May be I am asking a stupid question here.
I recently noticed an UIApplication delegate method
- (void)applicationSignificantTimeChange:(UIApplication *)application {
}
I was wondering what will be its actual use? Do we need to handle this. Can anyone explain a scenario that can happen in an iOS application and we need to do some coding here.
My App is really sensitive to system time, that is the reason I am asking this question. After seeing this API , I have a feeling that I am missing something here to handle.
I am just curious to know... :)
Thanks,
Ramesh Chandran A
Per the documentation on iOS, this method is called:
Examples of significant time changes include the arrival of midnight,
an update of the time by a carrier, and the change to daylight savings
time. The delegate can implement this method to adjust any object of
the app that displays time or is sensitive to time changes. Prior to
calling this method, the app also posts a
UIApplicationSignificantTimeChange notification to give interested
objects a chance to respond to the change. If your app is currently
suspended, this message is queued until your app returns to the
foreground, at which point it is delivered. If multiple time changes
occur, only the most recent one is delivered.
Examples of when this should be used include:
If your app has repeating scheduled events, such as a local notification that now is past, and your app should reschedule the next notification (like daily reminders).
If your app displays data in time ago that needs to be correct, even if the user sets a bad time (for example a medical app that shows your current glucose reading or similar). If a glucose monitor showed an old glucose value as the users current glucose value for instance, the user could make the wrong decision and get hurt.
How you respond to this event depends on your application. You could for instance, read UTC from a server to see if the phone's UTC is correct within some margin, and take appropriate action, such as warning the user, or updating an internal offset between actual UTC and phone UTC.
Hope that helps.
-applicationSignificantTimeChange: is roughly equivalent to the UIApplicationSignificantTimeChangeNotification notification.
I have a custom date picker control that highlights the today date. Subscribing to this notification allows it to change its highlight at midnight, or if the user messes with the time setting manually.
Related
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.
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.
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
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).
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.
The requirement is that have to detect if the system time of iPhone is changed by user manually. For that I have used
NSNotificationCenter.defaultCenter().addObserver(self, selector: "timeChangedNotification:", name: NSSystemClockDidChangeNotification, object: nil)
and
func timeChangedNotification(notification:NSNotification){
println("Device time has been changed...")
}
But not getting the results.
Also if this time is not changed means it is automatic time provided by network then have to compare with server time.How can this be done? Please give help for the same.
As per its documentation, NSSystemClockDidChangeNotification is:
Posted whenever the system clock is changed. This can be initiated by a call to settimeofday() or the user changing values in the Date and Time Preference panel.
So unless you were expecting the user to change the date or time while your app is running, you're obviously not going to hear anything. Notifications are triggered by events.
iOS doesn't provide you with a way to ask on whose authority the system believes the time and date is the current value — whether it's carrier network time, time server time, user-supplied time or something else. There's no single server time and no way to ask for it. What you want to do cannot be done.
This code worked for me in Swift 3
NotificationCenter.default.addObserver(self, selector: #selector(ClassName.timeChangedNotification), name: NSNotification.Name.NSSystemClockDidChange, object: nil)
}
// Method get called user changed the system time manually.
func timeChangedNotification(notification:NSNotification){
print("Device time has been changed...")
}
I've tried 3 options to do this for an enterprise app that I did that requires the time to always be in sync across users. Since we have no control over the users' setting of the device time, I was also face with your predicament:
Option 1 - Using GPS time: I tried getting the GPS timestamp and comparing it with the local device time. It worked in some countries but did not work in others. Other countries return the device time for some reason.
Option 2 - Using a background process to estimate the approximate time. What you do is to get the timestamp, whenever your app goes to the background. Run a timer that fires every 5 minutes (+/- depending on your tolerance). Then calculate the estimated time by adding the 5min ticks that went by to the stored timestamp when your app becomes active. However, this approach can only detect if the time was changed while your app is already running. And not if the time was changed before your app even started.
Option 3 - Using a time-check at the backend. And this is what I ended up doing. I have a small php backend program that returns the UTC time. So every time my app is executed or returns to the foreground, my app will quickly check the time against my time-server. To handle offline cases, I store the last timestamp before the system goes to the background so you can at least check if the date/time was back-dated. Then check again with the time-server when the system goes online.
So far it's the third option that worked for me. But I guess combining 2 and 3 would even make the system more pull-proof.
It's been a while but it might be useful for anyone who will find this question in future like I did today.
You also could use NTP protocol to know real epoch time at the moment when your app enters background / foreground or in didFinishLaunching. This requires the app to be online, though. But it could help in most cases.
There are at least two open-source libraries for iOS and for Android that can help: TrueTime and Kronos.
In my app I'm registering a NSSystemClockDidChangeNotification notification in AppDelegate method application:application didFinishLaunchingWithOptions:options.
Posted whenever the system clock is changed. This can be initiated by
a call to settimeofday() or the user changing values in the Date and
Time Preference panel. The notification object is null. This
notification does not contain a userInfo dictionary.
Month ago it was working fine, but these days every time I suspend my app, lock my iPhone and leave it 2 minutes to pass, when opening the app, the selector method is called, which is weird to me. I didn't change the system or time, I just let the device idle.
Can anyone help me understand this? I just want to execute some code when the user manually change the system time, just in that case (tried with UIApplicationSignificantTimeChangeNotification but that doesn't help).
Like that: Getting iOS system uptime, that doesn't pause when asleep
But remember, this solution will fail sometimes because of out-of-sync when system tries to update time from NTP server when the Internet connection is not reachable.
This answer is a bit late but this is what the apple support team replied when I ask a similar question:
Part of the question I asked:
Could it be possible for the OS posted [this notification] if the
time/timezone has not changed in the device?
The answer I got from them:
Absolutely [1]. It's common for a notification like this to be posted
redundantly. In some cases it's triggered by a state change you can't
see. For example — and I haven't tested this theory, so it's just an
example of how this sort of thing can come about — this notification
might be posted if the system's giant list of time zone info has
changed. So, the time zone state has changed, but it's not something
that affects your app.
But in other cases, a notification might be truly redundant (-: iOS
is a complex system and in some cases this complex machinery generates
redundant notifications, and there's no need to filter them out
because…
Your app should respond to such notifications be refetching the info
it cares about and updating its state based on that. If this update
is expensive, keep your own copy of the previous state, compare the
current system state to that, and only do the update if the stuff you
care about has actually changed.
I need a piece of code for Xcode (obj-c) that runs every day at 00:00.
The reason for this is because my server updates data each new day and I would like my app to synchronize with the update.
I was thinking about doing a timer that runs every minute and checks the time (from internet, not the phones time), but it seems like there could be an more efficient way.
Help or pointers really appreciated!
Thanks
Use the calendar app on your mac. Set up a recurring event every day at 0:00. At the point where you pick the type of alert, you can select an option to open a file (as opposed to a pop-up, etc.). Pick your app as the file to be opened.
When the app becomes active, register a local notification (UILocalNotification) to trigger at midnight.
Then, you can perform the updates at the app delegate's -application:didReceiveLocalNotification:
You can then cancel the notification when the application goes to background by calling the UIApplication's method -cancelLocalNotification:
I don't think it's even required to use notification here. Notification is usually on best effort basis and doesn't guarantee the delivery. This can be done in few simple steps.
Save the lastUpdated time in your iOS app. Probably in NSUserDefaults or if you're using local database you can store it there as well.
Everytime user launches the application check how much time has elapsed since last update.
If it's more than 24 hours then make an API call to your server and check if there's any new updates available (which you can determine probably from server timestamp). Get the latest data (possibly only the delta difference in stead of everything).
Update the lastUpdated time in your iOS app.
In an iOS app, is there any method to get notified either user changed the date or time setting.
Actually in an app we want to know the time difference between the two app sessions. It can be done by saving the time when user closed the app and when user restart again. But what if user change the time setting in between.
Can we get noticed at the starting of the game whether user changed the time/date setting.
Any suggestions would be of great help.
UIApplicationSignificantTimeChangeNotification is what you're looking for. But there's another case where date may change, for example when user changes time zone. In this case you need to observe NSSystemTimeZoneDidChangeNotification.
I believe that this is what applicationSignificantTimeChange: (on the app delegate) and the UIApplicationSignificantTimeChangeNotification notification is used for (though the case where the user manually changes their time is not listed as an example)