I needed some advice on how to get the data from the database(sqlite). I am having a navigation based application. The db i have, contains a CONTACTS table.For each row in CONTACT, another table CONTACT_DETAILS contains around 50 rows.
The data from CONTACTS i have to load at application startup as i have to show them on the first page of application. Now about the CONTACT_DETAILS, here i am a little confused about how to load the data from the database.
Shall i load all at once on application load? Or
Shall i load this data only on selection of a particular contact?
Short answer: use CoreData and you wouldn't have to worry about it.
Slightly longer answer: it depends (ok, that was shorter). If your database is small and you aren't going to update it, you might just as well load it at launch; but if you are updating or it is larger, load the details when you call the view controller from the master - typically in the viewDidLoad (or viewWillAppear, again, depending).
Related
I'm making an app where the user can take a picture and add a title and description. But now I need to store the picture and the titles. I’ve tried making an object that contains title, description and image properties.
When it’s done I save an array of custom objects with the information on it with UserDefaults. My idea is showing in another view a table view with all the content and pictures the user has taken on the cells. I tried getting back the information with user defaults. It was working well until the user saves too many pictures. When the viewController with the tableview loads, then my app gets slower, and eventually it crashes.
I suppose the problem is when I load all the array with all custom objects, all the pictures are loaded into memory although they aren’t used and displayed for users. So I think it isn’t the best way to make what I want to make.
Is there any way better to make what I’m making or store data more efficiently and use it in tableview without using all the memory of the device?
I’m making the app from 0 again.
Can you show me how to store data and images efficiently?
There are several options for permanently storing user data on the device such that it will survive app and phone restarts. NSUserDefaults typically is for small amounts of data, such as user preferences.
When it comes time to store a lot of data, in particular big binary objects like photos, you need to decide which design you want to use. One option:
store all the photos in one directory in your apps documents and then use some simple lookup store (perhaps Core Data, or SQLite, or even a flat file) to index the photos and their metadata. Or if you don't care about indexing you can read the list of file names from the directory and sort them by time.
The other problem you are maybe having is that you are trying to load all of the photos at once for the user. As you have discovered, once you have more than a handful of photos this system falls apart. You need some mechanism to load only a few photos at a time, preferably only the ones the user needs to be displayed at that moment.
So, for example, if you are displaying the photos in a tableview, you want to only load the 10-15 photos that are visible in the table at any given time.
When storing this kind of data, you have 2 options (In fact you have more than 3 options, but saving image to the disk is IMHO complicated for this.) -
UserDefaults
Database like CoreData/Realm/FireBase...
The first one is recommended when there is not much data to save... For operating with more data, I would use database - CoreData...
For you operation you can use CoreData and NSFetchedResultsController (which is designed especially for fetching objects from the database)...
you can read the FetchedResultsController doc here... and core data basics here
Wish you best luck!
I have a tableview where i need to show around 10,000 rows (data stored locally in sqlite)
But when we jump to that view, app is getting blocked (freezed) as its loading all those rows.
Is there anyway to load data without freezing UI?
PS. Our app is rejected, is it because of this reason?
Thanks
EDIT:
They rejected and given following info
"Hello.
We noticed your app lacks native iOS functionality.
Please check out the videos for app design information,: "Getting Started
video: The Ingredients of Great iPhone Apps" and "iPhone User Interface
Design," available on the iOS Developer
Centerhttp://developer.apple.com/devcenter/ios,
and the iOS Human Interface
Guidelineshttp://developer.apple.com/library/ios/documentation/UserExperience/Conceptual/MobileHIG/MobileHIG.pdfin
particular, the sections, "Great
iOS Apps Embrace the Platform and HI Design
Principles"http://developer.apple.com/library/ios/#documentation/UserExperience/Conceptual/MobileHIG/Introduction/Introduction.htmland
"Human
Interface Principles"http://developer.apple.com/library/ios/#documentation/UserExperience/Conceptual/MobileHIG/Principles/Principles.html%23//apple_ref/doc/uid/TP40006556-CH5-SW1."
With ten thousand rows you have no choice but load your data on demand. Otherwise, your app has no chance of performing at a decent level. A freeze like you describe would definitely be enough to see your app rejected1.
This approach is rather wasteful with memory, too, because out of ten thousand rows you need at most two dozen at any given time.
A reasonably simple way to speed things up is to prepare an NSCache for your pages of data (say, ten items per page), add code that gets the total count of records, and modify the code that retrieves the data to read records from a single page (use LIMIT/OFFSET). When your table shows rows, it should try getting a page of the row from the cache. If the page is not there, it should load it from sqlite, and put in the cache. Using pages will minimize the number of roundtrips to the database; using cache will let you manage an optimal use of memory.
1 It does not look like your app has been rejected for a freeze this time around, but once you fix the "lacking native iOS functionality", the freeze will trigger another rejection.
Check this demo for lazy loading of all data along with images.
This sample demonstrates a multi-stage approach to loading and displaying a UITableView. It begins by loading the relevant text from an RSS feed so the table can load as quickly as possible, and then downloads the images for each row asynchronously so the UI is more responsive.
I come to iPhone programming from a web development paradigm and am having a bit of a problem understanding how to design my iPhone application.
The crux of my question is: How much data do you load into your model and when do you load it with data from the database?
In the web apps I've created, the objects on the server-side are filled by the database based off form values supplied by each request. Take the example of a simple list. You click a list value, the id for the list is sent to the server (query string), the server loads an object for just that list item, server-side code uses the object, and then destroys it before the page is returned to the user.
With iPhone apps (or I guess any app where objects persist), you could load all the list item objects into a singleton dictionary from the database before the user ever interacts with them. Then you never have to go back to the database when the user clicks on a link. You just load the object from the dictionary.
Alternatively, you could design it like a web app and just go back to the database each time and fill the object with the data requested.
Can you give me any guidance on when to use one way over the other? When do I load the data? I'm tempted to just load a bunch of data when the application starts up so that I never have to go back to the database. But this feels dirty.
For static data that isn't too large, loading it all at startup works.
In one of our products, we do this for simplicity on one of the tables (we don't expect more than a few thousand rows) and load the other table lazily (high-res images). This is a reasonable option if you don't have background threads also accessing the database.
Core Data does batched lazy loading (i.e. it will load a batch of result rows at once).
Sidenote: Writes using Core Data and an SQLite store seem exceptionally slow, to the extent that we moved processing to a background thread to avoid blocking the UI (and this is for not very much data at all) and gained some annoying concurrency issues as a result. Sigh.
My app has various pins that drop onto a map and when you click on the pins you get more information about this entity.
Each time you click on the entity it retrieves the information from a web service. Should I only retrieve this information once and store it in memory or should I retrieve it each time that page loads?
It's a small about of text and 3 small images?
If its just 3 small images and some text that will not change i would probably cache them in the application instead of retriving them over and over, it will provide a better user expirience in my opinion...
Also I have a Core Data application that uses images...
I tried both methods but I chose to retrieve it every time because for my goal is the best practice. However this method causes me to write some code and a lot of if and else!
How Daniel said, cache each image can be a better solution for your problem because if an user would like to retrieve these images from internet but the connections isn't fast, he'll wait a lot of time...
I'm building an app that retrieves a JSON dataset from a PHP server. The app has a view that displays a "feed" of several different newly added or updated items from the web server.
The app loads 20 of the newest items to start with, and the user can subsequently load 20 more older items, and 20 more, and so on. I want this data to persist between subsequent view changes, and quitting/launching the app.
So far I have a PHP webservice handling the JSON response by accepting a last_updated timestamp, which is sent by the iphone client with the webservice query. The server then returns any items it finds that are newer than the last_updated time.
On the iPhone side I have the connection to the webservice returning results to the iphone and displaying them in custom UITableViewCell cells. However as of right now the app will request the data from the webservice every single time.
I'm a little confused as to what's a good way to cache this data. Do I store the actual cells themselves, or create an object for each feed item type and store that? Or something else? Do I use core storage, sqlite, or some other custom method?
Thanks for any insight.
You never store data of any kind in a table view cell. Cells are intended to be reused to create the illusion of an arbitrarily long table. If you keep creating and retaining the cells as a data store you will eat all your memory very quickly.
It sounds like you do want to create a Core Data store although a plist and SQL are inferior options. The learning curve for Core Data is relatively steep but once you learn it it makes everything easier.