I am trying to decide If I need to write a data field or a watch app, but I'vedifficulties to clearly understand the difference ? can someone help me or clarify these ?
This is what's available to data fields (once per second). It's all information that's already been processed, filtered and interpreted for you, like speed, heart rate or cadence https://developer.garmin.com/downloa...vity/Info.html
The choice of built-in activity does change certain things (like whether GPS is on or off by default), but for the most part, data fields have the same capabilities no matter what activity you launch them from. As a matter of fact, a CIQ data field can do some things native data fields can't/won't, like display power in a run activity, or lap count in a strength activity. OTOH, a CIQ data field can't even display the time more frequently than once per second, which a native data field can easily do.
As Jim alluded to, if you want frequent, direct access to sensors, you need to write a device app.
Bottom line, if you can get away with the limitations of a data field, definitely go with a data field.
If a data field is too limiting (hardware acccess, memory limitations, etc) try to change your requirements and go with a data field.
If neither of those options work, and you have lots of time and patience, go with an app. Once you've spent a lot of time with CIQ, apps aren't that bad. But depending on the app, you are going to have to reinvent a lot of what standard activities do for you. And in some cases, you might not even be able to. You lose a lot of built in functionality when you go with an app, like courses, access to the standard menus (and thus things like sensor configuration), assuming your device even supports maps you'll lose most of the customization of showing maps, etc.
