I am currently saving locations in background. I need latitude, longitude and NSDate which is why I went with CLLocation instead of geopoint. I am trying to figure out how to save locations only every minute or so, as I currently have one element each second.
I cannot use NSTimer as my app still needs to obtain these updates after the authorised delay of running code when in background.
Any suggestion of how this might be done ?
Thank you very much in advance for your help.
Viktor
Make sure you read: Getting the User’s Location,
there are important notes about battery life.
IMO it's better to rely on the framework callbacks and not try to put a timer on it.
You may also consider region monitoring..
Maybe you can give us more details about what you're trying to achieve.
Related
I have an IOS app where I require the user's current location in order to make an HTTP request to get data about nearby locations. Since I just need the user's location once, I am using the CoreLocation requestLocation method. This issue with this is that it takes roughly 10 seconds (which is stated in the documentation). I realize that there will always be a delay which I am prepared for, but the delay on requestLocation is just too long and ruins the user experience.
I was wondering if anyone has thought of a way to get the users location (just once) in a more timely way.
One solution I thought of was perhaps calling the method within the AppDelegate, as the app starts, and then passing the data to the ViewControllers via some shared object. The issue I foresee here is that AppDelegate does complete it's application:didFinishLaunchingWithOptions: function very quickly so I don't think it'll improve my problem
Another solution I thought of could be to use the startUpdatingLocation method, and then use stopUpdatingLocation after receiving the first location. My issue with this is that startUpdatingLocation may also take a few seconds to start up (documentation), so again this may not improve my problem.
The location I get for the user does not need to be super accurate so I am willing to compromise on precision for performance.
This question already has an answer here:
Update location in Background
(1 answer)
Closed 4 years ago.
I'm making a location tracking app. In this app, I need to record user location every 10 seconds. Also, the recording is done in a background service so that the application does not need to be in foreground. To make this, I tried to use Timer but it's not working in background. I've tried so much but it didn't work. Could you help me please?
I found this great tutorial: https://www.raywenderlich.com/5817-background-modes-tutorial-getting-started
I had a similar app to be built some time ago, and I also tried things like you did, but that is very very wrong way to use timer and all to record your location.
First of all, I suggest you to not try to record/ping location explicitly because, it will cause batter drainage. There is something called, significant location change, please go through it in docs. This will trigger you location update in every single significant location change.
But I assume, you really need to ping the location. There is a git repo, link below
Background geo location tracking
Please go though it, it is really nice library out there, I have ever come across, go through its documents. I am sure you will come around and be able to use it for your app. :)
I want my app to have a subscription service and the way I see it is by keeping timeIntervalSince1970 as an "until" date. But that is easily avoidable if the user changes system's current time. Is there any better way to track that in offline mode?
take a look at this post1, it explain how to measure passed time, independent of clock and time zone changes.
you also take a look at this post2, it explain how detect device time change only when it is changed manually
Let me know if this helps you :)
I have a problem in Objective C (writing an app for the iPhone). I know how to use the locationManager and its delegates. Once I called startUpdatingLocation on the locationManager, it will call the delegate method didUpdateToLocation whenever the location is updated. But the problem is, that this way is now suitable for what I want to do. I have a method (in a class) which looks as follows:
#implementation SomeClass
- (someType)getDbContentsOrderByDistance
{
... //here I need the current location
return dbContents;
}
#end
Now this function selects entries from a sqlite database ordered by their distance to the users current location. That is why I need the location in this function. What I want to do in the above method is: get the location, then select the stuff from the database and return it. I know that I could just try to access locationManager.location.coordinate.longitude, but I know that there won't be anything useful inside until the first location update has arrived. And I don't want to start the location updates before (e.g. when starting the app) because that would not be very efficient if I only need the location once.
I know how to do it the way that the delegate is called as soon as a location update arrives. The problem is that I don't know how to get that updated location from there into my method above. Basically I would need to let the method 'wait' until there is the first location update and then continue execution with that location.
Thank you for your help!
The short answer is, you can't. Getting the users location is an asynchronous process, and MUST be an asynchronous process. The device has to fire up various hardware like the GPS, cell tower locator, and WiFi triangulation system, get input from those different devices, and synthesize that into a location. That takes multiple seconds to do.
Putz's suggestion of starting a timer is a good one. I would add a few things however.
Typically the first readings you get from the location manager are really bad and should be discarded. The first reading you get is usually the last location reading when the GPS was active, and will have an out-of-date timestamp. The accuracy reading in that location might appear quite good, but it's a lie. I have seen the first location reading be off by several kilometers. You need to check the timestamp on your location updates and discard any reading that is more than 1 second old.
Once you've discarded the stale readings, the first several location updates are often really bad because the GPS hasn't settled down yet. The horizontal accuracy reading (which is really a "circle of confusion", or radius of possible positions) is an absurdly large value, sometimes a kilometer or more. Again, you need to write your location manager delegate method to discard readings that are too inaccurate. I suggest discarding values with a horizontal accuracy reading of >= 100 meters. How much inaccuracy you can tolerate depends on the specific appellation, but beware of making the accuracy requirement too accurate. Sometimes the GPS refuses to settle down. If you require a 5 meter accuracy, you might not get an acceptable accuracy during the entire run of your app. (If you're in an urban environment, a building, or other area where there is a lot of interference/obstruction of GPS signals)
Once you finally do get a value that's accurate enough, save the location and set your locationAvailable flag to YES.
Note that instead of a timer you could use the notification manager to broadcast a "got a good location" message. Any object that needs location information could register for your notification, and get called when the location manager gets an acceptable location reading.
Start a timer that fires every second or so that calls the function you need the location in. check to see if the location has been set. If the location is valid then kill the timer, if not then let the timer continue and check again in one second or so.
The way of knowing if the location is valid is in the delegate method. Set a global variable like locationAvailable = false. Then when the delegate method gets called set that variable to true.
Using location property can solve the purpose
From apple documentation
location The most recently retrieved user location. (read-only)
#property(readonly, nonatomic, copy) CLLocation *location
The value of this property is nil if no location data has ever been retrieved.
In iOS 4.0 and later, this property may contain a more recent location object at launch time. Specifically, if significant location updates are running and your app is terminated, this property is updated with the most recent location data when your app is relaunched (and you create a new location manager object). This location data may be more recent than the last location event processed by your app.
It is always a good idea to check the timestamp of the location stored in this property. If the receiver is currently gathering location data, but the minimum distance filter is large, the returned location might be relatively old. If it is, you can stop the receiver and start it again to force an update.
Whenever I create a new instance of location manager I get the most recent value of location in location property and since my distance filter is not set , it has the current timestamp. This means I dont have to call startUpdatingLocation and my data is accurate. I also need this for calculating distance between user location and a place so I can immediately return true or false if it is within the range. I find this very useful as I get location within 0.006 seconds and handy and got it from apple documentation only but still I dont know if it is a best practice.
This is stated in CLLocationManager class reference:
When requesting high-accuracy location data, the initial event delivered by the location service may not have the accuracy you requested.
This is really affecting my app. How can I make sure that the location found is the one with the correct accuracy?
I tried to use the 4th or 5th update rather than first retrieved location but this is not a good solution. Any idea?
You should check the accuracy of the updates, CLLocation
contains a property horizontalAccuracy which you can use to check the accuracy.
When the CLLocation has an accuracy that you find accurate enough you use and ignore al others.
Als you should tel CLLocationManager your desired accuracy. To do this set the desiredAccuracy property in CLLocationManager.
I think you will have to live with that. That's how Apple implemented it. Getting a fine grained position takes time, just think about how long any windshield-mounted GPS devices in cars take to fix up their position.
So instead of letting your application wait for a longer time, they provide with what accuracy is available almost immediately, based on cell-towers and WiFi hotspots in the vicinity. Only when there has been a more reliable GPS fix will they call into your app again and let you know.
In the end, it is just a question of where the waiting for the fine-grained position is: In your app, where you have the chance of doing something with the more coarse-grained data you get quickly, or in their framework with no chance for apps to do anything useful in the meantime. I think, letting you decide is the better choice.
Depending on the type of app, you could have a map that automatically zooms in deeper as soon as better position data comes in, draw a smaller circle around the position you are expecting etc. For the end user, nothing's worse than waiting without getting any feedback. So even though this is probably not the answer you would have liked, I advise to make the best of it from a user's perspective.