Lecture No. 11

Dated: 21-05-2025

Extension Methods

using System;
using System.IO; // Required for File operations

namespace FileHandlingArticleApp {
    class Program {
        static void Main(string[] args) {
            string filePath = "test.txt"; // Define the file path once for clarity

            // Check if the file exists and display its current content
            if (File.Exists(filePath)) {
                string content = File.ReadAllText(filePath);
                Console.WriteLine("Current content of file:");
                Console.WriteLine(content);
            }

            Console.WriteLine("Please enter new content for the file - type 'exit' and press enter to finish editing:");

            string newContent;
            // Loop to continuously append new lines until the user types "exit"
            while ((newContent = Console.ReadLine()) != "exit") { // Read user input and assign to newContent
                // Append the new content followed by a new line to the file
                File.AppendAllText(filePath, newContent + Environment.NewLine);
            }

            Console.WriteLine("File editing finished. Press any key to exit.");
            Console.ReadKey(); // Keep the console window open
        }
    }
}

using System;
using System.IO; // Required for StreamWriter

class Program {
    static void Main(string[] args) {
        Console.WriteLine("Please enter new content for the file - type 'exit' and press enter to finish");

        // Use a 'using' statement to ensure the StreamWriter is properly closed and disposed of,
        // even if an error occurs. By default, StreamWriter will overwrite the file.
        // If you want to append, you need to use: new StreamWriter("test.txt", true)
        using (StreamWriter sw = new StreamWriter("test.txt")) {
            string newContent = Console.ReadLine(); // Read the first line of input
            while (newContent != "exit") {
                sw.WriteLine(newContent); // Write the content and automatically add a newline
                newContent = Console.ReadLine(); // Read the next line of input
            }
        }

        Console.WriteLine("Content written to test.txt. Press any key to exit.");
        Console.ReadKey(); // Keep the console window open
    }
}

Deleting a File

using System;
using System.IO; // Required for StreamWriter

class Program {
    static void Main(string[] args) {
        Console.WriteLine("Please enter new content for the file - type 'exit' and press enter to finish");

        // The 'using' statement ensures the StreamWriter is properly closed and disposed of,
        // even if an error occurs.
        // By default, `new StreamWriter("test.txt")` will **overwrite** the file if it exists.
        // If you intend to **append** to the file, use `new StreamWriter("test.txt", true)`.
        using (StreamWriter sw = new StreamWriter("test.txt")) {
            string newContent = Console.ReadLine(); // Read the first line of input from the user
            while (newContent != "exit") { // Continue reading until the user types "exit"
                sw.WriteLine(newContent); // Write the user's input to the file, followed by a new line
                newContent = Console.ReadLine(); // Read the next line of input
            }
        }

        Console.WriteLine("Content successfully written to 'test.txt'.");
        Console.WriteLine("Press any key to exit.");
        Console.ReadKey(); // Keeps the console window open until a key is pressed
    }
}

Rename a File

if (File.Exists("test.txt")) {
    Console.WriteLine("Please enter a new name for this file:");
    string newfilename = Console.ReadLine();
    if (newfilename != string.Empty) {
        File.Move("test.txt", newfilename);
        if (File.Exists(newfilename)) {
            Console.WriteLine("The file was renamed to " + newfilename);
            Console.ReadKey();
        }
    }
}

Rename a Directory

if (Directory.Exists("testdir")) {
    Console.WriteLine("Please enter a new name for this directory:");
    string newdirname = Console.ReadLine();
    if (newdirname != string.Empty) {
        Directory.Move("testdir", newdirname);
        if (Directory.Exists(newdirname)) {
            Console.WriteLine("The directory was renamed to " + newdirname);
            Console.ReadKey();
        }
    }
}

Create a Directory

Console.WriteLine("Please enter a name for the new directory:");
string newdirname = Console.ReadLine();
if (newdirname != string.Empty) {
    Directory.CreateDirectory(newdirname);
    if (Directory.Exists(newdirname)) {
        Console.WriteLine("The directory was created!");
        Console.ReadKey();
    }
}

File Info Object

A file info object gives you information about an object.

static void Main(string[] args) {
    FileInfo fi = new FileInfo(System.Reflection.Assembly.GetExecutingAssembly().Location);
    if (fi != null) {
        Console.WriteLine(string.Format("Information about file: {0}, {1} bytes, last modified on {2}",
            fi.Name, fi.Length, fi.LastWriteTime));
        Console.ReadKey();
    }
}

Directory Info Object

A directory info object gives you information about a directory.

DirectoryInfo di = new DirectoryInfo(Path.GetDirectoryName(System.Reflection.Assembly.GetExecutingAssembly().Location));
if (di != null) {
    FileInfo[] subfiles = di.GetFiles();
    if (subfiles.Length > 0) {
        Console.WriteLine("Files:");
        foreach (FileInfo subfile in subfiles) {
            Console.WriteLine("" + subfile.Name + " (" + subfile.Length + " bytes)");
        }
    }
    Console.ReadKey();
}

Listing Subdirectories

DirectoryInfo[] subdirs = di.GetDirectories();
if (subdirs.Length > 0) {
    Console.WriteLine("Directories:");
    foreach (DirectoryInfo subdir in subdirs) {
        Console.WriteLine("" + subdir.Name);
    }
}

Example

We will now build a complete profile save load system with reflection.

using System;
using System.IO;
using System.Reflection;

class Program {
    public class Person {
        public void Load() {
            if (File.Exists("settings.dat")) {
                Type type = this.GetType();
                string propertyname, value;
                string[] temp;
                char[] splitchars = new char[] { '|' };
                PropertyInfo propertyinfo;
                string[] settings = File.ReadAllLines("settings.dat");
                foreach (string s in settings) {
                    temp = s.Split(splitchars);
                    if (temp.Length == 2) {
                        propertyname = temp[0];
                        value = temp[1];
                        propertyinfo = type.GetProperty(propertyname);
                        if (propertyinfo != null)
                            this.SetProperty(propertyinfo, value);
                    }
                }
            }
        }

        public void Save() {
            Type type = this.GetType();
            PropertyInfo[] properties = type.GetProperties();
            TextWriter tw = new StreamWriter("settings.dat");
            foreach (PropertyInfo propertyinfo in properties)
                tw.WriteLine(propertyinfo.Name + "|" + propertyinfo.GetValue(this, null));
            tw.Close();
        }

        public void SetProperty(PropertyInfo propertyinfo, object value) {
            switch (propertyinfo.PropertyType.Name) {
                case "Int32":
                    propertyinfo.SetValue(this, Convert.ToInt32(value), null);
                    break;
                case "String":
                    propertyinfo.SetValue(this, value.ToString(), null);
                    break;
            }
        }

        public int Age { get; set; }
        public string Name { get; set; }
    }

    static void Main(string[] args) {
        Person person = new Person();
        person.Load();
        if ((person.Age > 0) && (person.Name != string.Empty)) {
            Console.WriteLine("Hi " + person.Name + " - you are " + person.Age + " years old!");
        } else {
            Console.WriteLine("I don't seem to know much about you. Please enter the following information:");
            Type type = typeof(Person);
            PropertyInfo[] properties = type.GetProperties();
            foreach (PropertyInfo propertyinfo in properties) {
                Console.WriteLine(propertyinfo.Name + ":");
                person.SetProperty(propertyinfo, Console.ReadLine());
            }
            person.Save();
            Console.WriteLine("Thank you! I have saved your information for next time.");
        }
        Console.ReadKey();
    }
}