Creating A Nested To-Do List in C#

To-Do lists are a great organizational tool that can be made even better when you introduce some categorization abilities. In this example, we'll be taking advantage of the Composite pattern to form a To-Do list that can contain sub-lists and sub-categories!

TodoList Component:

public abstract class TodoList
{
   public abstract void Read(int indent = 0);

   protected virtual string Tab(int indent)
   {
       return new String(' ', indent * 2);
   }
}

ListItem Leaf:

class ListItem: TodoList
{
   string taskDescription;

   public ListItem(string description)
   {
       this.taskDescription = description;
   }

   public override void Read(int indent = 0)
   {
       Console.WriteLine(this.Tab(indent) + this.taskDescription);
   }
}

TaskList Composite:

class TaskList: TodoList
{
   string taskListName;
   List<TodoList> todoList;

   public TaskList(string name)
   {
       this.taskListName = name;
       this.todoList = new List<TodoList>();
   }

   public override void Read(int indent = 0)
   {
       Console.WriteLine(this.Tab(indent) + this.taskListName);
       foreach (TodoList item in this.todoList)
       {
           item.Read(indent + 1);
       }
   }

   public void AddToList(TodoList task)
   {
       todoList.Add(task);
   }

   public  void RemoveFromList(TodoList task)
   {
       todoList.Remove(task);
   }
}

Demo of the Composite Pattern:

public class Solution
{
   public static void Main(string[] args)
   {
       // Top level todo list:
       TaskList todo = new TaskList("To-Do for today:");

       // List for groceries:
       TaskList groceries = new TaskList("Go to the store:");
       groceries.AddToList(new ListItem("Apples"));
       groceries.AddToList(new ListItem("Bread"));
       groceries.AddToList(new ListItem("Yogurt"));
       groceries.AddToList(new ListItem("Popcorn"));

       // Add list to the top level:
       todo.AddToList(groceries);

       // Homework list:
       TaskList homework = new TaskList("Do my homework:");
       homework.AddToList(new ListItem("Math paper"));
       homework.AddToList(new ListItem("Physics quiz"));
       // CS sub-list:
       TaskList csHomework = new TaskList("CSC:");
       csHomework.AddToList(new ListItem("Lab"));
       csHomework.AddToList(new ListItem("Assignment"));
       csHomework.AddToList(new ListItem("Make flashcards"));
       // Add CS list to homework list:
       homework.AddToList(csHomework);
       // Add homework list to top level:
       todo.AddToList(homework);

       // Read off the list:
       todo.Read();

       Console.WriteLine("Done");

       /*
           Output:
           
           To-Do for today:
               Go to the store:
                   Apples
                   Bread
                   Yogurt
                   Popcorn
               Do my homework:
                   Math paper
                   Physics quiz
                   CSC:
                   Lab
                   Assignment
                   Make flashcards
           Done
       */
   }
}