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Posted 16 Dec 2005
Licenced Apache

DayPilot - Building an Outlook-Like Calendar Component for ASP.NET

, 9 May 2016
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A good-looking ASP.NET control that shows events visually arranged in a day calendar. Includes design-time support and data binding.


See also the follow-up articles:

These articles introduce a new DayPilot version for ASP.NET MVC which supports drag & drop AJAX operations (event moving, resizing, and creating).

HTML5/JavaScript Version

DayPilot Lite is also available for HTML5/JavaScript:

The latest release includes AngularJS event calendar [] plugin.

Building an Outlook-Like Calendar Component for ASP.NET

The story is simple and you might have already heard it: I needed a component and because I wasn't able to find a good one I decided to write it. I was thinking like this: It would take me two hours to find it, another two hours to understand it and another two hours to customize it. Six hours. In six hours, I should be able to write a simple component by myself.


  • Reusable ASP.NET component for showing the events in day/week/work week views.
  • HTML5 support
  • Full CSS-based styling.
  • Supports all modern browsers (Chrome, Firefox, Internet Explorer, Edge, Safari, Opera).
  • Visual Studio 2010/2012/2013/2015
  • Azure support
  • Internationalization support (automatic date and time formatting, 12/24 clock support).
  • Accepts data in many forms, including a DataTable, List, and other collections of custom objects.
  • Support for database backends (Microsoft SQL Server, MySQL, etc.)
  • Simple mapping of data object fields (DataStartField, DataEndField, DataIdField, DataTextField).
  • User-defined JavaScript/server-side action for clicking the event.
  • User-defined JavaScript/server-side action for clicking the free time.
  • Support for business hours - doesn't show the time outside the working hours unless there is an event.
  • Support for events started before or finish after the current day.
  • Support for overlapping events (two or more events for a particular moment).
  • Commercial-friendly open-source license (Apache Software License 2.0)

Algorithm for Arranging Concurrent Events

The following mechanism is used to arrange the events:

  • "Event" class will keep the basic information about the event, like starting and ending time, title, etc.
  • "Day" class will keep all the events for a certain day. It will be able to load the events from a DataTable. Each day can contain zero or more Blocks.
  • "Block" class will contain events that overlap with one another. Each Block contains one or more Columns.
  • "Column" class will contain all the events inside a Block that can be in a single Column.

Let's demonstrate it visually:

The algorithm can be described in the following steps:

  1. Shorten all the Events so that they don't overlap to another day (e.g. if something starts yesterday, let's make it start today at 00:00).
  2. Extend the Events' duration to 30 minutes blocks (we would have problems showing a duration of 5 minutes, 5 seconds - it wouldn't be possible to write any text into a rectangle of such a small height).
  3. Find Blocks:
    • Order all the events by the starting time (primary) and by the ending time in reverse (secondary) - longer events go closer to the left.
    • Iterate through the events - if it overlaps with the previous add it to the current Block; otherwise create a new Block.
  4. Arrange Events into Columns inside a Block (do this for each Block):
    • Find a moment with the most overlaps and count the overlaps. Create that many numbers of Columns.
    • Arrange Events into Columns - find the first free Column from the left and place it there.

Now, we can calculate the position of each Event because we know the Blocks and Columns:

  • Left: (the column number)/(total count of columns for the owner block) in percent.
  • Width: 1/(total count of columns) in percent
  • Top: (starting time)*(hour height)
  • Height: (duration)*(hour height)

Quick-Start Example

ASP.NET Control Declaration (.aspx)

<DayPilot:DayPilotCalendar ID="DayPilotCalendar1" runat="server" 

Loading data (.aspx.cs)

protected void Page_Load(object sender, EventArgs e)
  if (!IsPostBack)
      DayPilotCalendar1.StartDate = firstDayOfWeek(DateTime.Now, DayOfWeek.Sunday);
      DayPilotCalendar1.DataSource = getData();

More information about event loading [].

See also the DayPilot Tutorial for a step-by-step setup guide.

Scheduler (3.0)

DayPilot Lite 3.0 supports Scheduler ASP.NET control that allows you to display a scheduler for multiple resources side-by-side.

See also:

Gantt Chart (3.2)

DayPilot Lite 3.2 supports Gantt Chart ASP.NET control (displaying one task per line).

See also:

CSS Theme Styling (4.0)

DayPilot Lite 4.0 supports full calendar and scheduler CSS styling.

You can design your own CSS theme in the online theme designer:

Built-In CSS Theme (4.1)

DayPilot Lite 4.1 includes a built-in CSS theme. The CssOnly mode (full calendar CSS styling mode) is now enabled by default. The calendar default CSS theme can be displayed without any external dependencies.

Drag and Drop (5.0)

DayPilot Lite for ASP.NET WebForms 5.0 [] now supports calendar drag and drop:

  • event moving
  • event resizing
  • time range selecting

Source and binary available for download [].

NuGet Package

DayPilot Lite is also available as a NuGet package:



This article, along with any associated source code and files, is licensed under The Apache License, Version 2.0


About the Author

Dan Letecky
Czech Republic Czech Republic

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Comments and Discussions

GeneralExtracting Pin
ClaudeX7-Jun-07 0:40
memberClaudeX7-Jun-07 0:40 
GeneralRe: Extracting Pin
Dan Letecky8-Jun-07 22:56
memberDan Letecky8-Jun-07 22:56 

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