I try to develop an 'add this event to your agenda' feature on a mobile website. I found some entries about that but none of them works for me.
How to add .vcs file to Android Calendar
Add Calendar event to Android from web .vcs download
I can't asking for my users to download an app if they want to open this file.
I've made several tests, on Nexus 4 (4.4.2) and Nexus 5 (4.4.4) neither ical or vcal files work. Files are downloaded, but I can't open them. The behavior is different on Samsung devices. On S2(4.0.3) only vcal format works. It starts an 'Agenda' activity. On S4 mini (4.2.2), iCal and vCal files are handled by 'S Planner'.
Any Ideas ?
How to create a calendar event (ics or vcs) on a website that'll be handled by Android?
Android is an operating system. It does not handle calendar event files -- calendar apps do. As you have discovered, there are many calendar apps for Android, and a user may have zero, one, or several of them installed. Some may offer support for calendar event files, some may not.
This is no different than Windows or Linux, where the OS does not handle calendar event files, and whether or not the user has a program installed that does is up to the user.
I can't asking for my users to download an app if they want to open this file.
Then do not "develop an 'add this event to your agenda' feature on a mobile website". There is no requirement that any user visiting your site must have pre-installed a calendar app that happens to meet your specifications.