问题
I am looking for solution to get data in background mode even app is terminated. There are lots of tutorials and answers available for this questions, but my questions is different than other. I haven't find any proper solution on stackoverflow, so posted this question.
I have scenario which I can explain. I'm using realm database which store event date, name, time, address etc. Now the thing is that, I want to write a code which are execute in background, In this code I want to get all event data and compare their date with today's date. And based on days remaining between these days fire local notification to remind user about how many days are remaining for specific event.
I want to call this background fetch method exactly 8 AM in local time everyday.
I haven't write any code due to confused with Background fetch and implementation. Can anyone know how to implement this ?
Help will be appreciated.
回答1:
I have got solution to fix issue. As per I have talked,
I want to write a code which are execute in background, In this code I want to get all event data and compare their date with today's date. And based on days remaining between these days fire local notification to remind user about how many days are remaining for specific event.
So, when I getting response from API, I'm creating local notification for all events with unique id, which are fire and repeat daily at specific time, where I have display event time and remaining days of event.
回答2:
Apple documentation states that there is no guarantee when background fetch is performed. It's up to the system to decide.
The system waits until network and power conditions are good, so you should be able to retrieve adequate amounts of data quickly.
The guaranteed way to wake your app is to send at 8 am VoIP push notification from the server. It is guaranteed that the app will be wakened upon receiving a push, and you'll be able to execute the jobs you need. For more details, https://medium.com/ios-expert-series-or-interview-series/voip-push-notifications-using-ios-pushkit-5bc4a8f4d587
回答3:
It is not possible to wake up the app from suspended mode in iOS except with push notification (for this server has to send push notification).
回答4:
This is something which is not documented anywhere. IMHO and experience with iOS, Apple must be recording user activities since the start of the iOS era. ScreenTime is a product of those recordings only that apple was able to create and visualize the data to present a user facing app that very beautifully restricts, manages and displays your activities. In WWDC 2018, it was even quoted that apple will even detect, if the user opens your app at let's say 9 PM daily before going to bed, iOS will allow every possible resource (battery, internet, processing time etc) to that app at 9 PM. But you need to understand your user activities before you do this. Let's take an example of:
News App: A majority of users would check the news in the morning (If they are not instagram addicts). At this time even apple should be biased to open your app with background fetch. Unless of-course there is too much of a resource crunch
A Game: Many games allow provide a restriction time by calling it "recharge" or "re-fill" the energy of a character before user can play another round. This is done so that the addicted person would buy gems to remove that restriction and hence monetize the idea. But if you know that the refill process is completed before 8:00 AM in the morning or user plays your game daily at 8:00 AM configure background fetch accordingly.
Background fetch works with interval rather than specific time.
// Fetch data once an hour.
UIApplication.shared.setMinimumBackgroundFetchInterval(3600)
Lastly why don't you try silent push notifications? Based on your question, I think silent notification is enough to wake your app after a push notification from the server, download some data and do your calculation and provide a local notification.
来源：https://stackoverflow.com/questions/49368922/background-fetch-at-specific-time