FetchedResultsController header example

#import <UIKit/UIKit.h>


@interface NewsListViewController : UITableViewController <NSFetchedResultsControllerDelegate>{
	NSFetchedResultsController *resultsController;
	UIButton *sponsor;
}

@property (nonatomic, retain) NSFetchedResultsController *resultsController;


@end

helpers

NSInteger intSort(id num1, id num2, void *context)
{
    int v1 = [num1 intValue];
    int v2 = [num2 intValue];
    if (v1 < v2)
        return NSOrderedAscending;
    else if (v1 > v2)
        return NSOrderedDescending;
    else
        return NSOrderedSame;
}

- (int) getMaxUpdated: (NSString*)entityName key: (NSString*)keyName {
	int result = 0;
	[self managedObjectContext];
	NSFetchRequest *request = [[NSFetchRequest alloc] init];
	NSEntityDescription *entity = [NSEntityDescription entityForName:entityName inManagedObjectContext:managedObjectContext];
	[request setEntity:entity];
	
	// Specify that the request should return dictionaries.
	[request setResultType:NSDictionaryResultType];
	
	// Create an expression for the key path.
	NSExpression *keyPathExpression = [NSExpression expressionForKeyPath:keyName];
	
	// Create an expression to represent the max value at the key path 
	NSExpression *maxExpression = [NSExpression expressionForFunction:@"max:" arguments:[NSArray arrayWithObject:keyPathExpression]];
	
	// Create an expression description using the minExpression and returning a date.
	NSExpressionDescription *expressionDescription = [[NSExpressionDescription alloc] init];
	
	// The name is the key that will be used in the dictionary for the return value.
	[expressionDescription setName:[NSString stringWithFormat:@"max%@", keyName]];
	[expressionDescription setExpression:maxExpression];
	[expressionDescription setExpressionResultType:NSInteger64AttributeType];
	
	// Set the request's properties to fetch just the property represented by the expressions.
	[request setPropertiesToFetch:[NSArray arrayWithObject:expressionDescription]];
	
	// Execute the fetch.
	NSError *error;
	NSArray *objects = [managedObjectContext executeFetchRequest:request error:&error];
	if (objects == nil) {
		// Handle the error.
		
	} else {
		if ([objects count] > 0) {
			
			result = [[[objects objectAtIndex:0] valueForKey:[NSString stringWithFormat:@"max%@", keyName]] intValue];
			
		}
		
	}
	
	[expressionDescription release];
	[request release];
	return result;
	
	
}

Rough initial plist to Core Data example

- (void)applicationDidFinishLaunching:(UIApplication *)application {    
    
    // Override point for customization after app launch
	[self createEditableCopyOfDatabaseIfNeeded];
	UIView *backgroundView = [[UIView alloc] initWithFrame: window.frame];
	backgroundView.backgroundColor = [UIColor colorWithPatternImage:[UIImage imageNamed:@"background.png"]];
	[window addSubview:backgroundView];
	[backgroundView release];
	[window addSubview:tabcontroller.view];

	
	[window makeKeyAndVisible];
	
	// TODO implement fetching of most recent records
	int maxNews = [self getMaxUpdated:@"News" key:@"updated"];
	int maxOccasion = [self getMaxUpdated:@"Occasion" key:@"updated"];
	
	NSLog([NSString stringWithFormat:@"max news timestamp %d", maxNews]);
	self.lastNews = [NSString stringWithFormat:@"%d", maxNews];
	NSLog([NSString stringWithFormat:@"max news timestamp %@", self.lastNews]);
	NSLog([NSString stringWithFormat:@"max event timestamp %d", maxOccasion]);
	self.lastOccasion = [NSString stringWithFormat:@"%d", maxOccasion];
	[NSThread detachNewThreadSelector: @selector(syncNewsFeed:)
							 toTarget: self withObject: self];
	[NSThread detachNewThreadSelector: @selector(syncOccasionFeed:)
							 toTarget: self withObject: self];
	//[self syncOccasionFeed];
	
}

/**
 syncNewsFeed: check for updates to the news feed
 */

- (void)syncNewsFeed:(id)sender {
	
    NSAutoreleasePool *newsPool = [[NSAutoreleasePool alloc] init];
	NSLog(@"fetching news");
	NSDictionary *dict = [NSDictionary dictionaryWithContentsOfURL:[NSURL URLWithString:[NSString stringWithFormat:@"http://%@/stories.plist?last=%@", SERVER, self.lastNews]]];
	[self performSelectorOnMainThread:@selector(updateNewsData:) withObject:dict waitUntilDone:YES];
	[newsPool release];
	
    [NSThread exit];
}

- (void)updateNewsData:(id)dictionary {
	if (dictionary == nil) {
		return;
	}
	NSDictionary *dict = dictionary;
	NSLog(@"count: %@", [NSString stringWithFormat:@"%d", [dict count]]);
	/*for (id key in dict) {
		NSLog(@"key: %@, value: %@", key, [dict objectForKey:key]);
	}*/
	NSArray *storyIDs = [[dict allKeys]
						 sortedArrayUsingFunction:intSort context:NULL];
	
	// create the fetch request to get all Stories matching the IDs
	[self managedObjectContext];
	NSFetchRequest *fetchRequest = [[[NSFetchRequest alloc] init] autorelease];
	NSEntityDescription *entity = [NSEntityDescription entityForName:@"News" inManagedObjectContext:managedObjectContext];
	[fetchRequest setEntity: entity];
	[fetchRequest setPredicate: [NSPredicate predicateWithFormat: @"(storyId IN %@)", storyIDs]];
	
	// make sure the results are sorted as well
	[fetchRequest setSortDescriptors: [NSArray arrayWithObject:
									   [[[NSSortDescriptor alloc] initWithKey: @"storyId"
																	ascending:YES] autorelease]]];
	NSError *error;
	NSArray *storiessMatchingNames = [managedObjectContext
									   executeFetchRequest:fetchRequest error:&error];
	
	NSEnumerator *newStoryIterator = [storyIDs objectEnumerator];
	NSEnumerator *existingStoryIterator = [storiessMatchingNames objectEnumerator];
	
	// iterate though the sorted arrays updating existing records or adding new ones
	News *existingStory;
	existingStory = [existingStoryIterator nextObject];
	id newStory;
	NSManagedObject *newMO;
	NSLog(@"existing story count: %@", [NSString stringWithFormat:@"%d", [storyIDs count]]);
	while (newStory = [newStoryIterator nextObject]) {
		if ((existingStory != nil) & ([newStory intValue] == [existingStory.storyId intValue])) {
			NSLog(@"newStory %@ existingStory %@", newStory, [existingStory storyId]);
			// update the story with the new version
			[existingStory setValuesForKeysWithDictionary:[dict objectForKey:newStory]];
			existingStory = [existingStoryIterator nextObject];
		} else {
			NSLog(@"newStory %@", newStory);
			newMO = [[NSManagedObject alloc] initWithEntity:entity
							 insertIntoManagedObjectContext:managedObjectContext];
			
			[newMO setValuesForKeysWithDictionary:[dict objectForKey:newStory]];
			
			[newMO release];
		}

	}
}

use a default sqllite database - app delegate called in didLoad before any data sync

- (void) createEditableCopyOfDatabaseIfNeeded {
	// first, test for existence - we don't want to wipe out a user's DB
	NSFileManager *fileManager = [NSFileManager defaultManager];
	NSString *documentsDirectory = [self applicationDocumentsDirectory];
	NSString *writableDBPath = [documentsDirectory stringByAppendingPathComponent:@"USITT_2010.sqlite"];
	
	BOOL dbexists = [fileManager fileExistsAtPath:writableDBPath];
	if (!dbexists) {
		// The writable database does not exist, so copy the default to the appropriate location
		NSString *defaultDBPath = [[[NSBundle mainBundle] resourcePath] stringByAppendingPathComponent:@"USITT_2010.sqlite"];
		
		NSError *error;
		BOOL success = [fileManager copyItemAtPath:defaultDBPath toPath:writableDBPath error:&error];
		if (!success) {
			NSAssert1(0 , @"Failed to create writable database with message '%@'.", [error localizedDescription]);
		}
		
	}
}

viewController snippets

- (void)viewWillAppear:(BOOL)animated {
    [super viewWillAppear:animated];
	
	if (self.resultsController != nil) {
		return;
	}
	
	MyAppDelegate *appDelegate = (MyAppDelegate*)[[UIApplication sharedApplication] delegate];
	NSManagedObjectContext *managedObjectContext = appDelegate.managedObjectContext;
	NSFetchRequest *request = [[NSFetchRequest alloc] init];
	NSEntityDescription *entity = [NSEntityDescription entityForName:@"News" inManagedObjectContext:managedObjectContext];
	[request setEntity:entity];
	//NSPredicate *predicate = [NSPredicate predicateWithFormat:@"captured == YES"];
	//[request setPredicate:predicate];
	NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"date" ascending:NO];
	NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil];
	[request setSortDescriptors:sortDescriptors];
	[sortDescriptors release];
	[sortDescriptor release];
	
	NSFetchedResultsController *fetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:request managedObjectContext:managedObjectContext sectionNameKeyPath:nil cacheName:@"captured_list.cache"];
	fetchedResultsController.delegate = self;
	NSError *error;
	BOOL success = [fetchedResultsController performFetch:&error];
	if (!success) {
		// Handle the error.
	}
	
	self.resultsController = fetchedResultsController;
	[request release];
	[self.tableView reloadData];
	
}
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView {
    return [[self.resultsController sections] count];
}


// Customize the number of rows in the table view.
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
    return [[[self.resultsController sections] objectAtIndex:section] numberOfObjects];
}
- (void)tableView:(UITableView *)tableView willDisplayCell:(UITableViewCell *)cell forRowAtIndexPath:(NSIndexPath *)indexPath {
    if (indexPath.row == 0 || indexPath.row%2 == 0) {
        UIColor *altCellColor = [UIColor colorWithWhite:1 alpha:0.1];
        cell.backgroundColor = altCellColor;
	
    }
}
// Customize the appearance of table view cells.
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    
    static NSString *CellIdentifier = @"NewsCell";
    UILabel *mainLabel, *secondLabel;
	
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
	if (cell == nil) {
        cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier] autorelease];
        cell.accessoryType = UITableViewCellAccessoryDetailDisclosureButton;
		
        mainLabel = [[[UILabel alloc] initWithFrame:CGRectMake(40.0, 0.0, 280.0, 21.0)] autorelease];
        mainLabel.tag = 1;
        mainLabel.font = [UIFont systemFontOfSize:16.0];
        mainLabel.textAlignment = UITextAlignmentLeft;
        mainLabel.textColor = [UIColor blackColor];
        mainLabel.autoresizingMask = UIViewAutoresizingFlexibleLeftMargin | UIViewAutoresizingFlexibleHeight;
        [cell.contentView addSubview:mainLabel];
		mainLabel.backgroundColor = [UIColor clearColor];
		
        secondLabel = [[[UILabel alloc] initWithFrame:CGRectMake(0.0, 20.0, 280.0, 25.0)] autorelease];
        secondLabel.tag = 2;
        secondLabel.font = [UIFont systemFontOfSize:12.0];
        secondLabel.textAlignment = UITextAlignmentRight;
        secondLabel.textColor = [UIColor darkGrayColor];
        secondLabel.autoresizingMask = UIViewAutoresizingFlexibleLeftMargin | UIViewAutoresizingFlexibleHeight;

        [cell.contentView addSubview:secondLabel];
		secondLabel.backgroundColor = [UIColor clearColor];
	} else {
        mainLabel = (UILabel *)[cell.contentView viewWithTag:1];
        secondLabel = (UILabel *)[cell.contentView viewWithTag:2];
    }
    News *news = [self.resultsController objectAtIndexPath:indexPath];
    mainLabel.text = news.title;
    NSDateFormatter *formatter = [[[NSDateFormatter alloc] init] autorelease];
	[formatter setDateStyle:NSDateFormatterShortStyle];
	[formatter setTimeStyle:NSDateFormatterShortStyle];
	[formatter setTimeZone:[NSTimeZone timeZoneWithName:@"UTC"]];	
	
	secondLabel.text = [formatter stringFromDate:news.date];
	
    return cell;
}