UITableView can support skimming through many rows of data, however fetching large amounts of remote data can slow down your app, use up too much memory, and bog down your web server. This is all wasteful if users aren't ever going to scroll down that far. In this episode you'll learn how to perform automatic UITableView paging using an easy technique.
Initialization
- (void)viewDidLoad {
[super viewDidLoad];
self.beers = [NSMutableArray array];
_currentPage = 0;
}
Issue HTTP Request for the current page
- (void)fetchBeers {
NSString *urlString = [NSString
stringWithFormat:@"http://localhost:3000/beers.json?page=%d",
_currentPage];
NSURL *url = [NSURL URLWithString:urlString];
NSURLRequest *request = [NSURLRequest requestWithURL:url];
AFJSONRequestOperation *operation =
[[AFJSONRequestOperation alloc] initWithRequest:request];
[operation setCompletionBlockWithSuccess:
^(AFHTTPRequestOperation *operation, id responseObject) {
NSLog(@"responseObject %@", responseObject);
_totalPages = [[responseObject
objectForKey:@"total_pages"] intValue];
for (id beerDictionary in [responseObject
objectForKey:@"beers"]) {
Beer *beer = [[Beer alloc]
initWithDictionary:beerDictionary];
if (![self.beers containsObject:beer]) {
[self.beers addObject:beer];
}
[beer release];
}
[self.tableView reloadData];
} failure:
^(AFHTTPRequestOperation *operation, NSError *error) {
NSLog(@"Error: %@", [error localizedDescription]);
[[[[UIAlertView alloc]
initWithTitle:@"Error fetching beers!"
message:@"Please try again later"
delegate:nil
cancelButtonTitle:@"OK"
otherButtonTitles:nil] autorelease] show];
}];
[operation start];
[operation release];
}
Offset number of rows
- (NSInteger)tableView:(UITableView *)tableView
numberOfRowsInSection:(NSInteger)section {
if (_currentPage == 0) {
return 1;
}
if (_currentPage < _totalPages) {
return self.beers.count + 1;
}
return self.beers.count;
}
Render the cells
- (UITableViewCell *)beerCellForIndexPath:(NSIndexPath *)indexPath {
static NSString *cellIdentifier = @"cell";
UITableViewCell *cell = [self.tableView
dequeueReusableCellWithIdentifier:cellIdentifier];
if (!cell) {
cell = [[[UITableViewCell alloc]
initWithStyle:UITableViewCellStyleSubtitle
reuseIdentifier:cellIdentifier] autorelease];
}
Beer *beer = [self.beers objectAtIndex:indexPath.row];
cell.textLabel.text = beer.name;
cell.detailTextLabel.text = beer.brewery;
return cell;
}
- (UITableViewCell *)loadingCell {
UITableViewCell *cell = [[[UITableViewCell alloc]
initWithStyle:UITableViewCellStyleDefault
reuseIdentifier:nil] autorelease];
UIActivityIndicatorView *activityIndicator =
[[UIActivityIndicatorView alloc]
initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleGray];
activityIndicator.center = cell.center;
[cell addSubview:activityIndicator];
[activityIndicator release];
[activityIndicator startAnimating];
cell.tag = kLoadingCellTag;
return cell;
}
- (UITableViewCell *)tableView:(UITableView *)tableView
cellForRowAtIndexPath:(NSIndexPath *)indexPath {
if (indexPath.row < self.beers.count) {
return [self beerCellForIndexPath:indexPath];
} else {
return [self loadingCell];
}
}
Fetching the next page
- (void)tableView:(UITableView *)tableView
willDisplayCell:(UITableViewCell *)cell
forRowAtIndexPath:(NSIndexPath *)indexPath {
if (cell.tag == kLoadingCellTag) {
_currentPage++;
[self fetchBeers];
}
}
This example is from NSScreencast Episode 8 - Automatic UITableViewPaging.