I create an application that retrieve data from websites(that's not mine) and save to core data. I want to create the notification when the new record have been inserted to my core data. I think the retrieve data method and add objects method should be run on the background but how can i do that? any sample code?
You really should build a basic understanding of multithreaded programming before you jump into this, and that's rather a bigger subject than we can reasonably cover in an answer. Start by reading Apple's documentation on the topic:
Threading Programming Guide
Concurrency Programming Guide
This isn't easy to do. Using Core Data in a background thread requires you to have a separate context for that thread. I'd suggest starting out by reading the Core Data Concurrency Guide. Also read the guides that Caleb linked to.
Once you figure out how to get your background context running, you'll most likely want to subscribe to the NSManagedObjectContextDidSaveNotification to update the UI on the main thread.
[self performSelectorInBackground:#selector(yourMethod:) withObject:];
You have to perform an async request [wich won't be performed on the main thread], and you will be notified about request completion/error/timeout in a delegate method, based on the library you are using.
I have experience with RestKit, you will find plenty of examples in the repository.
You mention creating a notification when inserting data into CoreData. Couldn't you just watch for the notifications sent by CoreData, like NSManagedObjectContextDidSaveNotification?
Related
I'm about to implement caching on my app, I imagine there are already good patterns on how to do that.
I think I'm going to use Core Data but I was wondering the best way to do that.
Most of the doc I found are just for Core Data tutorial.
What I do is to generate the NSManagedObject but then I also use a similar class with my additional methods, this to be decoupled from future fields addition keeping the generated one independent.
Is there some tutorial on the best way to handle object caching with Core Data?
Thanks in advance.
For keeping the hand-written code separate from the machine-generated code when using Core Data, have a look at mogenerator. Very useful.
As far as caching goes, Core Data's pretty decent, and with judicious use of batch faulting and pre-fetching, you can fairly easily manage the number of trips to the persistent store. The faulting mechanism works well in my experience, so be wary of premature optimisation when it comes to Core Data.
The advice Apple gives here is good, in particular use the profiling tools to see the part of your app that isn't working efficiently, and then address that specifically, rather than spending time writing code for a problem that doesn't exist.
Caching to file system is discouraged on iOS. Use Core Data for permanent storage, not temporary caching when possible.
There are however two in memory caching facilities provided by Apple.
NSURLCache for caching responses using the URL loading system (NSURLConnection and friends.). Simply create a new instance, and set it using +[NSURLCache setSharedURLCache:].
NSCache for caching any object. Just create an instance, add and fetch cached object using keys like form a normal dictionary collection. Supports both count and cost limits, as well as locking cached objects using the NSDiscardableContent protocol.
You could also use a in-memory NSPersistentStore for Core Data if you like to work with managed objects, that are only to live for one execution of the app.
I have started development of an app which is data reliant. It has a lot of information (using probably only 2 tables) so I am thinking core data is the way to go. However, I hate apps that only work when the user has an internet connection.
So what I would like to do is have saved core data on the device, and only download updates either periodically, on users' request or give them the option to update data when the app has loaded.
Is this the best solution and could someone please point me in the direction of a good blog or tutorial for this.
Many Thanks
The topics you ask about are really unrelated.
To implement your apps data model, Core Data is a fine solution. The iOS docs and sample code are good. if you need more I'm sure there are various blog posts but I don't have a recommendation. If you run into specific problems/issues there is tons of stuff on SO as well.
If you don't want to require a connection that's fine. This has nothing do with core data. It does have to do with apps functional requirements. At a minimum, store the apps current state in the data model and update at whatever interval you like, checking for a connection if that's required. Basically, whatever your app does, if a function requires a connection reflect that in the UI. Everything else should work fine without a connection.
I was thinking of writing some UIViewControllers to display the data in my Core Data stores while developing and testing an app.
I was thinking of something like this: A view controller that allows the user to select parameters to be passed into a fetch request, then a table view controller to list the fetch results, and finally a view controller to display the data in a particular entry from the fetch results.
Does anyone know of some open source code already similar to this, or a different approach I should take for monitoring my data?
NOTE: To clarify, I'm talking about a generic solution that could be put into any app using CoreData with minimal configuration.
Not a direct answer to your question but there is a new app in the mac app store which allows you to view and manipulate Core Data Stores. While it doesn't integrate in with your own app (and its not the cheapest software out there) you might find it helpful. I stumbled across it a few moments ago and thought of your question here.
http://itunes.apple.com/us/app/core-data-editor/id403025957?mt=12
So I have been doing lots of reading and found out NSCache is not persistent which is a slight problem for what I need to do. I have heard that I will need to use Core data instead... but I don't have any experience with core data so am wondering if its the only solution for persistent data.
The app will allow the user to search through a catalog, by typing in a search parameter in the code and select a distributor for their search parameter. What I want to do when the app loads is download the list of distributors and save them to a "cache" the will be persistent (till when the header I will make at some point changes and demands the app to update the cache), so that if the user turns the app of or the phone next time then open it the manufacture.
Now that I'm getting abit deeper into my app I'm getting abit lost in things for instance how would setting up a cache work with regards to NSURLConnection.
Any suggestions or code examples would be greatly appreciated..
This previous answer of mine might help you decide.
To sum it up:
If your data is small, static and low-complexity, use a collection class and write it to disk using the built-in class methods
If the data is static, low-complexity but large, SQL may be a good solution especially if you already know it.
If the data is dynamic and complex regardless of size, then Core Data is your best choice.
Viewed purely from the technical perspective, Core Data is always the best choice for iOS/MacOS API apps. Core Data is not just a persistence API, it is an API for creating the model layer of the Model-View-Controller design paradigm that the Apple API uses. It not only persist the data, but models it, validates its and provides an easy interface to the rest of the API.
If your going to be writing iOS apps, you need to eventually learn Core Data. However, it does have a learning curve and you should pick the method right now that will let you ship a usable app.
You can also check out sqlite. Here's another question that discusses getting started with sqlite on the phone: Where's the best SQLite 3 tutorial for iPhone-SDK?
The advantage to sqlite is that it is fairly easy to pick up. The downside is that you have to write queries for everything, and that can be a pain. It doesn't save objects, just data, numbers or text.
I am new to the iphone platform and am creating an app that retrievals a rss feed and displays it in a UITableView. I have gotten this working perfectly (or rather, the way I wanted). What I was thinking was I would store the current feed items on the phone so that it would initally load the old items it has stored while it got the new feed, then parse the new feed and add the new items and refresh the TableView. I was going to use Core Data to store it the old feed items because it would be a good way of learning Core Data and it would be an appropriate use of Core Data. However, I am having a difficult time learning how to use Core Data and connecting it with the Table/Array.
I have already googled and looked on stackoverflow for tutorials but have yet to find anything that explains it in a way I really understand. Any explanation of the overall steps that it takes to add Core Data to an existing app would be greatly appreciated. Full-blown detail are not necessary (but would also be useful). I'm just not very experienced with SQL or storing of data in such a manner and am having trouble wrapping my head around how the whole concept of Core Data works and how it connects to everything.
Also, any better method of doing what I'm trying to accomplish would also be appreciated.
There exist Xcode templates for Core Data-based applications; these are a great start to getting Core Data off the ground. However, it sounds like you want to integrate Core Data into your existing app, so you'll need to...
Add three main Core Data objects: the managed object context (MOC), the managed object model (MOM), and the persistent store coordinator (PSC). These need to be accessible wherever you want Core Data available, so either in your app delegate or, more preferably, in the controller or data source for your table view.
Create a MOM in Xcode. This will be a file of type .xcdatamodel, and it's an object graph that defines all the Core Data entities you want in your app.
Use NSFetchedResultsController (as suggested by Louis Gerbarg) to get data out of Core Data and display it into your table view.
Add code in your existing RSS-fetching-and-parsing routines to store new Core Data objects back into the store, when appropriate.
A good way to start is just to create a new Core Data application and play around with it a bit; you can also look at Apple's fantastic resources on the subject, like the Core Data Programming Guide and the sample apps Recipes and Locations. (Developer registration may be required.)
One last thing to note is that for the most part, a lot of the Core Data code you need to add can be ripped straight out of one of the Xcode template apps and pasted into your program (this holds especially true for the accessors for the three Core Data objects you need). Be careful not to use code you don't understand, though.
If you are using CoreData to populate a UITableView you really want to use NSFetchedResultsController as opposed to trying to populate and sync array yourself. The documentation for NSFetchedResultsController includes links to several CoreData tutorials, including onces that populate table views.
NSFetchedResultsController is still a bit buggy and requires fragile workarounds. I would start with the simpler iPhone Core Data "location" tutorial before moving on to the Books tutorial.
Also, any better method of doing what I'm trying to accomplish would also be appreciate
yes, it sounds like Core Data might be overkill for your application. Assuming your feed items are stored in a collection object you can easily use OSX's built in serializaition.
Been noted in other Stack-Overflow posts, but I can highly recommend the Prag Prog book "Core Data: Apple's API for Persisting Data on Mac OS X" - most is also relevant to iPhone Core Data apps; there is a whole chapter on creating an iPhone app too.
http://pragprog.com/titles/mzcd/core-data