In the app I'm making I need objects to delete themselves after a certain amount of time in Parse. I'm pretty sure I need an NSTimer but I'm not positive. Is there anyone that could help me?
Thanks
You can do it with NSTimer, but depending on your use case, that may not be ideal.
NSTimer will stop running in the background after a specific amount of time. See: How to run NSTimer in background beyond 180sec in iOS 7?
Futhermore, if your app is not running, you will not be able to do this time based deletion in your Parse database.
What is ideal is to have background jobs running in the Parse cloud. See: http://blog.parse.com/announcements/introducing-background-jobs/
and the Parse documentation for further details.
Related
In Flutter if I create a Timer, will the supplied callback get executed if the application is in background?
I think documentation is not clear on this or I might have missed it (please supply a link if you find it anywhere).
I just tried doing this with a timer set up to 10 seconds and it works fine.
I assume that is approach is not very reliable and other methods* should be used instead. I think if the app is paused/terminated by operating system to preserve battery or due to low memory, nothing will be executed. But for me this situation could be an ok approach.
* I know there are isolates so I guess I could spawn the timer inside one of these. Downside is that the isolate must be regular function (or static method) so no access to application data in my scenario. Then there are different scheduling packages etc but I'm trying to avoid these for now. I know about background tasks but I'm really looking for an answer on code execution using timers.
I am trying to figure out how to use a background thread to execute a command ever 4hrs.
I have never created anything like this before so have only been reading about it so far.. One of the things I have read are this
"Threads tie up physical memory and critical system resources"
So in that case would it be a bad idead to have this thread that checkes the time then executes my method... or is there a better option, I have read about GCD (Grand Central Dispatch) but I am not sure if this is applicable as I think its more for concurrent requests? not something that repeats over and over again checking the time..
Or finally is there something I have completely missed where you can execute a request every 4hrs?
Any help would be greatly appreciated.
There is a max time background processes are allowed to run (10 min) which would make your approach difficult. Your next best attempt is to calculate the next event as save the times tamp somewhere. Then if the app is executed at or after that event it can carry out whatever action you want.
This might help:
http://www.audacious-software.com/2011/01/ios-background-processing-limits/
I think that it would be good to make use of a time stamp and post a notification for when the time reaches for hours from now.
Multithreading is not a good means to do this because essentially you would be running a loop for four hours eating clock cycles. Thanks to the magic of operating systems this would not eat up an entire core or anything silly like that however it would be continuously computed if it was allowed to run. This would be a vast waste of resources so it is not allowed. GCD was not really meant for this kind of thing. It was meant to allow for concurrency to smooth out UI interaction as well as complete tasks more efficiently, a 4hr loop would be inefficent. Think of concurrency as a tool for something like being able to interact with a table while its content is being loaded or changed. GCD blocks make this very easy when used correctly. GCD and other multithreading abilities give tools to do calculations in the background as well as interact with databases and deal with requests without ever affecting the users experience. Many people whom are much smarter then me have written exstensively on what multithreading/multitasking is and what it is good for. In a way posting a message for a time would be method of multitasking without the nastiness of constantly executing blocks through GCD to wait for the 4 hr time period, however it is possible to do this. You could execute a block that monitored for time less then the max length of a threads lifetime then when the threads execution is over dispatch it again until the desired time is achieved. This is a bad way of doing this. Post a notification to the notification center, its easy and will accomplish your goal without having to deal with the complexity of multithreading yourself.
You can post a notification request observing for a time change and it will return its note, however this requires you application be active or in the background. I can not guarantee the OS wont kill your application however if it is nice and quiet with a small memory footprint in "background" state its notification center request will remain active and function as intended.
I'm developing a navigation app which uses the UIBackgroundModes=location setting and receives CLLocationManager updates via didUpdateToLocation. That works fine.
The problem is that the intervals between location updates are very hard to predict and I need to make sure the app is called something like once every few seconds to do some other (tiny) amounts of work even if the location did not change significantly.
Can I do that? Am I allowed to do that? And how can I do that?
I found a blog post, but I'm not sure if this is really the way to proceed.
Permissible background operations are pretty limited in scope. You cannot, for example, just leave an NSTimer running to perform some arbitrary code while your application is in the background - so the simple answer to your question is no, you cannot. Definitely read the Apple documentation regarding what is and isn't allowed (most of what's allowed pertains to apps that "need" specific ongoing services, like the ability to play music, or respond to location changes (GPS type apps...). You may be able to construct a viable solution by responding to location or significant location change notifications...
I would like for my iOS app when it is in background mode to execute at specific intervals some functions
(What I precisely want to do is to check a URL, and indicate its (int) content as a badge.)
However, I don't know how to have the function executed in the background.
Thanks.
Read about Executing Code in the Background. There is a limited set of things you can do in the background, what you describe not among them unfortunately.
I think you have two options to solve this problem each of them has pros and cons.
First, one is background refresh check the link. Have in mind that it is different for ios 13 and above. You need to define background tasks check here. It takes me some time to understand the background tasks but it seems more logical and easy to manage if you have several tasks. Still, you don't have the full control of when this task will be executed. It depends on how much battery, network and so on your task will use every time. The system will choose what is the best time to run it.
There is one more option, to implement a silent push notification check here.
Here you can implement a good push mechanism for updates but you will depend on network and permission for notifications. Also, you will need a backend for this solution.
You need to define what works best for you.
I think the best option is to use the voip background mode. Here you can find all the required information: how to run background process on the iOS using private APIs to sync email items without jailbreaking the phone
https://developer.apple.com/documentation/usernotifications/setting_up_a_remote_notification_server/pushing_background_updates_to_your_app
To update the content frequently when the app is in the background might be difficult, Instead, you can wake the app by pushing a silent notification from backend at regular intervals.
For more information check this article also
https://medium.com/#m.imadali10/ios-silent-push-notifications-84009d57794c
I am new to objective-c/cocoa programming. I am making an application which is to constantly sync with a server and keep its view updated.
Now in a nutshell, heres what I thought of: Initiate an NSTimer to trigger every second or two, contact the server, if there is a change, update the view. Is this a good way of doing it?
I have read elsewhere that you can have a thread running in the background which monitors the changes and updates the view. I never worked with threads before and I know they can be quite troublesome and you need a good amount of experience with memory management to get most out of them.
I have one month to get this application done. What do you guys recommend? Just use an NSTimer and do it the way I though of...or learn multithreading and get it done that way (but keep in mind my time frame).
Thanks!
I think using separate thread in this case would be too much. You need to use threads when there is some task that runs for considerable amount of time and can freeze your app for some time.
In your case do this:
Create timer and call some method (say update) every N seconds.
in update send asynchronous request to server and check for any changes.
download data using NSURLConnection delegate and parse. Note: if there is probability that you can receive a huge amount of data from server and its processing can take much time (for example parsing of 2Mb of XML data) then you do need to perform that is a separate thread.
update all listeners (appropriate view controllers for example) with processed data.
continue polling using timer.
Think about requirements. The most relevant questions, IMO, are :
does your application have to get new data while running in background?
does your application need to be responsive, that is, not sluggish when it's fetching new data?
I guess the answer to the first question is probably no. If you are updating a view depending on the data, it's only required to fetch the data when the view is visible. You cannot guarantee always fetching data in background anyway, because iOS can always just kill your application. Anyway, in your application's perspective, multithreading is not relevant to this question. Because either you are updating only in foreground or also in background, your application need no more than one thread.
Multithreading is relevant rather to the second question. If your application has to remain responsive while fetching data, then you will have to run your fetching code on a detached thread. What's more important here is, the update on the user interface (like views) must happen on the main thread again.
Learning multithreading in general is something indeed, but iOS SDK provides a lot of help. Learning how to use operation queue (I guess that's the easiest to learn, but not necessarily the easiest to use) wouldn't take many days. In a month period, you can definitely finish the job.
Again, however, think clearly why you would need multithreading.