Basic
Glossary
Private fields:
Can only be accessed by methods in the class (via getter and setter) and
they are not accessible by subclasses or instantiation.
Protected fields:
Can only be accessed by methods in the class and by subclasses.
Read-only fields:
Set at runtime at constructors and can't be changed.
Method overloading:
When you have different versions of method
Method override:
when you replace a method
Generic can only store one type
Non generic can store many typesTryGetValue
if (!xlRow.Cell(SchemesExcelColumn.Version).TryGetValue(out int version))
{
version = 1;
}
// If successfull, you get version. If not, you get version = 1 as default
if (results.TryGetValue(conditionBankId, out var conditionTemplateDtos))
{
conditionTemplateDtos.Add(conditionTemplateDto);
}
else
{
results.Add(conditionBankId,
new List<ConditionTemplateDto> {conditionTemplateDto});
}
// If successful of retrieving the conditionBankId (key) in RESULTS,
// you out the list of conditionTemplateDtos and add the conditionTemplateDto
// If fail, you add the RESULTS with conditionBankId as key
// and initiliaze the new list as valueVerbatim String
// verbatim ignore \n
Console.WriteLine(@"you \n have no power here");
// good example is
// Console.WriteLine(@"C:\User\Admin\Doc\Super Cool.png");
// without verbatim, it will escape due to \ and give error
Console.WriteLine("you \n have power here");Null
Data types by default cannot have a value of null.
When null is needed, add question mark:
int? randNum = null;Casting
// If you want to cast from one type to another - conversion
long num1 = 1234;
int num2 = (int)num1;
Console.WriteLine("Orig : {0} Cast : {1}", num1.GetType(), num2.GetType());
//Int64 and Int32Pass by Value vs Pass by Reference
// By default values are passed into a method
// and not a reference to the variable passed
// Changes made to those values do not effect the variables outside of the method
// To pass by reference:
int num1 = 10;
int num2 = 20;
Console.WriteLine("Before Swap num1 : {0} num2 : {1}", num1, num2); // 10 and 20
Swap(ref num1, ref num2);
Console.WriteLine("After Swap num1 : {0} num2 : {1}", num1, num2); // 20 and 10
public static void Swap(ref int num1, ref int num2)
{
int temp = num1;
num1 = num2;
num2 = temp;
}
static void Main(string[] args)
{
int a = 1;
int b = a;
Console.WriteLine(a); // 1
Console.WriteLine(b); // 1
a = 5;
Console.WriteLine(a); // 5
Console.WriteLine(b); // 1, not affected by the change
Test(a);
Console.WriteLine(a); // 5, not affected by the method
Console.WriteLine(b); // 1
int[] c = { 10 };
int[] d = c;
Console.WriteLine(c[0]); // 10
Console.WriteLine(d[0]); // 10
d[0] = 20;
Console.WriteLine(c[0]); // 20 // affected by the change
Console.WriteLine(d[0]); // 20
}
static void Test(int a)
{
a = 100;
}Params Modifier
static double GetSumMore(int num1, int num2, params double[] nums)
GetSumMore( 1, 2, 3, 4) // num1 is 1, num2 is 2 and the rest is params (3,4)Array
int[] luckyNumbers = { 4, 7, 10 }
var employees = new[] { "Mike", "Paul", "Rick" };
// Create array with values
string[] friends = new string[5];
// Create array with empty values with length of 5
//Multi-Dimensional Array
int[ , ] numberGrid = {
{1, 2 },
{3, 4 },
{5, 6 }
};
int [ , ] = new int [2, 3]
// Create 2D array - 2 row and 3 columns (elements)Exception Handler - Prevent program from exiting and handle the error
try {
// Your code block
}
catch (Exception e) {
Console.WriteLine (e.Message)
}
// OR
catch (FormatException e) {
// Your code block to handle FormatException
}
catch (DivideByZeroException) {
// Your code block to handle DivideByZeroException
}
finally {
// Always get executed no matter what
}Constructor
class Book
{
public string title;
public string author;
public int pages;
// You can have many constructor inside a class, including empty constructor
public Book (string aTitle, string aAuthor, int aPages )
{
title = aTitle;
author = aAuthor;
pages = aPages;
}
}
// constructor overloading - Use with caution as it clutter the code
class Customer
{
public int Id;
public string Name;
public readonly List<Order> Orders = new List<Order>();
// initilize customer with order list and readonly prevent re-initilization
public Customer (int id)
{
this.Id = id;
}
public Customer(int id, string name) : this(id) // called constructor with id
{
this.Name = name
}
}Getter and Setter
// Using getter as read-only property
class Player
{
private int _heatlh = 100
public int health
{
get
{
return _health
}
}
public void Damage (int _dmg)
{
_health -= _dmg
}
}
Player tom = new Player();
tom.Damage(10) // OK
tom.health = 80 // Not OK as it is Read Only
Console.Writeline(tom.health)// Print 90
// Using setter to prevent invalid value in object creation
class Movie
{
public string title;
public string director;
private string rating;
public Movie (string aTitle, string aDirector, string aRating ) {
title = aTitle;
director = aDirector;
Rating = aRating;
}
public string Rating {
get { return rating; }
set {
if (value == "G" || value == "R" || value == "NR") {
rating = value
} else {
rating = "NR"
}
}
}
// You can have the getters and setters likt this and also set the default value
public string Owner { get; set; } = "No Owner"; Static - Class Static Attribute and Static Method and Static Class
// Class static attribute is about the class and not the object.
// So, static attribute is shared in all instances.
class Song
{
public string title;
public string artist;
public static int songCount = 0;
public Song (string aTitle, string aArtist ) {
title = aTitle;
artist = aArtist;
songCount++
}
public int getSongCount( ) {
return songCount;
}
}
Song holiday = new Song ("Holiday", "Green Day", 200);
// Another way to create object
Song holiday = new Song () { title= "Holiday", artist = "Green Day" }
Console.WriteLine(Song.songCount) // 1
Console.WriteLine(holiday.songCount ) // Not accessible
Console.WriteLine(holiday.getSongCount()) // Onlt accesible through object method
// Static Methods & Class
static class usefulTools // Static Class means you cannot create an instance
{
public static void SayHi( string name )
// without the word static, you need to create an object to access the method
{
ConsoleWriteLine("hi" + name)
}
}
UsefulTools.SayHi("Ben")
// So you can just call it from the class without creating an objectInner Class
// You can create inner classes that are normally helper classes for the outer
// class because it can access private members of the outer class
class Animal {
public class AnimalHealth {
public bool HealthyWeight(double height, double weight) {
double calc = height / weight;
if ((calc >= .18) && (calc <= .27)) {
return true;
}
else return false;
}
}
}
Animal.AnimalHealth getHealth = new Animal.AnimalHealth();
Console.WriteLine("Is my animal healthy : {0}", getHealth.HealthyWeight(11, 46));Inheritance - Is-A relationship (Dog Class is Animal Class)
// Italian chef override method of normal chef
public override void MakeSpecialDish() {
Console.WriteLine("Cook Spagethi");
}
// Normal chef method that can be overriden by sub-class
public virtual void MakeSpecialDish () {
Console.WriteLine("Cook BBQ Ribs");
}Aggregation or Delegate - Has-A relationship (Animal Class has a Animal Id Info Class)
class Animal {
protected AnimalIDInfo animalIDInfo = new AnimalIDInfo();
public void SetAnimalIDInfo(int idNum, string owner) {
animalIDInfo.IDNum = idNum;
animalIDInfo.Owner = owner;
}
}
class AnimalIDInfo {
public int IDNum { get; set; } = 0;
public string Owner { get; set; } = "No Owner";
}Polymorphism
class Animal {
public void MakeSound() {
Console.WriteLine($"{Name} says {Sound}");
}
// You can define 2 Animal objects but have one actually be a Dog type.
Animal monkey = new Animal() { Name = "Happy", Sound = "Eeeeee" };
Animal spot = new Dog() { Name = "Spot", Sound = "Wooooff", Sound2 = "Geerrrr" };
spot.makeSound() // spot says Wooooff (without the sound2)
// With polymorphism with virtual and override
// This is an example of how Polymorphism allows a subclass to override a method
// in the super class and even if the subclass is defined as the super class
// type the correct method will be called
class Animal {
public virtual void MakeSound() {
Console.WriteLine($"{Name} says {Sound}");
}
class Dog : Animal {
public override void MakeSound() {
Console.WriteLine($"{Name} says {Sound} and {Sound2}");
}
}
spot.makeSound() // spot says Wooooff and Geerrrr
// Another example of polymorphism
abstract class Shape {} // abstract is a clss that you don't want to instantiate
class Circle : Shape {}
class Rectangle : Shape {}
Shape[] shapes = {new Circle(5), new Rectangle(4,5)};
foreach(Shape s in shapes) {
Circle testCirc = s as Circle; // Use "as" to check if an object is of a specific type
if(testCirc == null) {
Console.WriteLine("This isn't a Circle");
}
if(s is Circle) { // Use "is" to check the data type
Console.WriteLine("This isn't a Rectangle");
}
}
List, Dictionary, Tuple
// Array with dynamic size use List and it can only consist of one data type
List <int> numbers = new List<int> ();
number.Add(1); // OK
number.Add("Hello"); // Not OK
// Dictionary<TKey, TValue>
Dictionary<string, int> myDictionary = new Dictionary<string, int>();
myDictionary.Add("a", 100);
myDictionary.Add("b", 200);
Console.WriteLine(myDictionary["a"]); // 100
// Tuple, carry different type of data
public Tuple<string, int> Math(int a, int b)
{
string c = "Hello World";
int d = a * b;
return Tuple.Create(c, d);
}
static void Main(string[] args)
{
Program p = new Program();
var obj = p.Math(10, 20);
Console.WriteLine(obj.Item1); // Hello World
Console.WriteLine(obj.Item2); // 200
}
// New way to create tuple
public (string Hello, int Multiply) Math(int a, int b)
{
string c = "Hello World";
int d = a * b;
return (c, d);
}
static void Main(string[] args)
{
Program p = new Program();
var obj = p.Math(10, 5);
Console.WriteLine(obj.Hello);
Console.WriteLine(obj.Multiply);
} Enum
enum Breed { Bulldog, Boxer, Chihuahua };
class Dog
{
public Breed breed;
public Dog(Breed _breed)
{
breed = _breed
}
}
Dog spotty = new Dog(Breed.Bulldog / Breed.Boxer/ Breed.Chihuahua)
Console.WriteLine(spotty.breed);
enum CarColor : byte // initialize to byte, the default is integer
{
Orange = 1, // initialize to 1, the default is 0
Blue,
Green,
Red,
Yellow
}
static void Main(string[] args)
{
CarColor car1 = CarColor.Yellow;
PaintCar(car1);
}
static void PaintCar(CarColor cc)
{
Console.WriteLine("The car was painted {0} with the code {1}",
cc, (byte)cc);
}Interface
Interface is like a contract... Why not use base class? Because you can derive from multiple interfaces
Generics
Handle unknown data types
// Generic method inside non-generic class
class Utility
{
public static bool CompareValues<T01, T02> (T01 value1, T02 value2)
{
return value1.Equals(value2);
}
public static bool CompareTypes<T01, T02> (T01 type1, T02 type2)
{
return typeof(T01).Equals(typeof(T02));
}
}
Console.WriteLine(Utility.CompareValues(10, "Hello")); // FALSE
Console.WriteLine(Utility.CompareTypes("World", "Hello")); // TRUEDependency Injection - Add Singleton, Add Scoped and Add Transient
Service Type | In the scope of a given HTTP request | Across different HTTP request |
Scoped Service | Same Instance | New Instance |
Singleton Service | Same Instance | Same Instance |
Transient Service | New Instance | New Instance |
Defensive Programming - Mosh
//Preventing the count greater than no of elements in the list or count is 0 of less than 0
if (count > list.Count || count <= 0)
{
//first arguement is the parameter
//second arguement is the message we want to show
throw new ArgumentOutOfRangeException("count", "Count should be between 1 and the number of elements in the list");
}
//Preventing a null being thrown as the list
if (list == null)
{
throw new ArgumentNullException("list");
}Different type of access modifier: private, public, protected and internal. Link
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