C# How To系列
1.实例化一个类
using System;
namespace Csharp_how_to
{
class Program
{
static void Main(string[] args)
{
// method 1
Student stu1 = new Student();
stu1.Name = "tom";
stu1.Id = 100;
// method 2
Student stu2 = new Student
{
Name = "jhon",
Id = 99,
};
// method 3
Student stu3 = new Student("james", 101);
Console.WriteLine(stu1.ToString());
Console.WriteLine(stu2.ToString());
Console.WriteLine(stu3.ToString());
Console.ReadKey();
}
}
class Student
{
public string Name { get; set; }
public int Id { get; set; }
// no param constructor
public Student()
{
}
// two param constrcutor
public Student(string name, int id)
{
this.Name = name;
this.Id = id;
}
public override string ToString()
{
return "Name:" + this.Name + "\t" + "Id:" + this.Id;
}
}
}
//Running Result:
//Name:tom Id:100
//Name:jhon Id:99
//Name:james Id:101
2.索引器
using System;
using System.Collections.Generic;
namespace Csharp_how_to
{
class Program
{
static void Main(string[] args)
{
var team = new BaseballTeam
{
["RF"] = "Jhon",
[4] = "Danie",
["CF"] = "Mike",
};
Console.WriteLine(team[4]);
Console.ReadKey();
}
}
public class BaseballTeam
{
private string[] players = new string[9];
private readonly List<string> positionAbbreviations = new List<string>()
{
"p","C","1B","2B","3B","SS","LF","CF","RF"
};
// indexer
public string this[int position]
{
// Baseball positions are 1-9
get { return players[position - 1]; }
set { players[position - 1] = value; }
}
// indexer
public string this[string position]
{
get { return players[positionAbbreviations.IndexOf(position)]; }
set { players[positionAbbreviations.IndexOf(position)] = value; }
}
}
}
3.通过Collection初始化器初始化字典
using System;
using System.Collections.Generic;
using System.Linq;
namespace Csharp_how_to
{
class Program
{
static void Main()
{
var students = new Dictionary<int, StudentName>()
{
{111,new StudentName{FirstName="Sachin",LastName="Karnik",Id=211} },
{112,new StudentName{FirstName="Dina",LastName="Abbas",Id=222} },
{113,new StudentName{FirstName="Jhon",LastName="Mikle",Id=233} }
};
foreach(var index in Enumerable.Range(111,3))
{
Console.WriteLine($"Student{index} is {students[index].FirstName}·{students[index].LastName}");
}
Console.ReadKey();
}
}
class StudentName
{
public string FirstName { get; set; }
public string LastName { get; set; }
public int Id { get; set; }
}
}
4.Partial Class/Method
对于一些比较大的项目，可以把同一个类分给好几个程序员去编码，最后编译的时候编译器会把标名为partial字样的类会合在一起编译吗，与写进一个class 没有区别。下面以StudentName类为例说名
// 这个部分定义两个属性，姓和名
partial class StudentName
{
public string FirstName { get; set; }
public string LastName { get; set; }
}
// 这个部分再定义一个属性Id和构造器
partial class StudentName
{
public int Id { get; set; }
public StudentName(string f,string l,int id)
{
this.FirstName = f;
this.LastName = l;
this.Id = id;
}
public override ToString()
{
return "Name:"+this.FirstName+"·"+this.LastName+"\t"+"Id:"+this.Id;
}
}
public static void Main(string[] args)
{
Student student=new Student("mikle","Jhon",111);
Console.WriteLine(student.ToString())
}
同理，接口也可以分成好几个部分编码，效果同上。以IAnimal接口为例说明
using System;
using System.Collections.Generic;
using System.Linq;
namespace Csharp_how_to
{
public partial interface IAnimal
{
void Eat();
void Run();
}
public partial interface IAnimal
{
void Sleep();
void Shout();
}
public class Animal : IAnimal
{
public void Eat()
{
Console.WriteLine("I am eating");
}
public void Run()
{
Console.WriteLine("I am running");
}
public void Shout()
{
Console.WriteLine("I am shouting");
}
public void Sleep()
{
Console.WriteLine("I am slepping");
}
}
class Program
{
static void Main()
{
Animal animal = new Animal();
animal.Eat();
animal.Run();
animal.Shout();
animal.Sleep();
animal.Sleep();
Console.ReadKey();
}
}
}
同理，方法也可以写成Partial
using System;
using System.Collections.Generic;
using System.Linq;
namespace Csharp_how_to
{
public partial class Animal
{
partial void Sleep();
}
public partial class Animal
{
partial void Sleep()
{
Console.WriteLine("ZZZ~~~");
}
}
}
5.方法传类参数和结构体参数的区别
因为结构体是值类型的，把一个值类型的数值作为方法的参数传入时会复制一份新的给方法，不会拿到最原始的数据地址，所以结构体作为方法参数时不能对其进行修改。
类是引用类型的，一个类作为方法的参数传入时同样会复制一份出来给方法用，同时这个新复制出来的数值也是指向原先数值的地址，即可以根据这个地址去拿到最先的那个变量，所以可以通过传入的参数来对原来的数字进行修改。下面以实例说明：
using System;
namespace ConsoleApp1
{
public class TheClass
{
public string willIChange;
}
public struct TheStrcut
{
public string willIChange;
}
class Program
{
static void classTaker(TheClass c)
{
c.willIChange = "Changed";
}
static void strcutTaker(TheStrcut s)
{
s.willIChange = "Changed";
}
static void Main(string[] args)
{
TheClass testClass = new TheClass();
TheStrcut testStruct = new TheStrcut();
testClass.willIChange = "Not Changed";
testStruct.willIChange = "Not Changed";
classTaker(testClass);
strcutTaker(testStruct);
Console.WriteLine($"Class filed={testClass.willIChange}");
Console.WriteLine($"Struct filed={testStruct.willIChange}");
Console.ReadKey();
}
}
}
6.运算符重载
using System;
namespace ConsoleApp1
{
public readonly struct Fraction
{
public readonly int num;
public readonly int den;
public Fraction(int numerator,int denominator)
{
if(denominator==0)
{
throw new ArgumentException("Denomintor can not be zero.", nameof(denominator));
}
this.num = numerator;
this.den = denominator;
}
// operator overload
public static Fraction operator +(Fraction a) => a;
public static Fraction operator -(Fraction a) => new Fraction(-a.num, a.den);
public static Fraction operator +(Fraction a, Fraction b) => new Fraction(a.den * b.num + a.num * b.den, a.den * b.den);
public static Fraction operator -(Fraction a, Fraction b) => a + (-b);
public static Fraction operator *(Fraction a, Fraction b) => new Fraction(a.num * b.num, a.den * b.den);
public override string ToString()
{
return $"{this.num}/{this.den}";
}
}
class Program
{
static void Main(string[] args)
{
Fraction fraction1 = new Fraction(1, 2);
Fraction fraction2 = new Fraction(3, 2);
Console.WriteLine($"{fraction1.ToString()} + {fraction2.ToString()} = {(fraction1+fraction2).ToString()}");
Console.WriteLine($"-{fraction1.ToString()} = {(-fraction1).ToString()}");
Console.WriteLine($"{fraction1.ToString()} - {fraction2.ToString()} = {(fraction1-fraction2).ToString()}");
Console.WriteLine($"{fraction1.ToString()} * {fraction2.ToString()} = {(fraction1*fraction2).ToString()}");
Console.ReadKey();
}
}
}
7.修改一个字符串
字符串在.Net中是不可修改的,对字符串进行的增删的结果都是新生成一个字符串再返回的，下面以实例说明。
using System;
namespace StringModifier
{
class Program
{
var source="The mountains are behind the clouds today.";
static void Main(string[] args)
{
var replaced=source.Replace("behind","front");
Console.WriteLine($"source:{source}");
Console.WriteLine($"replaced:{replaced}");
Console.ReadKey();
}
}
}
8.判断一个字符串是不是数值类型的
可以用tryparse方法来进行判断，下面是实例说明：
using System;
namespace ConsoleApp1
{
class Program
{
static void Main(string[] args)
{
int i = 0;
bool res = int.TryParse("2", out i);
if(res)
{
Console.WriteLine($"{i+1}");
}
i = 0;
bool res1 = int.TryParse("we2", out i);
if (res)
{
Console.WriteLine($"{i}");
}
Console.ReadKey();
}
}
}
9.用LINQ查询ArrayList
using System;
using System.Collections;
using System.Linq;
namespace ConsoleApp1
{
class Student
{
public string FirstName { get; set; }
public string LastName { get; set; }
public int[] Scores { get; set; }
public override string ToString()
{
string res = string.Empty;
res += "FirstName：" + this.FirstName+"\t";
res += "LastName：" + this.LastName+"\t";
for(int i=0;i<this.Scores.Length;i++)
{
res += $"第{i+1}个科目成绩为:{this.Scores[i]}"+"\t";
}
return res;
}
}
class Program
{
static void Main(string[] args)
{
ArrayList list = new ArrayList();
list.Add(new Student { FirstName = "张", LastName = "三", Scores = new int[] { 100, 90 } });
list.Add(new Student { FirstName = "李", LastName = "四", Scores = new int[] { 98, 90 } });
list.Add(new Student { FirstName = "张", LastName = "六", Scores = new int[] { 96, 90 } });
list.Add(new Student { FirstName = "张", LastName = "八", Scores = new int[] { 90, 80 } });
var query = from Student stu in list
where stu.Scores[0] > 95 && stu.FirstName == "张"
select stu;
foreach(var item in query)
{
Console.WriteLine(item);
}
Console.ReadKey();
}
}
}
10.LINQ查询中使用lambda表达式
using System;
using System.Collections;
using System.Linq;
namespace ConsoleApp1
{
class Program
{
static void Main(string[] args)
{
// Data source
int[] scores = new int[] { 100, 50, 60, 70, 40, 98, 78, 69 };
// The call to count forces iteration of the source
int highScoreCount = scores.Where(x => x > 90).Count();
Console.WriteLine(highScoreCount);
Console.ReadKey();
}
}
}
11.LINQ中的运算符All,Any,Contains的用法
All和Any运算符都返回一个布尔类型的结果，All是当所有的数值都满足条件时才会返回True,Any是只要存在满足条件的数值就返回True。Contains是模糊匹配
using System;
using System.Collections.Generic;
using System.Linq;
namespace ConsoleApp1
{
class Market
{
public string Name { get; set; }
public string[] Items { get; set; }
}
class Program
{
static void Main(string[] args)
{
List<Market> markets = new List<Market>
{
new Market { Name = "Emily's", Items = new string[] { "kiwi", "cheery", "banana" } },
new Market { Name = "Kim's", Items = new string[] { "melon", "mango", "olive" } },
new Market { Name = "Adam's", Items = new string[] { "kiwi", "apple", "orange" } },
new Market { Name = "Adam1's", Items = new string[] { "kiwi","yakiwi","apple", "orange" } },
};
// Determine which market have all fruit names length equal to 5
IEnumerable<string> names = from market in markets
where market.Items.All(item => item.Length == 5)
select market.Name;
// Determine which market have all fruit names length equal to 5
IEnumerable<string> names2 = from market in markets
where market.Items.Any(item => item.Length == 4)
select market.Name;
IEnumerable<string> containsNames = from market in markets
where market.Items.Contains("kiwi")
select market.Name;
Console.WriteLine("All");
foreach (string name in names)
{
Console.WriteLine($"{name} market");
}
Console.WriteLine("Any");
foreach (string name in names2)
{
Console.WriteLine($"{name} market");
}
Console.WriteLine("Contains");
foreach(var item in containsNames)
{
Console.WriteLine(item);
}
}
}
}
12.LINQ中使用排序
- 按照一个值来排序
using System;
using System.Collections.Generic;
using System.Linq;
namespace ConsoleApp1
{
class Student
{
public string Name { get; set; }
public int Score { get; set; }
}
class Program
{
static void Main(string[] args)
{
List<Student> students = new List<Student>();
for(int i=0;i<30;i++)
{
Student stu = new Student
{
Name = "Name" + i.ToString(),
Score = new Random().Next(100)
};
students.Add(stu);
}
var query = from Student stu in students
where stu.Score > 60//过滤成绩几个的同学
orderby stu.Score//按成绩排序
select stu;
foreach (var item in query)
{
Console.WriteLine("Name:"+item.Name+"\t"+"Score:"+item.Score);
}
Console.ReadKey();
}
}
}
// 运行结果
Name:Name1 Score:74
Name:Name14 Score:76
Name:Name16 Score:76
Name:Name23 Score:76
Name:Name2 Score:77
Name:Name13 Score:86
Name:Name21 Score:88
Name:Name22 Score:91
Name:Name3 Score:92
Name:Name20 Score:93
- 按照里两个值来排序,如果数学成绩相等，再比较文化课成绩
using System;
using System.Collections.Generic;
using System.Linq;
namespace ConsoleApp1
{
class Student
{
public string Name { get; set; }
public int MathScore { get; set; }
public int CultureScore { get; set; }
}
class Program
{
static void Main(string[] args)
{
List<Student> students = new List<Student>();
for(int i=0;i<30;i++)
{
Student stu = new Student
{
Name = "Name" + i.ToString(),
MathScore = new Random().Next(90,100),
CultureScore = new Random().Next(100),
};
students.Add(stu);
}
var query = from Student stu in students
where stu.MathScore > 60 && stu.CultureScore>60
orderby stu.MathScore,stu.CultureScore
select stu;
foreach (var item in query)
{
Console.WriteLine("Name:"+item.Name+"\t"+"MathScore:"+item.MathScore+"\t"+"CultureScore:"+item.CultureScore);
}
Console.ReadKey();
}
}
}
转载：https://blog.csdn.net/yasenRK/article/details/105691001
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