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Implementing the Liskov Substitution Principle

Understand how to apply the Liskov Substitution Principle in C# by analyzing a text processing example. Learn to adjust class inheritance and method overriding to avoid unexpected behavior, ensuring your derived classes maintain base class functionality without breaking existing code. This lesson guides you through practical steps to adhere to SOLID principles while enhancing software design.

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We have the following console application that reads the textual content of a file, encloses every paragraph in the p HTML tags, and makes conversion of specific Markdown markers into equivalent HTML tags.

Note: Run the following code. The program will ask for the file to convert. Enter sample.txt as the name of the file. When the program stops execution, press any key to return to the terminal. Now, enter the cat sample.html command to see the content after conversion.

using System.Text;
using System.Text.RegularExpressions;

namespace TextToHtmlConvertor;

public class TextProcessor
{
   public virtual string ConvertText(string inputText)
   {
       var paragraphs = Regex.Split(inputText, @"(\r\n?|\n)").Where(p => p.Any(char.IsLetterOrDigit));
       var sb = new StringBuilder();
        foreach (var paragraph in paragraphs)
        {
            if (paragraph.Length == 0)
            {
                continue;
            }
            sb.AppendLine($"<p>{paragraph}</p>");
        }
        sb.AppendLine("<br/>");
        return sb.ToString();
   }
}
Implementing the Liskov substitution principle

We have the TextProcesor.cs file with the following content:

C#
using System.Text;
using System.Text.RegularExpressions;
namespace TextToHtmlConvertor;
public class TextProcessor
{
    public virtual string ConvertText(string inputText) 
    {
        var paragraphs = Regex.Split(inputText, @"(\r\n?|\n)").Where(p => p.Any(char.IsLetterOrDigit));
        var sb = new StringBuilder();
        foreach (var paragraph in paragraphs)
        {
            if (paragraph.Length == 0)
            {
                continue;
            }
            sb.AppendLine($"<p>{paragraph}</p>");
        }
        sb.AppendLine("<br/>");
        return sb.ToString(); 
    }
}

We also have a class that derives from it, which is called the MdTextProcessor class. It overrides the ConvertText method, written on lines ...