it is more helpful if we can get the sample code to implement in our sample project
I suppose you mean reading the HR directly from the device, not getting the HR on the app, am I right? If so, then you can set up your watch to braodcast the HR over ANT+, or on some Garmin models even over BT. It then uses the common standard used by most HRMs - you an google it out easily, or you can use the code from some of OpenSource projects for HRMs.