csharp cheatsheet
1.0.0
综合C＃备忘单旨在帮助开发人员掌握与C＃编程相关的密钥语法和概念。
基本结构
数据类型
变量
常数
有条件的语句
循环
数组
列表
字典
方法
类和对象
例外处理
代表，活动和Lambdas
LINQ（语言集成查询）
属性
异步/等待
各种各样的
字符串操纵
文件I/O。
日期和时间
仿制药
无效
属性和反思
扩展方法
依赖注入
部分类
互操作性
匿名类型
元组
模式匹配
本地功能
记录
带有表达
索引和范围
使用声明
无效的参考类型（NRTS）
基于模式的使用
属性模式
默认接口实现
动态结合
所有C＃程序都遵循以下概述的基本结构：
using System;
public class HelloWorld
{
public static void Main(string[] args)
{
Console.WriteLine("Hello, World!");
}
}
从.NET 5开始，顶级语句简化了程序。CS内容：
Console.WriteLine("Hello, World");
C＃支持各种数据类型，例如：
价值类型：int，char，float
参考类型：字符串，类，数组
变量是值的符号名称：
int age = 30; // integer variable
string name = "John"; // string variable
double PI = 3.14159; // double for floating-point numbers
bool isLoggedIn = true; // boolean variable
使用“ var”进行类型推广：
var number = 5; // compiler infers type as int
var message = "This is a message"; // compiler infers type as string
常数具有不变的价值：
const double GRAVITY = 9.81; // constant for gravitational acceleration
const string COMPANY_NAME = "MyCompany"; // constant company name
基于条件的控制程序流量：
int age = 20;
if (age >= 18)
{
Console.WriteLine("You are eligible to vote.");
}
else
{
Console.WriteLine("You are not eligible to vote.");
}
switch (variable) { /*...*/ } // Switch statement
重复执行代码：
for (int i = 1; i <= 5; i++)
{
Console.WriteLine(i);
}
foreach (var item in collection) { /*...*/ } // Foreach loop
while (condition) { /*...*/ } // While loop
do { /*...*/ } while (condition); // Do-while loop
固定大小的要素集合：
string[] names = new string[3] { "Alice", "Bob", "Charlie" };
Console.WriteLine(names[1]); // Output: Bob (accessing element at index 1)
动态集合类似于数组：
List<int> numbers = new List<int>();
numbers.Add(1);
numbers.Add(2);
numbers.Add(3);
foreach (var number in numbers)
{
Console.WriteLine(number);
}
数据关联的键值对：
Dictionary<string, string> phonebook = new Dictionary<string, string>();
phonebook.Add("John Doe", "123-456-7890");
phonebook.Add("Jane Doe", "987-654-3210");
Console.WriteLine(phonebook["John Doe"]); // Output: 123-456-7890
封装可重复使用的逻辑：
public class Rectangle
{
public double Width { get; set; }
public double Height { get; set; }
public double GetArea()
{
return Width * Height;
}
}
public class Program
{
public static void Main(string[] args)
{
Rectangle rect = new Rectangle();
rect.Width = 5;
rect.Height = 10;
double area = rect.GetArea();
Console.WriteLine($"Area of rectangle: {area}");
}
}
类定义对象的蓝图：
public class MyClass // Class definition
{
public string PropertyName { get; set; } // Properties store data
public void MethodName() { /*...*/ } // Methods define actions
}
MyClass obj = new MyClass(); // Object creation
优雅地管理运行时错误：
public static int GetNumberInput()
{
while (true)
{
try
{
Console.WriteLine("Enter a number: ");
string input = Console.ReadLine();
return int.Parse(input);
}
catch (FormatException)
{
Console.WriteLine("Invalid input. Please enter a number.");
}
}
}
public static void Main(string[] args)
{
int number = GetNumberInput();
Console.WriteLine($"You entered: {number}");
}
用于事件驱动的编程和方法处理：
public delegate void MyDelegate(); // Delegate declaration
event MyDelegate MyEvent; // Event declaration
public class Person
{
public string Name { get; set; }
public int Age { get; set; }
}
public static void Main(string[] args)
{
List<Person> people = new List<Person>()
{
new Person { Name = "Alice", Age = 30 },
new Person { Name = "Bob", Age = 25 },
new Person { Name = "Charlie", Age = 40 },
};
people.Sort((p1, p2) => p1.Name.CompareTo(p2.Name));
foreach (var person in people)
{
Console.WriteLine(person.Name); // Output: Alice, Bob, Charlie (sorted by name)
}
}
数据操作的查询功能：
using System.Linq;
public static void Main(string[] args)
{
List<int> numbers = new List<int>() { 1, 2, 3, 4, 5, 6 };
var evenNumbers = numbers.Where(x => x % 2 == 0);
foreach (var number in evenNumbers)
{
Console.WriteLine(number); // Output: 2, 4, 6
}
}
将元数据添加到代码元素：
[Obsolete("Use the new DoSomethingV2 method instead.")]
public void DoSomething()
{
// Implementation here
}
public void DoSomethingV2()
{
// New and improved implementation
}
对于非阻滞代码执行：
using System.Threading.Tasks;
public static async Task DownloadFileAsync(string url, string filePath)
{
// Simulate downloading data asynchronously
await Task.Delay(2000); // Simulate a 2-second download
// Write downloaded data to the file
File.WriteAllText(filePath, "Downloaded content");
Console.WriteLine($"File downloaded to: {filePath}");
}
public static void Main(string[] args)
{
string url = "https://example.com/data.txt";
string filePath = "downloaded_data.txt";
DownloadFileAsync(url, filePath);
// Continue program execution while download happens in the background
Console.WriteLine("Downloading file...");
Console.WriteLine("Meanwhile, you can do other things...");
}
其他语言功能：
枚举，界面，类，记录，结构
动态，as，as var namef
强大的字符串处理方法：
string.Concat(); // Combine strings
string.Join(); // Join elements
str.Split(); // Split string
str.ToUpper(); // Convert to uppercase
str.ToLower(); // Convert to lowercase
带有文件的操作：
using System.IO; // Required for File I/O
File.ReadAllText(path); // Read file content
File.WriteAllText(path, content); // Write to file
File.Exists(path); // Check file existence
日期和时间操纵：
using System;
public static void Main(string[] args)
{
DateTime startDate = DateTime.Parse("2024-03-10");
DateTime endDate = DateTime.Now;
TimeSpan difference = endDate - startDate;
Console.WriteLine($"Time difference: {difference.Days} days, {difference.Hours} hours");
}
类型安全数据结构：
public class Stack<T>
{
private List<T> items = new List<T>();
public void Push(T item)
{
items.Add(item);
}
public T Pop()
{
T item = items[items.Count - 1];
items.RemoveAt(items.Count - 1);
return item;
}
}
public static void Main(string[] args)
{
Stack<string> messages = new Stack<string>();
messages.Push("Hello");
messages.Push("World");
string message = messages.Pop();
Console.WriteLine(message); // Output: World
}
允许价值类型为null：
int? nullableInt = null; // Nullable integer
元数据和类型内省：
public class Person
{
public string Name { get; set; }
public int Age { get; set; }
}
public static void Main(string[] args)
{
Type personType = typeof(Person);
PropertyInfo[] properties = personType.GetProperties();
foreach (PropertyInfo property in properties)
{
Console.WriteLine(property.Name); // Output: Name, Age
}
}
将方法添加到现有类型：
public static class StringExtensions
{
public static string ToUppercase(this string str)
{
return str.ToUpper();
}
}
public static void Main(string[] args)
{
string message = "Hello, world!";
string uppercased = message.ToUppercase(); // Using the extension method
Console.WriteLine(uppercased); // Output: HELLO, WORLD!
}
松散耦合代码设计：
public interface ILogger
{
void LogMessage(string message);
}
public class MyService
{
private readonly ILogger _logger;
public MyService(ILogger logger)
{
_logger = logger;
}
public void DoSomething()
{
_logger.LogMessage("Doing something...");
}
}
// Implementing the ILogger interface (example)
public class ConsoleLogger : ILogger
{
public void LogMessage(string message)
{
Console.WriteLine(message);
}
}
public static void Main(string[] args)
{
ILogger logger = new ConsoleLogger();
MyService service = new MyService(logger);
service.DoSomething();
}
拆分单个类的定义：
public partial class MyClass { /*...*/ } // Partial class definition
与其他语言互动：
using System;
using System.Runtime.InteropServices;
[DllImport("user32.dll")]
public static extern int MessageBox(IntPtr hWnd, string lpText, string lpCaption, uint uType);
public static void Main(string[] args)
{
MessageBox(IntPtr.Zero, "Hello from C#!", "Interop Example", 0);
}
创建未命名类型：CSHARPCOPY代码
var person = new { Name = "John", Age = 30 };
Console.WriteLine($"Name: {person.Name}, Age: {person.Age}");
具有特定数量元素的数据结构：
(string Name, int Age) person = ("Alice", 30);
Console.WriteLine($"Name: {person.Name}, Age: {person.Age}"); // Accessing elements using Item1 and Item2
简化了某些编程任务：
object obj = new Person { Name = "Bob", Age = 25 };
if (obj is Person { Name: "Bob", Age >= 18 })
{
Console.WriteLine("Bob is an adult.");
}
将逻辑封装在方法中：
public static int Calculate(int number)
{
int Factorial(int n)
{
if (n == 0) return 1;
return n * Factorial(n - 1);
}
return Factorial(number);
}
public static void Main(string[] args)
{
int result = Calculate(5);
Console.WriteLine($"5! = {result}");
}
参考类型的简明语法：
public record Person(string Name, int Age);
public static void Main(string[] args)
{
Person person1 = new Person("Alice", 30);
Person person2 = new Person("Alice", 30);
// Records provide default equality comparison
if (person1 == person2)
{
Console.WriteLine("People are equal");
}
}
记录的无损突变：
var john = new Person("John", 30);
var jane = john with { Name = "Jane" }; // Non-destructive mutation
灵活的数据访问：
int[] arr = {0, 1, 2, 3, 4, 5};
var subset = arr[1..^1]; // Indexer and range usage
处理IDIsposable对象：
using var reader = new StreamReader("file.txt"); // using declaration
避免null参考例外：
public class Person
{
public string Name { get; set; }
public int Age { get; set; }
}
public static void Main(string[] args)
{
Person person = new Person() { Age = 30 };
// NRTs require null checks before accessing properties
if (person?.Name != null)
{
Console.WriteLine(person.Name);
}
else
{
Console.WriteLine("Name is null");
}
}
使用语句中的更多模式：
public ref struct ResourceWrapper { /*...*/ } // Resource wrapper
using var resource = new ResourceWrapper(); // Pattern-based using
在模式匹配中解构对象：
if (obj is Person { Name: "John", Age: var age }) { /*...*/ } // Property pattern matching
与默认方法实现的接口：
public interface IPerson { /*...*/ } // Interface with default method
public class MyClass : IPerson { /*...*/ } // Class implementing interface
运行时类型分辨率：
dynamic d = 5; // Dynamic binding
d = "Hello"; // No compile-time type checking
该结构化的C＃备忘单以高级主题和技术结束，为旨在增强其C＃编程技能的开发人员提供了全面的参考。有关详细的示例和进一步的探索，请参阅本指南中概述的特定部分。愉快的编码！
启发：https： //zerotomastery.io/cheatsheets/csharp-cheat-sheet/#constants
