Uitableview scroll lag With Lazyloading(apple Source Code) - ios

Question

Im trying to figure out why my program runs well on simulator but not on Phone.
when i scroll my Tables it gets laggy.
ive tried everything , even removed my Images loading but still scroll lag happen.
Im using apple lazy loading source code :
this is my code :
#define kCustomRowCount 7
#interface SubCategoryViewController () <UIScrollViewDelegate>
#property (nonatomic, strong) NSMutableDictionary *imageDownloadsInProgress;
#property (nonatomic, strong) NSMutableDictionary *imageRestitleDownloadsInProgress;
#property (nonatomic, assign) int intindex;
#end
#implementation SubCategoryViewController
#pragma mark
- (void)viewDidLoad
{
[super viewDidLoad];
self.title = self.catname;
self.imageDownloadsInProgress = [NSMutableDictionary dictionary];
self.imageRestitleDownloadsInProgress = [NSMutableDictionary dictionary];
}
- (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
NSArray *allDownloads = [self.imageDownloadsInProgress allValues];
[allDownloads makeObjectsPerformSelector:#selector(cancelDownload)];
NSArray *allDownloads2 = [self.imageRestitleDownloadsInProgress allValues];
[allDownloads2 makeObjectsPerformSelector:#selector(cancelDownload)];
[self.imageDownloadsInProgress removeAllObjects];
[self.imageRestitleDownloadsInProgress removeAllObjects];
}
- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
return (interfaceOrientation != UIInterfaceOrientationPortraitUpsideDown);
}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
NSUInteger count = [self.entries count];
// if there's no data yet, return enough rows to fill the screen
if (count == 0)
{
return kCustomRowCount;
}
return count;
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *PlaceholderCellIdentifier = #"PlaceholderCell2";
NSUInteger nodeCount = [self.entries count];
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:PlaceholderCellIdentifier];
cell.contentView.translatesAutoresizingMaskIntoConstraints = NO;
UILabel *newsbody = (UILabel *)[cell.contentView viewWithTag:6];
UIImageView *uimg = (UIImageView *)[cell.contentView viewWithTag:20];
UIImageView *uimgresttile = (UIImageView *)[cell.contentView viewWithTag:23];
if (nodeCount == 0 && indexPath.row == 0)
{
if (cell == nil) {
uimg.hidden = true;
uimgresttile.hidden = true;
newsbody.hidden = true;
}
else
{
uimg.hidden = true;
uimgresttile.hidden = true;
newsbody.hidden = true;
}
return cell;
}
if (nodeCount == 0 && indexPath.row > 0)
{
cell.hidden = true;
return cell;
}
if (nodeCount > 0)
{
uimg.hidden = false;
uimgresttile.hidden = false;
newsbody.hidden = true;
NewsFetchAppRecord *appRecord = [self.entries objectAtIndex:indexPath.row];
[newsbody setText:appRecord.Body];
if (!appRecord.appIcon)
{
if (self.tableView.dragging == NO && self.tableView.decelerating == NO)
{
[self startIconDownload:appRecord forIndexPath:indexPath];
}
uimg.image = [UIImage imageNamed:#"Placeholder.png"];
}
else
{
uimg.image = appRecord.appIcon;
}
if (!appRecord.appIconrestitle)
{
if (self.tableView.dragging == NO && self.tableView.decelerating == NO)
{
[self startRestitleIconDownload:appRecord forIndexPath:indexPath];
}
uimgresttile.image = [UIImage imageNamed:#"Placeholder.png"];
}
else
{
uimgresttile.image = appRecord.appIconrestitle;
}
}
if ((unsigned long)indexPath.row == [self.entries count] - 1){
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0),
^{
NewsFetchParseOperation *p = [[NewsFetchParseOperation alloc]init];
NewsFetchAppRecord *appRecord = [self.entries objectAtIndex:indexPath.row];
p.cat = appRecord.Category;
self.intindex = self.intindex + 1;
p.index = [NSString stringWithFormat:#"%d", (int)self.intindex];
p.lastid = appRecord.ids;
[p main];
dispatch_async(dispatch_get_main_queue(), ^(void)
{
SubCategoryViewController *svc =[self.storyboard instantiateViewControllerWithIdentifier:#"SubCategory"];
NSArray *temp =[self.entries arrayByAddingObjectsFromArray:p.appRecordList];
self.entries = temp;
[self.tableView reloadData];
});
});
}
return cell;
}
-(CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *PlaceholderCellIdentifier = #"PlaceholderCell2";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:PlaceholderCellIdentifier];
[cell setNeedsUpdateConstraints];
[cell updateConstraintsIfNeeded];
cell.bounds = CGRectMake(0.0f, 0.0f, CGRectGetWidth(tableView.bounds), CGRectGetHeight(cell.bounds));
[cell setNeedsLayout];
[cell layoutIfNeeded];
CGFloat height = [cell.contentView systemLayoutSizeFittingSize:UILayoutFittingCompressedSize].height;
height += 1;
return height;
}
- (void)startIconDownload:(NewsFetchAppRecord *)appRecord forIndexPath:(NSIndexPath *)indexPath
{
NewsFetchIconDownloader *iconDownloader = [self.imageDownloadsInProgress objectForKey:indexPath];
if (iconDownloader == nil)
{
iconDownloader = [[NewsFetchIconDownloader alloc] init];
iconDownloader.newsfetchappRecord = appRecord;
[iconDownloader setCompletionHandler:^{
UITableViewCell *cell = [self.tableView cellForRowAtIndexPath:indexPath];
UIImageView *uimg = (UIImageView *)[cell.contentView viewWithTag:20];
uimg.image = appRecord.appIcon;
[self.imageDownloadsInProgress removeObjectForKey:indexPath];
}];
[self.imageDownloadsInProgress setObject:iconDownloader forKey:indexPath];
[iconDownloader startDownload];
}
}
- (void)startRestitleIconDownload:(NewsFetchAppRecord *)appRecord forIndexPath:(NSIndexPath *)indexPath
{
NewsFetchRestitleIconDownloader *ResttitleiconDownloader = [self.imageRestitleDownloadsInProgress objectForKey:indexPath];
if (ResttitleiconDownloader == nil)
{
ResttitleiconDownloader = [[NewsFetchRestitleIconDownloader alloc] init];
ResttitleiconDownloader.newsfetchappRecord = appRecord;
[ResttitleiconDownloader setCompletionHandler:^{
UITableViewCell *cell = [self.tableView cellForRowAtIndexPath:indexPath];
UIImageView *uimgresttile = (UIImageView *)[cell.contentView viewWithTag:23];
uimgresttile.image = appRecord.appIconrestitle;
[self.imageRestitleDownloadsInProgress removeObjectForKey:indexPath];
}];
[self.imageRestitleDownloadsInProgress setObject:ResttitleiconDownloader forKey:indexPath];
[ResttitleiconDownloader startDownload];
}
}
- (void)loadImagesForOnscreenRows
{
if ([self.entries count] > 0)
{
NSArray *visiblePaths = [self.tableView indexPathsForVisibleRows];
for (NSIndexPath *indexPath in visiblePaths)
{
NewsFetchAppRecord *appRecord = [self.entries objectAtIndex:indexPath.row];
if (!appRecord.appIcon)
{
[self startIconDownload:appRecord forIndexPath:indexPath];
}
}
}
}
- (void)loadRestitleImagesForOnscreenRows
{
if ([self.entries count] > 0)
{
NSArray *visiblePaths = [self.tableView indexPathsForVisibleRows];
for (NSIndexPath *indexPath in visiblePaths)
{
NewsFetchAppRecord *appRecord = [self.entries objectAtIndex:indexPath.row];
if (!appRecord.appIconrestitle)
{
[self startRestitleIconDownload:appRecord forIndexPath:indexPath];
}
}
}
}
- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate
{
if (!decelerate)
{
[self loadImagesForOnscreenRows];
[self loadRestitleImagesForOnscreenRows];
}
}
- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView
{
[self loadImagesForOnscreenRows];
[self loadRestitleImagesForOnscreenRows];
}
#end
Edit:
In iphone if i scroll the the table it will freeze and jump most of time. even when
picture loaded properly. this problem never happen in simulator and only in real device.
i read most of article here base on "uitableview" lagging. most them suggest to use asnyc
method for downloading images. im using apple lazyloading sample method so i guess images
gets downloaded other than main thread.
think i have done till now is to comment most of code section by section and still lag
happend.
i even remove most part from Storyboard , but still lag happend.

Answer 1

You should delete all of your image download methods. Delete also scrollViewDidEndDragging and scrollViewDidEndDecelerating. I don't know why your heightForRowAtIndexPath is so complicated. Is every row a different size? If not use a simple case statement with the couple of cases you've got. Different height for each row can be a drag on resources.
Now for cellForRowAtIndexPath:
If the hidden not hidden stuff you are doing is for performance you should delete all of that.
Add AFNetworking to your project. If you are using cocaopods (you should) can add it with on line in your Podfile. It's good practice when developing with iOS to use libraries and AFNetworking is the best when it comes to getting stuff like images from a network.
#import "UIImageView+AFNetworking.h"
Now all your image work is done with one line of code (AFNetworking will handle all the caching and the performance related issues and the asynchronous stuff for you):
[uimg setImageWithURL:"http://blahbahblah.com" placeholderImage:someUIIMage]