observer

DesignPatternGuru/DesignPatternGuru.sln

@@ -43,6 +43,8 @@ Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Mediator", "Mediator\Mediat
 EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Memonto", "Memonto\Memonto.csproj", "{A6E39678-6214-4BD2-B616-A3350340E5AB}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Observer", "Observer\Observer.csproj", "{EB189FAC-7C63-48BB-92D7-3C35A277EA1D}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -117,6 +119,10 @@ Global
 		{A6E39678-6214-4BD2-B616-A3350340E5AB}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{A6E39678-6214-4BD2-B616-A3350340E5AB}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{A6E39678-6214-4BD2-B616-A3350340E5AB}.Release|Any CPU.Build.0 = Release|Any CPU
+		{EB189FAC-7C63-48BB-92D7-3C35A277EA1D}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{EB189FAC-7C63-48BB-92D7-3C35A277EA1D}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{EB189FAC-7C63-48BB-92D7-3C35A277EA1D}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{EB189FAC-7C63-48BB-92D7-3C35A277EA1D}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
@@ -139,6 +145,7 @@ Global
 		{6619433E-476B-404C-94A0-D0C0FE52DE41} = {E3B8A482-1A9A-4B6E-8310-050A44C8E379}
 		{08D296F6-6698-4FCB-B605-318D9381F975} = {E3B8A482-1A9A-4B6E-8310-050A44C8E379}
 		{A6E39678-6214-4BD2-B616-A3350340E5AB} = {E3B8A482-1A9A-4B6E-8310-050A44C8E379}
+		{EB189FAC-7C63-48BB-92D7-3C35A277EA1D} = {E3B8A482-1A9A-4B6E-8310-050A44C8E379}
 	EndGlobalSection
 	GlobalSection(ExtensibilityGlobals) = postSolution
 		SolutionGuid = {3E5A9C6B-2E8A-466E-B5E0-4379902EFFAC}

DesignPatternGuru/Observer/Observer.csproj

@@ -0,0 +1,10 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net6.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>

DesignPatternGuru/Observer/Observers/ConcreteObserverA.cs

@@ -0,0 +1,17 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Observer.Observers
+{
+    internal class ConcreteObserverA : IObserver
+    {
+        public void Update(ISubject subject)
+        {
+            if ((subject as Subject).State < 3)
+                Console.WriteLine("ConcreteObserverA: Reacted to the event.");
+        }
+    }
+}

DesignPatternGuru/Observer/Observers/ConcreteObserverB.cs

@@ -0,0 +1,17 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Observer.Observers
+{
+    internal class ConcreteObserverB : IObserver
+    {
+        public void Update(ISubject subject)
+        {
+            if ((subject as Subject).State == 0 || (subject as Subject).State >= 2)
+                Console.WriteLine("ConcreteObserverB: Reacted to the event.");
+        }
+    }
+}

DesignPatternGuru/Observer/Observers/IObserver.cs

@@ -0,0 +1,13 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Observer.Observers
+{
+    internal interface IObserver
+    {
+        void Update(ISubject subject);
+    }
+}

DesignPatternGuru/Observer/Observers/ISubject.cs

@@ -0,0 +1,17 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Observer.Observers
+{
+    internal interface ISubject
+    {
+        void Attach(IObserver observer);
+
+        void Detach(IObserver observer);
+
+        void Notify();
+    }
+}

DesignPatternGuru/Observer/Observers/Subject.cs

@@ -0,0 +1,48 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Observer.Observers
+{
+    internal class Subject : ISubject
+    {
+        public int State { get; set; } = -0;
+
+        private List<IObserver> _observers = new List<IObserver>();
+
+        public void Attach(IObserver observer)
+        {
+            _observers.Add(observer);
+            Console.WriteLine("Subject: Attached an observers.");
+        }
+
+        public void Detach(IObserver observer)
+        {
+            _observers.Remove(observer);
+            Console.WriteLine("Subject: Detached an observers.");
+        }
+
+        public void Notify()
+        {
+            Console.WriteLine("Subject: Notifying observers...");
+            foreach (IObserver observer in _observers)
+            {
+                observer.Update(this);
+            }
+        }
+
+        public void SomeBusinessLogic()
+        {
+            Console.WriteLine();
+            Console.WriteLine("Subject: I'm doing something important.");
+            this.State = new Random().Next(0, 10);
+
+            Thread.Sleep(15);
+
+            Console.WriteLine($"Subject: My state has just changed to: {this.State}");
+            Notify();
+        }
+    }
+}

DesignPatternGuru/Observer/Program.cs

@@ -0,0 +1,25 @@
+using Observer.Observers;
+
+namespace Observer
+{
+    internal class Program
+    {
+        static void Main(string[] args)
+        {
+            var subject = new Subject();
+           
+            var observerA = new ConcreteObserverA();
+            subject.Attach(observerA);
+
+            var observerB = new ConcreteObserverB();
+            subject.Attach(observerB);
+
+            subject.SomeBusinessLogic();
+            subject.SomeBusinessLogic();
+
+            subject.Detach(observerB);
+
+            subject.SomeBusinessLogic();
+        }
+    }
+}