C# Console 學習筆記


  1. 綜合
    1. 存取 App.config Key
    2. 資料庫存取
    3. IO 資料讀入
    4. Struct
    5. 存取 Local JSON File
    6. 大數運算
  2. 物件導向
    1. 物件的建構
    2. 建構子的繼承 / 呼叫父類別的建構子 Constructor Inheritance
    3. is / as Operator
    4. Virtual / Override / Sealed
    5. Out 參數修飾
    6. Readonly 修飾詞
    7. Null 條件運算子 (C#6)
    8. 封裝 Field 與讀取 Property 的範例
    9. 取得執行中物件的型別 (typeof / GetType)
  3. 字串處理
  4. 集合類型
    1. 集合類型的初始建構 Collection initializers
    2. 匿名類型建構 Anonymous Types
    3. 匿名類型的集合建構 List of Anonymous Types
    4. 索引子範例 Examples of Indexer
    5. 字典示範 (Examples of Dictionary)

C# is good to use and good to learn.

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綜合

存取 App.config Key

步驟1:加入參考:System.Configuration

步驟2:設定 App.config

<configuration>
    <appSettings>
      <add key="configKey" value="configValue"/>
    </appSettings>
</configuration>

步驟3:程式引用 config 值

using System.Configuration;

static void Main(string[] args)
{
    Console.WriteLine(ConfigurationManager.AppSettings["configKey"]);
}

資料庫存取

⚡如果要 Insert String 包含中文等文字,必須要在 quote mark 之前加入N。

Insert Into tbName Values(N'櫻花', N'さくら');

🦄 否則必須使用 SqlCommand.Parameters

SqlCommand cmd = new SqlCommand();
cmd.CommandText = "insert into tbName (item) values (@flower)";
cmd.Parameters.Add("@flower", SqlDbType.NVarChar).Value = "さくら";

資料庫存取的範例

using System.Data.SqlClient;

static void Main(string[] args)
{
    string Constr = "Persist Security Info=False; Integrated Security=true; \
        Initial Catalog=...;Server=...;";

    SqlConnection dataConnection = new SqlConnection { ConnectionString = Constr };
    dataConnection.Open();
    SqlCommand mySqlCmd = new SqlCommand("Insert into ...", dataConnection);
    mySqlCmd.ExecuteNonQuery();
    dataConnection.Close();
}

IO 資料讀入

string text = System.IO.File.ReadAllText(@"C:\filePath\file.txt", 
    System.Text.Encoding.Default);

Struct

struct屬於value type,因此在複製時是直接複製一份而非複製參考。而value type不可以被指為null,反之,reference type則可以。除非是nullable value type


public struct Point { public int X, Y; }

static void Main()
{
	Point p1 = new Point();
	p1.X = 7;
	
	Point p2 = p1;             // Assignment causes copy
	
	Console.WriteLine (p1.X);  // 7
	Console.WriteLine (p2.X);  // 7
	
	p1.X = 9;                  // Change p1.X
	
	Console.WriteLine (p1.X);  // 9
	Console.WriteLine (p2.X);  // 7
}

存取 Local JSON File

using System.IO;
using Newtonsoft.Json;

public static List<AuthMember> readJson()
{
  var r = new List<AuthMember>{};
  using (var sr = new StreamReader(
      System.Web.HttpContext.Current.Server.MapPath("~/App_Data/member.json")))
  {
      r = JsonConvert.DeserializeObject<List<AuthMember>>(sr.ReadToEnd());
  }
  return r;
}

大數運算

using System.Numerics;
BigInteger bigIntFromInt64 = new BigInteger(12345678901234567890);
Console.WriteLine(bigIntFromInt64);

string positiveString = "123456789012345678901234567890";
BigInteger posBigInt = BigInteger.Parse(positiveString);
Console.WriteLine(posBigInt);

😋

物件導向

物件的建構

避免濫用 Constructor Overloadding ,如果只是不同 Fileds 的建構情境用 Object Initializer 替代,Object Initializer 是使用不含引數格式的建構子來進行,如果當此建構子不能被存取,使用 Object Initializer 就會發生錯誤。

public class Point{
    public int X {get; set;}
    public int Y {get; set;}
}

new Point{ X = 5, Y = 15};

MSDN - How to initialize objects by using an object initializer

建構子的繼承 / 呼叫父類別的建構子 Constructor Inheritance

public class Subclass : Baseclass
{
	public Subclass (int x) : base (x) { }
}

is / as Operator

  • is : 判斷變數是否指向特定型別(明確指定)
  • as : 將型別轉型,若轉型失敗會指向null而非拋出錯誤

Virtual / Override / Sealed

class 方法有被 virtual 修飾的可以被繼承的 sub class override,如果沒有特別指定 virtual 與 override 則 sub class 會隱藏 pareant method。若方法被 sealed override,則不能再被繼承者 override。

Out 參數修飾

讓引數變成 Reference Value,可以讓函數外的變數接收函數內的值;在使用 TryParse 時會用到。

int initializeInMethod;
OutArgExample(out initializeInMethod);
Console.WriteLine(initializeInMethod);     // value is now 44

void OutArgExample(out int number)
{
    number = 44;
}

string numberAsString = "1640";

int number;
if (Int32.TryParse(numberAsString, out number))
    Console.WriteLine($"Converted '{numberAsString}' to {number}");
else
    Console.WriteLine($"Unable to convert '{numberAsString}'");
// The example displays the following output:
//       Converted '1640' to 1640

MDSN - Out

Readonly 修飾詞

可以保證 Field 只被初始化一次,並且不會重複初始化以免讓資料流失。

public class Customer
{
    public readonly List<Order> Orders = new List<Order>(); //物件建構時,自動初始化
}

Null 條件運算子 (C#6)

C# Null Conditional Operator, Null 條件運算子

封裝 Field 與讀取 Property 的範例

public class Person
{
    public DateTime BirthDate {get; set;}
    public int Age {
        get {
            var timespan = DateTime.Now - BirthDate;
            return timespan.Days / 365;
        }
    }

}

取得執行中物件的型別 (typeof / GetType)

p.GetType().Name             
typeof (Point).Name          

字串處理

C# String 字串處理

集合類型

集合類型的初始建構 Collection initializers

List<int> digits = new List<int> { 0, 6, 1, 9 };
List<string> fruits = new List<string> { "Mango", "Lichee", "Lemon" };
List<Point> points = new List<Point> { new Point{X = 3, Y = 5}, new Point{X = 2, Y = 7} };

var dict = new Dictionary<int, StudentName>()
{
    { 017, new StudentName { Name = "sdwh", ID = 5017 } },
    { 028, new StudentName { Name = "phym", ID = 5028 } },
    { 099, new StudentName { Name = "mike", ID = 5099 } }
};

MSDN - Object and Collection Initializers (C# Programming Guide)

匿名類型建構 Anonymous Types

var pet = new { Age = 10, Name = "Fluffy" };

MSDN - Anonymous Types

匿名類型的集合建構 List of Anonymous Types

var anonArray = new[] {
    new { name = "apple", number = 4 },
    new { name = "grape", number = 1 },
};

foreach (var fruit in anonArray)
{
    Console.WriteLine($"{fruit.name} {fruit.number}");
}

索引子範例 Examples of Indexer

範例 1

public class HttpCookie
{
    private readonly Dictionary<string, string> _dictionary;
    public DateTime Expire {get; set;}

    public HttpCookie()
    {
        _dictionary = new Dictionary<string, string>();
    }
    
    public string this[string key]
    {
        get { return _dictionary[key];}
        set { _dictionary[key] = value;}
    }
}

範例 2


class Sentence
{
    string[] words = "The quick brown fox".Split();

    public string this [int wordNum]      // indexer
    { 
        get { return words [wordNum];  }
        set { words [wordNum] = value; }
    }
}

static void Main()
{		
    Sentence s = new Sentence();
    Console.WriteLine (s[3]);       // fox
    s[3] = "kangaroo";
    Console.WriteLine (s[3]);       // kangaroo
}

字典示範 (Examples of Dictionary)

var d = new Dictionary<string, int>();

d.Add("One", 1);
d["Two"] = 2;     // adds to dictionary because "two" not already present
d["Two"] = 22;    // updates dictionary because "two" is now present
d["Three"] = 3;

Console.WriteLine (d["Two"]);                // Prints "22"
Console.WriteLine (d.ContainsKey ("One"));   // true (fast operation)
Console.WriteLine (d.ContainsValue (3));     // true (slow operation)
int val = 0;

if (!d.TryGetValue ("onE", out val))
	Console.WriteLine ("No val");            // "No val" (case sensitive)

// Three different ways to enumerate the dictionary:

foreach (KeyValuePair<string, int> kv in d)          //  One ; 1
	Console.WriteLine (kv.Key + "; " + kv.Value);    //  Two ; 22
                                                     //  Three ; 3


foreach (string s in d.Keys) Console.Write (s);      // OneTwoThree
Console.WriteLine();
foreach (int i in d.Values) Console.Write (i);       // 1223
Console.WriteLine();