Generate iCalendar feed from ASP.NET

In order to feed calendar clients (like MS Outlook, Google Calendar) it is required to supply a plain text file with the ‘.ics’ extension.

BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//WPCS/iManagement//..//EN
BEGIN:VEVENT
UID:7264
DTSTAMP:20090917T152000Z
SUMMARY:(16:00-17:00)iFinance pilot - kick off
CLASS:PUBLIC
DESCRIPTION:kick off meeting
CATEGORIES:IMANAGEMENT - PROJECTS
LOCATION:
STATUS:CONFIRMED
PRIORITY:1
DTSTART:20090917T160000
DTEND:20090917T170000
TRANSP:OPAQUE
END:VEVENT
END:VCALENDAR

One approach is to generate the iCalendar data using the code behind of a regular .aspx page. The key part in this case is to inform the ASP processor how to handle the page: instead of displaying just text, will pass it off to the operating system. These two lines can be placed in the Page_Load event:

Response.AddHeader("content-disposition", "attachment; filename=WorkAheadFeed.ics");
Response.ContentType = "text/calendar;method=request;charset=UTF-8;component=vevent";

As an alternative – if the performance is an issue – one can use a WebHandler (.ashx file), being known that the output is not intended for a browser.
In this case will have to include the IsReusable property and place the code behind logic in the ProcessRequest() which will be invoked whenever the file is requested.

A simple feed will look like this:

   DateTime datStart = DateTime.Now.AddDays(5);
   DateTime datEnd = datStart.AddMinutes(60);
   string strLocation = "Big office";
   string strSummary = "(16:00-17:00)iFinance pilot - kick off";
   string strDescription = "kick off meeting";
 
	public static string GetFormatedDate(DateTime date)
	{
		return date.ToString("yyyyMMdd");
	}
	public static string GetFormattedTime(DateTime date, bool bUTC)
	{
		return date.ToString("HHmm") + (bUTC ? "00Z" : "00");
	}
   Response.Write("BEGIN:VCALENDAR");
   Response.Write("\nVERSION:2.0");
   Response.Write("\nPRODID:-//WPCS/iManagement//..//EN");
   Response.Write("\nBEGIN:VEVENT");
   Response.Write("\nUID:7264");
   Response.Write("\nDTSTAMP:" + GetFormatedDate(DateTime.Now) + "T" + GetFormattedTime(DateTime.Now, true));
   Response.Write("\nSUMMARY:" + strSummary);
   Response.Write("\nCLASS:PUBLIC");
   Response.Write("\nDESCRIPTION:" + strDescription);
   Response.Write("\nCATEGORIES:IMANAGEMENT - PROJECTS");
   Response.Write("\nLOCATION:" + strLocation);
   Response.Write("\nSTATUS:CONFIRMED");
   Response.Write("\nPRIORITY:1");
   Response.Write("\nDTSTART:" + GetFormatedDate(datStart) + "T" + GetFormattedTime(datStart, false)));
   Response.Write("\nDTEND:" + GetFormatedDate(datEnd) + "T" + GetFormattedTime(datEnd, false)));
   Response.Write("\nTRANSP:OPAQUE");
   Response.Write("\nEND:VEVENT");
   Response.Write("\nEND:VCALENDAR");

For complete iCalendar specification see following:

iCalendar Specification Excerpts
Internet Calendaring and Scheduling Core Object Specification

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