sample code

MySolution/ConsoleApp/.vscode/launch.json

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+{
+    // Use IntelliSense to learn about possible attributes.
+    // Hover to view descriptions of existing attributes.
+    // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
+    "version": "0.2.0",
+    "configurations": [
+        {
+            "name": ".NET Core Launch (console)",
+            "type": "coreclr",
+            "request": "launch",
+            "preLaunchTask": "build",
+            "program": "${workspaceFolder}/bin/Debug/net7.0/ConsoleApp.dll",
+            "args": [],
+            "cwd": "${workspaceFolder}",
+            "console": "internalConsole",
+            "stopAtEntry": false
+        },
+        {
+            "name": ".NET Core Attach",
+            "type": "coreclr",
+            "request": "attach"
+        }
+    ]
+}

MySolution/ConsoleApp/.vscode/tasks.json

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+{
+    "version": "2.0.0",
+    "tasks": [
+        {
+            "label": "build",
+            "command": "dotnet",
+            "type": "process",
+            "args": [
+                "build",
+                "${workspaceFolder}/ConsoleApp.csproj",
+                "/property:GenerateFullPaths=true",
+                "/consoleloggerparameters:NoSummary"
+            ],
+            "problemMatcher": "$msCompile"
+        },
+        {
+            "label": "publish",
+            "command": "dotnet",
+            "type": "process",
+            "args": [
+                "publish",
+                "${workspaceFolder}/ConsoleApp.csproj",
+                "/property:GenerateFullPaths=true",
+                "/consoleloggerparameters:NoSummary"
+            ],
+            "problemMatcher": "$msCompile"
+        },
+        {
+            "label": "watch",
+            "command": "dotnet",
+            "type": "process",
+            "args": [
+                "watch",
+                "run",
+                "--project",
+                "${workspaceFolder}/ConsoleApp.csproj"
+            ],
+            "problemMatcher": "$msCompile"
+        }
+    ]
+}

MySolution/ConsoleApp/ConsoleApp.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net7.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>

MySolution/ConsoleApp/Program.cs

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+using Samples;
+
+namespace ConsoleApp;
+class Program
+{
+    static void Main(string[] args)
+    {
+        #region Delegate
+        
+        // CalculateSample.Sample();
+        // MessagePrinterSample.Sample();
+            
+        #endregion
+
+
+        #region Callback
+        
+        // StringLength.Sample();
+
+        #endregion
+
+
+        #region Event
+            
+        EventSample.Sample();
+
+        #endregion
+
+    }
+}

MySolution/ConsoleApp/Samples/CalculateSample.cs

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+using System;
+
+namespace Samples
+{
+    class CalculateSample
+    {
+        private delegate int Calculate(int x, int y);
+
+        public static int Add(int x, int y)
+        {
+            return x + y;
+        }
+
+        public static int Subtract(int x, int y)
+        {
+            return x - y;
+        }
+
+        public static void Sample()
+        {
+            Calculate calc1 = Add;
+            Calculate calc2 = Subtract;
+
+            Console.WriteLine(calc1(10, 5));
+            Console.WriteLine(calc2(10, 5));
+        } 
+    }
+}

MySolution/ConsoleApp/Samples/EventSample.cs

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+using System;
+
+namespace Samples
+{
+    public delegate void CustomEventHandler(object sender, EventArgs e);
+
+    class EventSample
+    {
+        public static void Sample()
+        {
+            Button button = new Button();
+            button.Click += new CustomEventHandler(Button_Click);
+
+            button.OnClick();
+        }
+
+        private static void Button_Click(object sender, EventArgs e)
+        {
+            System.Console.WriteLine("Button clicked!");
+        }
+    }
+    
+    class Button
+    {
+        public event CustomEventHandler Click;
+
+        public void OnClick()
+        {
+            if (Click != null)
+                Click(this, EventArgs.Empty);
+        }
+    }
+}

MySolution/ConsoleApp/Samples/MessagePrinterSample.cs

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+using System;
+using System.Diagnostics;
+using System.Threading.Tasks;
+
+namespace Samples
+{
+    class MessagePrinterSample
+    {
+        private delegate Task MessagePrinter(string message);
+
+        private static async Task PrintMessageAsync(string message)
+        {
+            await Task.Delay(1000);
+            Console.WriteLine(message);
+        }
+
+        public static void Sample()
+        {
+            MessagePrinter printer = PrintMessageAsync;
+            Console.WriteLine("Start...");
+            
+            printer("This is first message");
+            printer("This is second message");
+            printer("This is third message");
+            
+            Console.WriteLine("Finish...");
+        }
+    }
+}

MySolution/ConsoleApp/Samples/StringLength.cs

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+using System;
+
+namespace Samples
+{
+    class StringLength
+    {
+        public static void Sample()
+        {
+            string[] words = new string[]
+            {
+                "Apple",
+                "Banana",
+                "Cherry",
+                "Pear",
+            };
+
+            CalculateStringLength(words, PrintStingLength);
+        }
+
+        private static void CalculateStringLength(string[] words, Action<int[]> callback)
+        {
+            int[] lengths = new int[words.Length];
+            for (int i = 0; i < words.Length; i++)
+            {
+                lengths[i] = words[i].Length;
+            }
+
+            if (callback != null)
+                callback(lengths);
+        }
+
+        private static void PrintStingLength(int[] lengths)
+        {
+            foreach (int length in lengths)
+            {
+                Console.WriteLine(length);
+            }
+        }
+    }
+}

MySolution/MySolution.sln

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+
+Microsoft Visual Studio Solution File, Format Version 12.00
+# Visual Studio Version 17
+VisualStudioVersion = 17.0.31903.59
+MinimumVisualStudioVersion = 10.0.40219.1
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "ConsoleApp", "ConsoleApp\ConsoleApp.csproj", "{AF3FAEF8-E438-4E8C-9A99-C0A94649EFEE}"
+EndProject
+Global
+	GlobalSection(SolutionConfigurationPlatforms) = preSolution
+		Debug|Any CPU = Debug|Any CPU
+		Release|Any CPU = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(SolutionProperties) = preSolution
+		HideSolutionNode = FALSE
+	EndGlobalSection
+	GlobalSection(ProjectConfigurationPlatforms) = postSolution
+		{AF3FAEF8-E438-4E8C-9A99-C0A94649EFEE}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{AF3FAEF8-E438-4E8C-9A99-C0A94649EFEE}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{AF3FAEF8-E438-4E8C-9A99-C0A94649EFEE}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{AF3FAEF8-E438-4E8C-9A99-C0A94649EFEE}.Release|Any CPU.Build.0 = Release|Any CPU
+	EndGlobalSection
+EndGlobal