IOS Core Data, UITableView load more data - ios

Question

in my IOS project i using Core Data. I have 1000 elements
First of all, I need to show in UITableView 30 elements. When the user scrolls and reaches the bottom of an UITableView (5 elements to the end) so I can load new data into the table.
How can i do that
I used this code but it does not work the way I wanted
#import "HomeViewController.h"
#import "GDMnLineRKObjectManager.h"
#import "CoreData+MagicalRecord.h"
#import "CinNames.h"
#import "Event.h"
#interface HomeViewController ()<UITableViewDataSource, UITableViewDelegate, NSFetchedResultsControllerDelegate>
#property (weak, nonatomic) IBOutlet UITableView *tableView;
#property NSUInteger dpc;
#property BOOL is_load;
#property BOOL process_loading;
#property NSFetchRequest *fetchRequest;
#property (nonatomic) BOOL loadingMoreTableViewData;
#property (nonatomic) NSUInteger inf_counter;
#end
#implementation HomeViewController
//#synthesize tableView;
- (IBAction)showMenu
{
// Dismiss keyboard (optional)
//
[self.view endEditing:YES];
[self.frostedViewController.view endEditing:YES];
// Present the view controller
//
[self.frostedViewController presentMenuViewController];
[self.tableView reloadData];
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
}
- (void)saveToStore
{
// Saving to persistent store for further usage.
}
- (void)viewDidLoad {
[super viewDidLoad];
self.dpc = 0;
self.inf_counter = self.dpc;
self.is_load = NO;
self.process_loading = NO;
self.fetchRequest = [NSFetchRequest fetchRequestWithEntityName:NSStringFromClass([Event class])];
// Do any additional setup after loading the view, typically from a nib.
/*
*/
[self loadElements];
////
[self.tableView setDelegate:self];
[self.tableView setDataSource:self];
///
}
- (void)loadElements
{
// Get an array of remote "character" objects. Specify the offset.
[[GDMnLineRKObjectManager manager] getMnLineObjectsAtPath:SERVER_PATH_LOAD
parameters:#{#"someval" : #("564")}
success:^(RKObjectRequestOperation *operation, RKMappingResult *mappingResult) {
}
failure:^(RKObjectRequestOperation *operation, NSError *error) {
// Failed to load characters.
/*
[self animateActivityIndicator:NO];
[bottomPullView finishedLoading];
*/
[[[UIAlertView alloc] initWithTitle:#"Marvel API Error" message:operation.error.localizedDescription delegate:self cancelButtonTitle:#"Cancel" otherButtonTitles:#"Retry", nil] show];
}];
}
#pragma mark - Table View
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView {
return [[self.fetchedResultsController sections] count];
}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
id <NSFetchedResultsSectionInfo> sectionInfo = [self.fetchedResultsController sections][section];
return [sectionInfo numberOfObjects];
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
NSLog(#"III = %#", indexPath);
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:#"HuCell" forIndexPath:indexPath];
[self configureCell:cell atIndexPath:indexPath];
if (indexPath.row > self.inf_counter - 5) {
// User has scrolled to the bottom of the list of available data so simulate loading some more if we aren't already
if (!self.loadingMoreTableViewData && self.process_loading == NO) {
self.loadingMoreTableViewData = YES;
self.process_loading = YES;
[self performSelector:#selector(addSomeMoreEntriesToTableView) withObject:nil afterDelay:0.0f];
}
}
if (indexPath.row < self.inf_counter) {
[self configureCell:cell atIndexPath:indexPath];
} else {
cell.textLabel.text = #"Loading more data...";
}
return cell;
}
- (void)configureCell:(UITableViewCell *)cell atIndexPath:(NSIndexPath *)indexPath {
NSManagedObject *object = [self.fetchedResultsController objectAtIndexPath:indexPath];
NSString * string3 = [NSString stringWithFormat:#"%# - %ld", [[object valueForKey:#"name"] description], (long)indexPath.row];
cell.textLabel.text = string3;//[[object valueForKey:#"name"] description];
}
#pragma mark - Fetched results controller
- (NSFetchedResultsController *)fetchedResultsController
{
NSLog(#"Skolko");
if ((!_fetchedResultsController || self.process_loading == YES)) {
self.process_loading = NO;
self.is_load = NO;
NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:#"timeStamp" ascending:NO];
self.fetchRequest.sortDescriptors = #[sortDescriptor];
self.fetchRequest.fetchLimit = self.dpc;
//self.fetchRequest.fetchBatchSize = 30;
self.fetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:self.fetchRequest managedObjectContext:[RKManagedObjectStore defaultStore].mainQueueManagedObjectContext sectionNameKeyPath:nil cacheName:nil];
self.fetchedResultsController.delegate = self;
NSError *error;
[self.fetchedResultsController performFetch:&error];
NSLog(#"%#",[self.fetchedResultsController fetchedObjects]);
NSLog(#"Counta: %lu",(unsigned long)[self.fetchedResultsController.fetchedObjects count]);
NSAssert(!error, #"Error performing fetch request: %#", error);
self.inf_counter = [self.fetchedResultsController.fetchedObjects count];
[self.tableView reloadData];
}
return _fetchedResultsController;
}
- (void)addSomeMoreEntriesToTableView {
self.dpc += 20;
[self fetchedResultsController];
self.loadingMoreTableViewData = NO;
[self.tableView reloadData];
}
- (void)scrollViewDidScroll: (UIScrollView*)scroll {
// UITableView only moves in one direction, y axis
CGFloat currentOffset = scroll.contentOffset.y;
CGFloat maximumOffset = scroll.contentSize.height - scroll.frame.size.height;
NSLog(#"hui = %f", (maximumOffset - currentOffset));
// Change 10.0 to adjust the distance from bottom
if (maximumOffset - currentOffset <= 10.0) {
self.is_load = YES;
self.dpc += 10;
[self fetchedResultsController];
//[self.tableView reloadData];
}
}
#end

Answer 1

What you are looking for is the fetchBatchSize property on NSFetchRequest. I hope you are also using an NSFetchedResultsController, it goes fantastically well with Table Views and Collection Views. Here's the description:
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.
So before you setup your fetched results controller just ensure you set the fetchBatchSize of the fetch request and let the framework handle all the optimizations for you.
EDIT
The OP wanted the original fetch to only include 30 items and then only if the user scrolled it should repopulate the fetch. In most cases fetchBatchSize should be the solution as Core Data will seek to fault all the results and thus avoid the overhead of fetching all the objects, preferring to lazily fault them instead. To stick with the OP, the solution might be like this:
- (NSFetchRequest *)createFetchRequest {
NSFetchRequest *fetch = [NSFetchRequest fetchRequestWithEntityName:NSStringFromClass([MyEntity class])];
fetch.predicate = //set up your fetch
return fetch;
}
And then when you instantiate your controller you can set the fetch limit:
NSFetchRequest *fetchRequest = [self createFetchRequest];
fetchRequest.fetchLimit = 30;
NSFetchedResultsController *controller = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest
managedObjectContext:context
sectionNameKeyPath:nil cacheName:nil];
self.controller = controller;
since the fetchRequest property on the controller is readOnly you are forced to re-assign your controller when you want to fetch everything:
NSFetchRequest *fetchRequest = [self createFetchRequest];
NSFetchedResultsController *controller = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest
managedObjectContext:context
sectionNameKeyPath:nil cacheName:nil];
[controller performFetch:nil];
self.controller = controller;
If you want even more to go on, head on over to Ray Wenderlich, they provide awesome tutorials for everything iOS.
Happy Coding

Answer 2

Options:
Watch the session Advanced ScrollView Techniques from WWDC 2011.
Tutorial: http://mobiledevelopertips.com/user-interface/creating-circular-and-infinite-uiscrollviews.html