I'm working on an swift application that uses a TableView. It's cells are filled-up with data that comes from a remote server. That's how my app works now, but I want to change this mode because I'm sure that it's not the correct way to do things:
First: when the tableview did load, I call a function that get data (json) from server with this method:
NSURLConnection.sendAsynchronousRequest(request, queue: NSOperationQueue.mainQueue())
After that, I save my data as an object in NSUserDefaults. The object contains strings such as username, description, location, picture... etc. I know that this is not correct to store images in NSUserDefaults even if these images are not so big...
Second: I fill up table's cells with data obtained from NSUserDefauts, where I have stored my json data.
First of all I want to know how to auto append data to the table when the user hits the last cell of the table, like all apps that uses tableviews for fetching user posts...
In Instagram, after the you close the app, disconnect from the internet, and reenter the app, it will show you the first 10 cells from the last table you've seen before closing the app, so Instagram saves somehow, somewhere, maybe in coredata, data for the first 10 cells.
How do you suggest me to do this?
Question is not particular.....
Load Data error.
Or you fetch the result from coreData error?
CoreData can save View and some informations.
Post your code.
Related
I need some help getting random data from core data using Swift 3, Xcode 8.3.1. I currently have an app that creates a list in tableview using data that is entered by the user.. (user enters a name and takes a picture of that person) The entity "Friend" holds the attributes "name", "image".
The first version of this app was just a name and I would use arc4random to randomly update a label with a name on a modally presented VC on a button click. The names were simply stored in an Array.
This version is including an image so I decided to try my hand at core-data (never used it before) and now I'm stuck at my random select button. Currently the app will store the data fine and then retrieve it and display everyone alphabetically along with their image in a tableview. As a new person is submitted the info gets stored and the tableview updates.
I need to show a randomly selected name and its image, but I don't know how to do this and research has failed me on getting it done.
If there is a better way of storing an image & name instead of core-data I'm open to changing as well. The app stores anywhere from 20-80 different names. It will never be used to store much more than that.
You can fetch your items from the context, which will give you an array of objects. Now you just use your favorite random function to get a random index for this array. And then use an object at that index.
Here is my context:
When I launch my app I fetch local data from CoreData and fill a tableview with it. At the same time I send an asynchronous request to my webservice to fetch what will be the new content of my tableview.
As soon as the request sends me a response I delete all the instances of the current NSManagedObjects and create new ones with the new data I got. Then I replace the datasource of my tableview to an array of the new NSManagedObjectContexts instances.
My problem:
I'm getting an error : CoreData could not fulfill a fault for ... if I scroll my tableview when the request finished and is triggering the deletion/creation of my tableview's data source.
I understand that this problem occurs because I'm trying to access an old NSManagedObject instance while doesn't exist anymore as it is explained in the doc : Apple doc. But I have no idea of what are the best practices in my case.
I don't want to block the user until my request finished but I have to prevent any error if he accesses "old" data while the request didn't finish (e.g : what if the user taps on a cell and I pass an instance of an NSManagedObject to another viewcontroller but when the request finishes this object doesn't exist anymore ?)
I would appreciate any help !
I highly recommend you to use NSFetchedResultsController since it's sole purpuse is:
You use a fetched results controller to efficiently manage the results returned from a Core Data fetch request to provide data for a UITableView object.
When using a fetched results controller it is much easier to handle the Core Data events like insert, delete, update.
You say you have three sections in your table view? That's no problem, NSFetchedResultsController can handle all of that.
Take a look at this. Apple provides a very nice set of instructions on how to configure and use NSFetchedResultsController.
I'm using Parse as the backend for my app. My app will be used in the field where service will nonexistent or spotty at best so I need to store information offline. I currently save data for the user in a plist in the background (Title, location coordinates, notes, additional data). Since Parse's current iOS offline saving is fairly poor (From what I've read), I was hoping to get around it by creating an array or dictionary from the plist and upload that to Parse by giving it an array once the user is back in cell range.
As it occurs now, when I upload the array, it simply puts the entire contents of the array in a single cell in the database. Is there a way to parse the array and create a new row for each entry/object in the array?
I may have overlooked a better way to do this. If someone has a suggestion I would appreciate it!
I solved it. I iterated through the array using a for loop and added each index as a separate object.
First I'll give a bit of background on what I'm working on. I'm creating a CRUD iOS application that gets information from an API we've created. Once I have pulled down the data I store it with CoreData. I then use an NSFetchedResultsController to display this data in a table view. Problem is that when I show a modal view on top of the table view and then dismiss the modal view, the table is cleared and everything short of re-downloading the data and inserting it again doesn't work.
The problem arises though when I'm pulling fresh data from the API. Using trial and error I have narrowed down the problem to where I delete all the old data in the persistent store (I have two stores, one for user created data and one for data from other users). This code snippet is from the API call where I handle fetching data:
[self deleteAllEntitiesNamed:#"Object"];
[self parseResponseObjectIntoManagedObjects:[response results] inStoreWithURL:storeURL];
success(response);
The [self deleteAllEntitiesNamed:#"Object"]; call goes into the store for other users and deletes all Object entities with the following code:
NSArray *result = [self performFetchRequestForEntityNamed:entity inStoreWithURL:url];
for(id r in result)
{
[self.managedObjectContext deleteObject:r];
}
I have traced the problem down to this function call. If I comment out the delete call in the API handler, there is no problem maintaining the table between views, though it has the bad side effect of duplicating a lot of the data already in the store. I feel I may be missing something about deleting items in the store, though it makes no sense to me as I re-insert the data immediately after deleting the old store.
I have tried deleting and re-initializing the entire store, but then no data loads at all.
Thanks ahead of time for any insight available.
EDIT: I should also add that when I have tried to pull out objects from the store after moving back to the table view, I get an empty result using the same fetch request that succeeds at getting Objects out of the store immediately after I finish the API call in my success callback.
I watched a video tutorial on CoreData. I saw a that an option
Uses Lazy fetching
To map an Object Model with Array Controller.
But did not understand what is Lazy fetching?
That means that data would be actually fetched (automatically) not a the time of request, but at the time when controller would ask for data. For example consider large tableview with thousands of lines - they are not fetched all at the same time when request is executed, rather they are fetched by small parts dynamically when users scrolls tableview.