What kind of data structure to use when working with calendar items?

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.NET2.0

.NET

algorithm

Hi, I am working on a calendar project using .NET framework and is running into a horrible performance issue when working with dates. The issue is that whenever I want to retrieve all the events and to-dos occurring on a particular date, I have to transverse the entire list of events and to-dos checking which events and/or to-dos occur on that date. The problem gets worse when I work with project tasks as well. Thus, it is 3 O(n).

Typically, in this kind of situation, I would use a sorted binary tree data structure as storage rather than a list, but I don't know how to sort them when recurrence occurs. Thus, I need some recommendation on how I can improve the performance for retrieving all items occurring on a particular date. Also, this data structure must be able to handle situation when events' and/or to-dos' date is changed.

It is kind of hard to show just only relevant details about the project without overwhelming this question with details, but I will give it a try. I am integrating currently four different components together:
- MonthCalendar class library
- DDay.iCal class library for using iCal file
- Microsoft Office Project 12.0 Object Library
- Plug-In Framework

Microsoft Office Project 12.0 Object Library will be applied via one of the plug-ins. What is events, to-dos, and recurrence is explained in details on this standard. A simple and short version summary can be found on Wikipedia.

Using the event handler, every time I select a date on MonthCalendar, execute the following:

private void calendar_DaySelected(object sender, DaySelectedEventArgs e)
        {
            DateTime date = DateTime.Parse(e.Days[0]);

            schedulePanel.EventList.Clear();
            schedulePanel.EventList.AddRange(calendarPanel.Calendar.GetDateInfo(date));

            schedulePanel.TodoList.Clear();
            schedulePanel.TodoList.AddRange(todoPanel.GetDateInfo(date));

            if (projectPlugins.Count > 0)
            {
                schedulePanel.Tasks.Clear();
                for (int i = 0; i < projectPlugins.Count; i++)
                {
                    schedulePanel.Tasks.AddRange(projectPlugins[i].GetDateInfo(date));
                }
            }

            schedulePanel.Update(date);
        }

Here is the partial class code for SchedulePanel:

public SchedulePanel()
        {
            InitializeComponent();
            eventList = new List<Library.DateItem>();
            taskList = new List<PluginSDK.ITask>();
            todoList = new List<ITodo>();
        }
        public void Update(DateTime date)
        {
            Text = "Schedule for " + date.ToShortDateString();
            eventGridView.Rows.Clear();
            //Display Occurring Events
            for (int i = 0; i < eventList.Count; i++)
            {
                eventGridView.Rows.Add();
                eventGridView.Rows[i].Cells[0].Value = eventList[i].Event.Summary;
            }
            //Display Occurring Project Tasks
            if (taskList.Count != 0)
            {
                if (!this.Controls.Contains(this.taskBox))
                {
                    this.Controls.Add(this.taskBox);
                    this.todoBox.Location = new System.Drawing.Point(3, 232);
                    this.todoBox.Size = new System.Drawing.Size(193, 116);
                }
                taskListBox.Items.Clear();
                for (int j = 0; j < taskList.Count; j++)
                {
                    taskListBox.Items.Add(taskList[j].Name);
                }
            }
            else
            {
                if (this.Controls.Contains(this.taskBox))
                {
                    this.Controls.Remove(this.taskBox);
                    this.todoBox.Location = new System.Drawing.Point(3, 103);
                    this.todoBox.Size = new System.Drawing.Size(193, 236);
                }
            }
            //Display Occurring To-dos
            todoListBox.Items.Clear();
            for (int i = 0; i < todoList.Count; i++)
            {
                todoListBox.Items.Add(todoList[i].Summary);
            }
        }
        public List<Library.DateItem> EventList
        {
            get
            {
                return eventList;
            }
        }
        public List<ITodo> TodoList
        {
            get
            {
                return todoList;
            }
        }
        public List<PluginSDK.ITask> Tasks
        {
            get
            {
                return taskList;
            }
        }

Here is the partial class code for TodoPanel:

public List<ITodo> GetDateInfo(DateTime date)
        {
            List<ITodo> todos = new List<ITodo>();
            for (int i = 0; i < todoList.Count; i++)
            {
                if (todoList[i].Status != TodoStatus.Completed)
                {
                    if (todoList[i].Start != null && todoList[i].Start.Date <= date)
                        todos.Add(todoList[i]);
                    else if (todoList[i].Due != null && todoList[i].Due.Date <= date)
                        todos.Add(todoList[i]);
                }
            }
            return todos;
        }

Here is the partial class code for MSProjectPanel using Microsoft Office Project 12.0 Object Library:

public List<ITask> GetDateInfo(DateTime date)
        {
            List<ITask> tasks = new List<ITask>();
            foreach (Project project in application.Projects)
            {
                foreach (Task task in project.Tasks)
                {
                    if (task.OutlineChildren.Count == 0 && task.Status != PjStatusType.pjComplete)
                    {
                        if (CompletePrerequisite(task) && DateTime.Parse(task.Start.ToString()) <= date)
                        {
                            tasks.Add(new ProjectTask(task));
                        }
                    }
                }
            }
            return tasks;
        }

It takes about 3+ seconds to finish executing after selecting a new date on 2.16GHz computer running Microsoft XP Professional with 512 MB of RAM. Currently, I am using 3 iCal files and 2 MPP files. That should be about 150+ items (events, to-dos, and 100+ project tasks) combined. Without MSProject plugin, it drops down to 1+ second.