C#传值、输出、引用、数组、具名、可选参数,扩展方法

1、值参数声明时不带修饰符的形参是值形参。一个值形参对应一个局部变量，只是它的初 始值来自于该方法调用所提供的相应实参。快速替换变量Alt + Enterusing System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;namespace ParametersExampleclass Programstatic void Main(string args)Student Oldstu = new Student() Name = Tim ;So

2、meMethod(Oldstu);Console.WriteLine(0, 1, Oldstu.GetHashCode(),Oldstu.Name);static void SomeMethod(Student stu)stu = new Student() Name = Tom ;Console.WriteLine(0, 1, stu.GetHashCode(), stu.Name);class Studentpublic string Name get; set; using System;using System.Collections.Generic;using System.Linq

3、;using System.Text;using System.Threading.Tasks;namespace ParametersExampleclass Programstatic void Main(string args)Student stu = new Student() Name = Tim;UpdateObject(stu);Console.WriteLine(0, 1, stu.GetHashCode(), stu.Name);static void UpdateObject(Student stu)stu.Name = Tom;/ 副作用，side-effectCons

4、ole.WriteLine(0, 1, stu.GetHashCode(), stu.Name);class Studentpublic string Name get; set; 引用参数引用形参是用ref修饰符声明的实参，引用形参并不创建新的存储位置。引用形 参表示的存储位置恰是在方法调用中作为实参给出的那个变量所表示的存储位 置。变量在可以作为引用形参之前，必须先明确辅助。注意：引用参数并不创建变量的副本使用ref修饰符显示指出一一此方法的副作用是改变实际参数的值using System;using System.Collections.Generic;using System.Linq

5、;using System.Text;using System.Threading.Tasks;namespace ParametersExample class Program static void 5如 args)int y = 1;IWantSideEffect(ref y);static void IWantSideEffect(ref int x)/x*引用参数-引用类型，创建新对象using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Thread

6、ing.Tasks;namespace ParametersExampleclass Programstatic void Main(string args)Student outterStu = new Student() Name = Tim ;Console.WriteLine(HashCode=0, Name=1, outterStu.GetHashCode(), outterStu.Name);Console.WriteLine();IWantSideEffect(ref outterStu);Console.WriteLine(HashCode=0, Name=1, outterS

7、tu.GetHashCode(), outterStu.Name);static void IWantSideEffect(ref Student stu)stu = new Student() Name = Tom ;Console.WriteLine(HashCode=0, Name=1, stu.GetHashCode(),stu.Name);class Student岫 string g 5引用参数-引用类型，不创建新对象只改变对象值此时与传值参数去掉(ref)在效果上并无不同，但机理不一样；前者的outterStu stu指针一致，后者为指针的指针一致using System;usi

8、ng System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;namespace ParametersExampleclass Programstatic void Main(string args)Student outterStu = new Student() Name = Tim ;Console.WriteLine(HashCode=0, Name=1,outterStu.GetHashCode(), outterStu.Name);Console.Writ

9、eLine();IWantSideEffect(ref outterStu);Console.WriteLine(HashCode=0, Name=1,outterStu.GetHashCode(), outterStu.Name);static void IWantSideEffect(ref Student stu)stu.Name = Tom;Console.WriteLine(HashCode=0, Name=1,stu.GetHashCode(),stu.Name);class Studentpublic string Name get; set; 输出形参用out修饰符声明的形参；

10、输出形参不需要创建新的存储位置；变量在可以作为 输出形参传递之前不一定需要明确赋值；在方法返回之前，该方法的每个输出形 参都必须明确赋值；注意：输出参数并不创建变量的副本方法体内必需要有对输出变量的赋值的操作用Out修饰符显示指出一一此方法的副作用是通过参数向外输出值从语义上讲一一ref是为了 “改变”，out是为了 “输出”输出参数一一值类型using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;namespace Parame

11、tersExampleclass Programstatic void Main(string args)Console.WriteLine(Please inout first number:);string arg1 = Console.ReadLine();double x = 0;bool b1 = double.TryParse(arg1, out x);if(b1 = false)Console.WriteLine(Input error!);return;Console.WriteLine(Please inout second number:);string arg2 = Co

12、nsole.ReadLine();double y = 0;bool b2 = double.TryParse(arg2, out y);if (b2 = false)Console.WriteLine(Input error!);return;double z = x + y;Console.WriteLine(0 + 1 = 2”, x, y, z);using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;namespace

13、ParametersExampleclass Programstatic void Main(string args)f x = 100；bool b = DoubleParser.TryParse(ABC”, out x);:(b=true)_+1);elseerb_ i_tryResult = doub5catch板t=0;/”输出类型一一引用类型using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;namespace Pa

14、rametersExampleclass Programstatic void Main(string args)Student stu = null;bool b = StudentFactory.Create(Tim”, 34, out stu);if (b = true)Console.WriteLine(Student 0, age is 1.”, stu.Name, stu.Age);class Studentpublic int Age get; set; public string Name get; set; class StudentFactorypublic static

15、bool Create(string stuName, int stuAge, out Student result)result = null;if(string.IsNullOrEmpty(stuName)return false;if(stuAge80)return false;_,心5数组参数必需是形参列表中的最后一个，由params修饰举例：String.Format 方法和 String.Split 方法using System;using System.Collections.Generic;using System.Linq;using System.Text;using Sy

16、stem.Threading.Tasks;namespace ParametersExampleclass Programstatic void Main(string args)int result = CalculateSum(1, 2, 3);：_ 5)int sum = 0;一,5广+=-，广；using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;namespace ParametersExample( class Pr

17、ogram1 M void 55,(s.string result = str.Split(;, ., ,);i(n”具名参数参数的位置不再受约束提高代码可读性using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;namespace ParametersExampleclass Program static void gs)P_ );g Prage)enam可选参数参数因为具有默认值而变得“可选”不推荐使用可选参数using S

18、ystem;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;namespace ParametersExampleclass Program static 用 5倾 args)PrinfInfo();static void PrinfInfo(string name = Tim, int age = 34)Ceige)扩展方法(this参数)方法必需是公有的、静态的，即被public static所修饰必需是形参列表中的第一个，由this修饰必需由一个静态类(一般类名为SomeTypeExtension)来统一收纳对SomeType类型的扩展方法举例：LINQ方法using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Task