一、C#发展历程
下图是自己整理列出了C#每次重要更新的时间及增加的新特性,对于了解C#这些年的发展历程,对C#的认识更加全面,是有帮助的。
二、C#6.0新特性
1、字符串插值 (String Interpolation)
字符串拼接优化
Before:
var Name = "joye.net";
var Results = "Hello" + Name;//直接拼接
var results1 = string.Format("Hello {0}", Name);//Format拼接
After:
var results2 = $"Hello {Name}"; //$拼接
var results= $"Hello {Name}{new Program().GetCnblogsSite()}";//{}可以直接插入代码
2、null检查运算符【 ?.】 (Monadic null checking)
null优化
Before:
public static string GetCnblogsSite()
{
return "http://www.cnblogs.com/yinrq";
}
Program pro = null;
if(pro!=null)
Console.WriteLine(GetCnblogsSite());
After:
Program pro = null;
Console.WriteLine(pro?.GetCnblogsSite());
3、 自动属性初始化器(Initializers for auto-properties)
可以直接给自动属性赋值了,不需要写在构造函数中。
Before:
public class ClassA
{
private string Name{get;set;};
public ClassA()
{
Name = "joye.net";
}
}
After:
public class ClassA
{
public string Name { get; set; } ="joye.net"; }
4、只读自动属性(Getter-only auto-properties)
只读自动属性可以直接初始化,或者在构造函数中初始化。
before
//缩小自动属性的访问权限
public class ClassA
{
public string Name { get; private set; } }
//C#1.0实现
public class ClassA
{
private string Name = "joye.net"; public string Name
{
get { return Name; }
}
}
after:
public class ClassA
{
public string Name { get; } = "joye.net";
}
5、表达式方法体(Property Expressions && Method Expressions)
只读属性,只读索引器和方法都可以使用Lambda表达式作为Body。
一句话的方法体可以直接写成箭头函数,而不再需要大括号(分页控件http://www.cnblogs.com/yinrq/p/5586841.html就用到了属性表达式Property Expressions)
public class PagerInBase
{
/// <summary>
/// 当前页
/// </summary>
public int PageIndex { get; set; } /// <summary>
/// 页数
/// </summary>
public int PageSize { get; set; }
//以前的写法
//public int Skip{get{return (PageIndex - 1) * PageSize}}
//跳过序列中指定数量的元素
public int Skip => (PageIndex - ) * PageSize; /// <summary>
/// 请求URL
/// </summary>
public string RequetUrl => System.Web.HttpContext.Current.Request.Url.OriginalString; /// <summary>
/// 构造函数给当前页和页数初始化
/// </summary>
public PagerInBase()
{
if (PageIndex == ) PageIndex = ;
if (PageSize == ) PageSize = ;
}
}
方法表达式(Method Expressions)
//before 的完整方法
public int Skip()
{
return (PageIndex - ) * PageSize
}
//After C#6.0 方法表达式
public int Skip() => (PageIndex - ) * PageSize;
6、using静态类(Static type using statements)
using System;
using static System.Math;
namespace ConsoleApplication1
{
class Program
{
static void Main(string[] args)
{
Console.WriteLine(Log10() + PI);
}
}
}
7、检查方法参数nameof表达式(nameof expressions)
这个很有用,原来写WPF中的ViewModel层的属性变化通知时,需要写字符串,或者使用MvvmLight等库中的帮助方法,可以直接传入属性,但由于是在运行时解析,会有少许性能损失。现在使用nameof运算符,保证重构安全和可读性,又提升了性能。
Before:
public static void Add(Person person)
{
if (person == null)
{
throw new ArgumentNullException("person");
}
}
After:
public static void Add(Person person)
{
if (person == null)
{
throw new ArgumentNullException(nameof(person));
}
}
8、带索引的对象初始化器(Index initializers )
直接通过索引进行对象的初始化
var dic = new Dictionary<int, string> { []="joye.net",[]= "http://yinrq.cnblogs.com/",[]= "Index initializers " };
9、catch和finally 中使用await (catch和finally 中的 await )
在C#5.0中,await关键字是不能出现在catch和finnaly块中的。而C#6.0可以
try
{
res = await Resource.OpenAsync(…); // You could do this
}
catch (ResourceException e)
{
await Resource.LogAsync(res, e); // Now you can do this
}
finally
{
if (res != null)
await res.CloseAsync(); // finally and do this.
}
10、内联out参数(Inline declarations for out params)
before
int x;
int.TryParse("", out x);
after:
int.TryParse("", out int x);
11、无参数的结构体构造函数(Parameterless constructors in structs)
public struct MyStruct
{
public int A { get; }
public int B { get; }
public MyStruct(int a, int b) { A = a; B = b; }
public MyStruct(): this(, ) { } }
WriteLine(new MyStruct().ToString());
WriteLine(default(MyStruct).ToString());
三、代码
using System;
using System.Collections.Generic;
using static System.Console; namespace ConsoleApplication1
{
public class MyClass
{
public int A { get; set; } public int B { get; set; } = ; public string Separator { get; } = "/"; public string SeparatorSpaces { get; } = string.Empty; public double Value => (double)A / B; public int this[int index] => index == ? A : B; public int this[string index] => index == "A" ? A : B; public override string ToString() => "{A}{SeparatorSpaces}{Separator}{SeparatorSpaces}{B}"; public void Print() => WriteLine(ToString()); public MyClass()
{ } public MyClass(int a, int b)
{
A = a;
B = b;
} public MyClass(int a, int b, string separatorSpaces) : this(a, b)
{
SeparatorSpaces = separatorSpaces;
if (string.IsNullOrEmpty(separatorSpaces))
{
throw new ArgumentNullException(nameof(separatorSpaces));
}
} public static readonly Dictionary<string, MyClass> Dic =
new Dictionary<string, MyClass>
{
["zero"] = new MyClass(),
["one"] = new MyClass(, ),
["half"] = new MyClass(, ),
["quarter"] = new MyClass(, ),
["infinity"] = new MyClass(, ),
}; } public struct MyStruct
{
public int A { get; }
public int B { get; }
public MyStruct(int a, int b) { A = a; B = b; }
public MyStruct(): this(, ) { } public override string ToString() => "{A}{B}"; } class Program
{
static void Main(string[] args)
{
foreach (var f in MyClass.Dic)
{
WriteLine("{f.Key} : {f.Value.Value}");
} var fraction = new MyClass(, , " ");
fraction.Print(); try
{
fraction = new MyClass(, , null);
}
catch (ArgumentNullException e)
{
if (e.ParamName == "separatorSpaces")
WriteLine("separatorSpaces can not be null");
} MyClass v;
MyClass.Dic.TryGetValue("harf", out v);
v?.Print();
var a = v?.A;
WriteLine(a == null);
var b = v?["B"];
WriteLine(b == null);
WriteLine(v?.ToString() == null); WriteLine(new MyStruct().ToString());
WriteLine(default(MyStruct).ToString());
} }
}