I did lots of google search but haven't found any solotions that match my need. So I came up with my own solutions but not sure if it's feasible or not. I need to monitor more than 20 regions. So at the first time, I'll start monitoring the current user's location and I get 19 other available locations that I can monitor, let say the radius to monitor is 100 meters. So right now the delegate didEnterRegion should be called? I don't really care about this. But when user moves more than 100m from original location, delegate didExitLocation will be called, and by this time, I'll update new regions to monitor (by sending new current's user location to server and I'll get list of new regions to monitor), and I will still monitor this new user's location and still get 19 other regions that I can monitor. Is this solution feasible? Have anyone tried? Does this solution still work if the app is suspended, and if it consumes lots of battery?
This is actually Apple's suggestion Core Location Programming Guide:
To work around this limit, consider registering only those regions in the user’s immediate vicinity. As the user’s location changes, you can remove regions that are now farther way and add regions coming up on the user’s path.
However, it's not clear how much time you get when didEnterRegion: is called in the background, so it's not clear if you have time to make a server call if running the background. The "significant-change location service" information says:
If you leave the significant-change location service running and your iOS app is subsequently suspended or terminated, the service automatically wakes up your app when new location data arrives. At wake-up time, the app is put into the background and you are given a small amount of time (around 10 seconds) to manually restart location services and process the location data.... Because your app is in the background, it must do minimal work and avoid any tasks (such as querying the network) that might prevent it from returning before the allocated time expires. If it does not, your app will be terminated. If an iOS app needs more time to process the location data, it can request more background execution time using the
beginBackgroundTaskWithName:expirationHandler:method of the UIApplication class.
You could try the combination of region monitoring, making a server call in didEnterEter region and then calling beginBackgroundTaskWithName:expirationHandler: to make sure you have enough time. The combination of region monitoring + server calls + background processing is going to hit battery life, though.
EDIT: You could also create "mega regions" of a large area that contain many smaller regions. When the user enters those mega regions, set up and add all the smaller regions you are interested in, and when they exit, remove them.