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
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I am really confused on what the Core Data actually is. Or I guess my question is, when dealing with a database, would you use Core Data? Like if I wanted access values from a database would I be using Core Data to access those values? How would I approach this problem?
Thank you so much for the help.
Core Data is an framework that does the work of "object persistence". In other words, it's code you can use that takes care of saving a collection of objects to disk and loading them again later. It does a lot of work to allow you to store lots of data and load only the objects you need at a time, and unload ones when memory is tight.
Core Data can use a database to accomplish this, but that's it's business, not yours. When you use Core Data, it is a black box. You tell it to save the data and then step out of the way.
If you want to interact with an existing database, such as a MySQL database on a web server, that's a completely different matter. You might use Core Data to store local copies of objects on your device, but in that case Core Data won't care that the objects are copies from some other database. It doesn't care.
It is a convenient, native means of storing data in your iOS applications. Don't think of it as sqlite although you can view the files it creates with various sqlite tools. Instead think of it as a tool for manipulating an object graph of information important to your app.
I've used it in two main ways. First to store a bunch of static data that is important to an app, in one case that was a large amount of location data for an indoor mapping application. What arrived as a massive CSV file of waypoints was converted to core data. Core Data was incredibly useful for this because it allowed preparing a sqlite file which was shipped with the application containing all the infomation. Updates from a web service arrive as more CSV that is added to the Core Data to keep information current. At runtime the location information object (the waypoint a user is at) is retrieved with a predicate (i.e. the point they tapped on) and that object, through its Core Data relationships, indicates where it is possible to go from that point. Core Data provided the information necessary to perform A* routing through the indoor map.
Second it is great when you have a bunch of objects arriving as JSON and you want to be able to store and access those objects later. Let's say you have a typical app where you have a User and some information about the User, let's call it Thing. Users have Things. When you want to know something about a User you retrieve the Core Data record using a predicate - typically "name" or similar - and you get all the information you stored about the User back. Again you can make use of relationships to explore the user's connections and make displaying information easy. Perhaps the User has many Things, then you can say "user.things" and you get a NSSet of NSManagedObjects representing those Things.
You use it like a database. Its utility is that it is easy to access from anywhere in your iOS code, it is easy to store and easy to retrieve information also. Faulting lets you retrieve one object and navigate to any object connected through relationships by following the relationships. Because you define the attributes and relationships yourself in the data model editor it is easily customized for what you need to store. To me it is one of the most used and most useful parts of iOS.
When you want to automate display of information from Core Data you can use a NSFetchedResultsController to initiate a fetch and to respond through delegate methods to changes to the underlying data. If you set up a UITableView to use a NSFetchedResultsController as data source, you can have the table automatically update whenever the objects displayed in the cells changed. Very useful for apps where you periodically update information and want what is displayed to be kept current.
When your object model changes it is possible to maintain all of your existing information and migrate it to the new model. Core Data manages automatic (lightweight migration) when it can, or if you have made more radical changes you can supply rules to handle the migration.
The limitation of Core Data is that it is not great for storing binaries. If you have images that you need to store, far better to store a path to the location of the image than trying to store the actual data.
Yes, if you want a local database on your device, Core Data is the appropriate technology. It probably makes sense to start your research with the Core Data Programming Guide.
You can alternatively use SQLite (which Core Data uses in the backend), but Core Data offers some material advantages and is the preferred database interface for iOS. If you decide to pursue SQLite for any reason, though, I'd suggest you contemplate using the FMDB Objective-C SQLite wrapper.
But Core Data is generally the way to go.
Hi I am a newbie to iPhone programming. I have been looking at some tutorials online for using SQLite on the iPhone.
From what Iv'e seen, one has to read the entire database in the app delegate method and then store the contents in an array. This is then used to populate a UITableView.
I was wondering how this can be efficient? I mean, if you are going to store the contents of your entire database in memory why have a database?
Is this standard practice?
Instead of this, if I use Core Data, I can set the paging size and it will optimize how much data is stored in memory and only read whats being shown within the visible cells.
Is there anyway, In can have the same functionality using SQLite? so its easy on memory. I mean my database has only 300 entries now, but what if in the future it has 3 million?
Can some one please assist me in understanding this....
Are there any tutorials for SQLite that show how to do it in an optimized way?
Thanks
I would suggest using Core Data. It's extremely powerful, better supported than a SQLite table, and not as complicated as it looks, it just uses a lot of "managed object" jargon which can be daunting at first. Check out the CoreDataHelper class, and a few tutorials. I was able to get Core Data working in a few days (in my first ever app) using the links in my comment
If you're familiar with SQL, basically Core Data works like this: the Persistent Store IS a SQLite table, but you never access it directly; the managedObjectContext is where you do all the data work in your program (and don't forget to save it to the persistent store!), while an Entity is a table, attributes of that entity are your columns, and a managed object is a row.
Further Reading:
Core Data Tutorial - YouTube
Core Data Tutorial: Getting Started | Ray Wenderlich
iPhone Core Data: Your First Steps
Here is some tutorial that may help you:
iPhone Programming Tutorial.
I recommend you consider using core data instead of sqlite.
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'm trying to add Core Data to an app that loads news form of an RSS feed so I can store articles offline. I am using ASIHTTP to load the data off of the internet as XML.
I'd like to store the articles in Core Data so I have them the next time I start. My AppDelegate_shared already is set up for Core Data, based on the template, but I'm not sure where to add all the rest of the code.
I found a tutorial by Ray Wenderlich, but it only confuses me. His tutorial assumes that there is a single App Delegate file, not three, as created by the Universal App templates.
Where in my three AppDelegate files (the shared, iPhone and iPad specific) does my core data article entry code go?
Are there any tutorials that deal with Core Data with the newer app template setup (3 delegate files)?
How do I read out my Core Data into a UITableView?
The Core Data stack only needs to be created in one shared location at startup. You can still have three different application delegates, as long as all three call the same setup routine. This could be done by making all three application delegates you have be subclasses of one base application delegate which handles this setup.
Another way to approach this might be to create a singleton for managing your Core Data access. See this question for other potential configurations that people have used, as well as the reasons for them.
As far as how to populate a table view with data from a Core Data database, you'll want to use NSFetchedResultsController for that. It makes displaying and updating table views simple on iOS. Jeff LaMarche has some good template code for dealing with this, and the sample applications generated when creating a new navigation-based Core Data iPhone application show this in action.
Finally, I taught a class on Core Data last semester (and finished another one last night), for which the course notes are available here and the video can be downloaded from iTunes U.
the core-data stuff belongs to the shared appdelegate. because the other two appdelegates are just subclasses of the shared one.
why not create a new universal project with coredata and look how it's done? and to see how the data is feed into a tableview, you could create a navigation-based project with coredata and look how it's done in there.
I would like to begin work on an iPhone app that does little more than display a books content for reading. The book content is available online, and is fully open source, but I would like to make the content available locally. With apps that I have worked on previously, namely with iPhone OS 2.X, creating (or finding) an .sql database and then just making queries for data from within the app worked really well. With the advent of Core Data (which I am not that familiar with) the older sql method may not be ideal. So my question is: What is the best way for me to go from online web content to locally stored iPhone readable content? Regardless of which approach I take, I am going to need a db (right?), so should I get the brunt of it out of the way and start with importing the web content into a db with all of the correct tables and columns? I guess with this question, I am just looking for a point in the right direction. If there were any suggestions about the best method for me to get rolling on this, it would be greatly appreciated. Thanks!
Core Data is good if you have "objects" that you want to make persistent. In the case of having just a lot of data to read/write, plain old SQLite may be simpler.
Sorry that I can't give any more specific advice, but it comes down to how complicated your app's data model and object models are. I'd recommend looking at Core Data, but don't use it just because everybody tells you how cool it is.
If you go with Core Data, you won't define your own SQL database schema, so don't start down that path until you've made the decision.
I actually would go with the Core Data route. Core Data is just an API provided by Apple to manage persistent data no matter the data backend (wether it is a flat plist file, an XML file, or a full sqlite database file).
In the case of a book, you can break down the entities as follows.
Book Entity
Title which is a String Attribute
Author which is a String Attribute
chapters which is a has many relationship of Chapter Entities
Chapter Entity
Title which is a String Attribute
pages which is a has many relationship of Page Entities
Page Entity
PageText which is a String Attribute
Then you can access all the values as if they are objects using Core Data without having to worry about the SQL backend code, and writing all the code to translate the SQLite datatypes to Cocoa objects that your view controllers can display.