C# 6.0 新特性收集

先来看一段Json.Net的代码

public JObject ToJson()
        {
            var result = new JObject();
            result["X"] = X;
            result["Y"] = Y;
            return result;
        }

改进后的代码可以这么写

public JObject ToJson()
        {
            var result = new JObject()
            {
                ["X"] = X,
                ["Y"] = Y
            };
            return result;
        }

最终可以化简成一行代码

public JObject ToJson() => new JObject() { ["X"] = X, ["Y"] = Y };

1. 静态using(static using)

静态using声明允许不使用类名直接调用静态方法

C# 5

using System;

Console.WriteLine("Hello, World!");

usingstatic System.Console;

WriteLine("Hello, World");

2. 表达式方法(Expression-Bodied Methods)

In C# 5
public bool IsSquare(Rectangle rect)
{
return rect.Height == rect.Width;
}
In C# 6
public bool IsSquare(Rectangle rect) => rect.Height == rect.Width;

1. 方法（Methods）

1   public Student Create() => new Student();

等同于：

1   public Student Create()
2   {
3returnnew Student();
4   }

2. 只读属性（read only properties）

1   publicstring FullName => string.Format("{0},{1}", FirstName, LastName);

等同于：

1   publicstring FullName
2   {
3get4       {
5returnstring.Format("{0},{1}", FirstName, LastName);
6       }
7   }

原理解析：上面的表达式在编译后会生成最原始的方法体和访问器，值得一提的是函数表达式体跟Lambda是两个相似但不相同的东西，函数的表

达式体只能带一句话且不能包含return关键字但Lambda 能带语句块和包含关键字。

public Point Move(int dx, int dy) => new Point(x + dx, y + dy);

再来举一个简单的例子：一个没有返回值的函数

publicvoid Print() => Console.WriteLine(FirstName + " " + LastName);

3. 表达式属性(Expression-Bodied Properties)

跟表达式方法类似，只有一个get访问器的单行属性可以使用lambda语法写。

publicstring FullName { get { return FirstName +"" + LastName; } }

publicstring FullName => FirstName +"" + LastName;

用C#6的这个新特性，代码就会大大减小，而且可读性比起之前大大增强

4. 自动属性初始化器(Auto-Implemented Property Intializers)

In C# 5

publicclassPerson
{
    publicPerson()
    {
        Age = 24;
    }
    publicint Age {get; set;}
}

In C# 6

publicclassPerson
{
    publicint Age {get; set;} = 42;
}

5. 只读自动属性(Read-Only Auto Properties)

In C# 5

privatereadonlyint _bookId;
public BookId
{
    get
    {
        return _bookId;
    }
}

In C# 6

publicBookId {get;}

6. nameof操作符(nameof Operator)

字段、属性、方法和类型的name可以通过nameof访问。使用nameof，可以方便的重构name变化。

In C# 5

publicvoidMethod(object o)
{
    if (o == null) thrownew ArgumentNullException("o");

In C# 6

publicvoidMethod(object o)
{
    if (o == null) thrownew ArgumentNullException(nameof(o));

public class MyClass
{
[TestMethod]
public static void Show(int age)
{
Console.WriteLine(nameof(MyClass)); // 输出 MyClass 类名
Console.WriteLine(nameof(Show)); // 输出 Show 方法名
Console.WriteLine(nameof(age)); // 输出 age
Console.WriteLine(nameof(TestMethodAttribute)) // 输出 Attribute 名
}
}

7. Null传递操作符(Null Propagation Operator)

int? age = p == null ? null : p.Age;

var handler = Event;
if (handler != null)
{
    handler(source, e);
}

In C# 6

int? age = p?.Age;

handler?.Invoke(source, e);

8. 字符串插值(String Interpolation)

C# 6之前我们拼接字符串时需要这样

var Name = "Jack";

var results = "Hello" + Name;

或者

var Name = "Jack";

var results = string.Format("Hello {0}", Name);

WriteLine(($"{Name }"))

9. 字典初始化器(Dictionary Initializers)

In C# 5

var dict = new Dictionary<int, string>();
dict.Add(3,"three");
dict.Add(7,"seven");

In C# 6

var dict = new Dictionary<int, string>()
{
    [3] ="three",
    [7] ="seven"
};

10. 异常过滤器(Exception Filters)

In C# 5

try
{
    //etc.
} catch (MyException ex)
{
    if (ex.ErrorCode != 405) throw;
    // etc.
}

In C# 6

try
{
    //etc.
} catch (MyException ex) when (ex.ErrorCode == 405)
{
    // etc.
}

11. 在Catch使用Await(Await in Catch)

bool hasError = false;
string errorMessage = null;
try
{
    //etc.
} catch (MyException ex)
{
    hasError = true;
    errorMessage = ex.Message;
} 
if (hasError)
{
    awaitnew MessageDialog().ShowAsync(errorMessage);
}

In C# 6

try
{
    //etc.
} catch (MyException ex)
{
    awaitnew MessageDialog().ShowAsync(ex.Message);
}