ios - Slow UITableView Scrolling from JSON -

my uitableview scrolls when load local json. images being loaded external url. first try loading json in viewwillappear method:

dispatch_async(dispatch_get_global_queue(dispatch_queue_priority_default,0), ^{     nsstring *filepath = [[nsbundle mainbundle] pathforresource:@"homepage" oftype:@"json"];     nserror *error = nil;     nsdata *data = [nsdata datawithcontentsoffile:filepath];     self.titlelabels = [nsjsonserialization jsonobjectwithdata:data options:kniloptions error:&error]; }); 

and in tableview (uitableviewcell *)tableview:(uitableview *)tableview cellforrowatindexpath, have following:

    hometableviewcell *cell = [tableview dequeuereusablecellwithidentifier:@"cell"];  if(cell == nil) {     [tableview registernib:[uinib nibwithnibname:@"homecell" bundle:nil] forcellreuseidentifier:@"cell"];     cell = [tableview dequeuereusablecellwithidentifier:@"cell"]; }  nsdictionary *titlelabels = [self.titlelabels objectatindex:indexpath.row]; nsstring *label = [titlelabels objectforkey:@"heading"]; nsurl *imageurl = [nsurl urlwithstring:[titlelabels objectforkey:@"image"]];  uiimage *image = [uiimage imagewithdata:[nsdata datawithcontentsofurl:imageurl]];  cell.label.text = label; cell.imageview.image = image; cell.cardview.frame = cgrectmake(10, 5, 300, 395);  return cell; 

i wondering why table view scrolling slowly. if shed light on this, appreciated.

thanks!

uiimage *image = [uiimage imagewithdata:[nsdata datawithcontentsofurl:imageurl]] 

this causing slow scrolling in app. making network call cell.imageview.image property. since calling [uiimage imagewithdata:[nsdata datawithcontentsofurl:imageurl]]; on main thread, app needs wait network call finish, can scroll farther.

the keypoint here is, doing networking calls on main thread, , touches delayed untill cells have been loaded.

this not recommended, @ all.

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a better approach :

(1). make networking call, visible cells on screen. follow tutorial -- > how make faster uitableviewcell scrolling raywenderlich

(2) apple's sample code, shows in action

(3) load images beforehand , store in array, after viewdidload