense string name = v.Name; int age = v.Age; } // 声明匿名类型：将new关键词后面的类型名称省略掉 var person = new { Name = "webabcd", Age = 27 }; // person - 匿名类型，可以在Visual Studio中得到编译时检查和完整的intellisense string myName = person.Name; int myAge = person.Age; } }
