I am new in iOS developer. Now I am working at a background location app. I need to send data to server and save some info from feedback. First time I save the data in UIKit class, but it seems released. Second time I save the data in static variables. It still crash. Then I have to use NSUserDefaults , it works . But is this OK? Any better way? Save data to local or something else ? Thanks~
The better way is to use NSUserDefaults, you save your data there and you dont worry about the data been released or removed.
Another way is global data or singletons, but is not recommended by Apple (you can find a lot of discussions about this in the internet)
I personally recommend you to use NSUserDefaults, if you have any doubt using it we can help you.
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I am using NSCache to deal with cache in my app. Can anybody explain to me how totalCostLimit and countLimit works.
I want to allow user input how may memory of using cache he wont to allow for our app and I understand that I need to use totalCostLimit and countLimit, but what happen to inputed data if user will close the app, will it be stored or cached somewhere by the app or I need to sore it in database and every time when user will open the app take that data and send it to totalCostLimit and countLimit.
Also I do not understand how to observe how much cache is weighting, I want to add that info to app so user whenever he wont will see hove much memory my app takes for cache in that specific moment.
Thank you for the answers!
I need to save my objects in permanent memory. The option I use right now is that i save my objects in the NSUserDefaults before my app quits and I retrieve them when my app starts running. This approach is not very convenient since I may lose important data in case the application crashes. Is there any way to store my objects, but when a property of an object changes, then this change is saved in the disk automatically? Except for that, there is a danger to mess the objects in ram and the objects in the disk using that architecture.
For example
-> Load objects from memory
-> [object1 setValue:#"5"]
-> Application crashes
After the crash, when the user opens the application, the value #"5" will not be available because I never saved the data.
Is there any alternative so as to make by code more safe and maintainable? CoreData is a good option for this problem , or is it an overhead?
If you need to save data, CoreData is the best. You can save after every change if you need to.
If saving info is so important you might want to figure out what could cause/is causing your application to crash and fix that. No matter how good a solution is if your app is going to randomly crash you'll probably lose some data.
It is really not the best of option to save data instantly when a value changes. It's way too expensive for app performance. You must continue using NSUserDefaults to store the values when app is force closed or entered in background.
Your app is designed by you. It MUST not crash but even if it does, don't worry. Anamolies cannot really be handled.
I have noticed that for a mobile application, saving on the main thread seems to take a bit when it compares to other applications on the device. Is it recommended to only save Core Data when the application enters the background or when an application closes instead of anytime items are added and sent / received from the api?
That's kind of a broad question, but I've found that saving core data after VewDidAppear statements is better than viewWill statements. Giving the user something to engage with and persisting makes it less noticeable than on a load. However, if a user is used to waiting for something like an activity loop, adding the save to that doesn't tax it too much (IMHO).
Not sure this help, just my experience.
Can you please give some suggestions on sqlite using on the iPhone?
Within my application, I use a sqlite DB to store all local data. Two methods can be used to retrieve those data during running time.
1, Load all the data into memory at initialization stage. (More memory used, less DB open/close operation needed)
2, Read corresponding records when necessary, free the occupied memory after using. (Good habit for memory using, but much DB open/close operations needs).
I prefer to use method 2, but not sure whether too many DB opening/closing operations could affect app's efficiency. Or do you think I can 'upgrade' method 2 by opening DB when app launches and closing DB when app quits?
Thanks for your suggestions very much!
First of all: use FMDB to access SQLite!
Then, create your own singleton "MyDB" class.
Every time you need the database, you do [MyDB instance] to get your FMDB instance.
That way you only have one DB open (in didFinishLaunching) an you close it when your app exits.
That's far and away the best way to use SQLite on the iPhone.
The other option is to use CoreData, something I find great for when you start with an empty database, but FMDB/SQLite works best for me if I have a set of data that's read-only.
Apple seems to suggest that you avoid preloading all the data during the startup in order to ensure faster and smoother startup. Supposedly you should only load data when/if the user needs it.
I was wondering what your thoughts were on persisting objects (NSDictionarys and NSMutableArrays of Objects) on the iPhone?
I've gone through a couple of options in my head:
1.) We persist using NSUserDefaults, this method seems the easiest and I sort of want to just go ahead and use this. The Data I want to store would only maybe be a few kilobytes of objects.
2.) Using NSKeyedArchiver (the exact name alludes me atm) to archive/serialize and then just puting that into a SQLITe database. but the problem with that is:
I need the data, when it's changed on the phone, to automatically be saved. NSUserDefaults has a synchronization method for this, but for method #2 I'd have to re-archive the entire array of objects, and then store it back into the database. This seems like a lot of work.
3.) forgot about this I've heard things about CoreData being able to handle this sort of thing, but I'm not sure if I understand exactly.
So what do you guys think? Do you have any other suggestions?
I recommend going the extra mile and use Core Data.
First you will learn a new thing, a good thing.
But further more your app will start up faster and handle data much more fluently as data is fetched in chunks rather requiring reading the whole dataset.
...don't be afraid, just try it. Start small and keep going.
I think NSDictionary and NSArray has writeToFile:atomically: instance methods that serializes and writes them to your given filename. You could add the observer for your NSDictionary or NSArray which writes them after they get changed.
I've used both NSKeyedArchiver and writeToFile:atomically: on a few of my own apps with great success.
Performance has been great. You can repeatedly persist a few thousand lines of text and not notice.
Personally, I avoid sqlite unless you need querying. You'd be surprised what you can get away with using only NSDictionary filled with NSArray
The advantage to using NSKeyedArchiver is once you start creating "Domain Objects", you can persist those the same way. For this reason, I use NSKeyedArchiver 99% of the time.