Improve Load Time of Sectioned UITableView - objective-c

Question

I am displaying a UITableView modally, but it takes about two seconds for it to appear, below is the code that is holding up the transition.
ModalViewController.m:
- (void)viewDidLoad
{
[super viewDidLoad];
// get all songs from iTunes library
MPMediaQuery *songQuery = [MPMediaQuery songsQuery];
// put the songs into an array
self.songsArray = [songQuery items];
// create a sectioned array where songs are sectioned by title
self.sectionedSongsArray = [self partitionObjects:self.songsArray collationStringSelector:#selector(title)];
}
- (NSArray *)partitionObjects:(NSArray *)array collationStringSelector:(SEL)selector
{
UILocalizedIndexedCollation *collation = [UILocalizedIndexedCollation currentCollation];
NSInteger sectionCount = [[collation sectionTitles] count];
NSMutableArray *unsortedSections = [NSMutableArray arrayWithCapacity:sectionCount];
for(int i = 0; i < sectionCount; i++)
{
[unsortedSections addObject:[NSMutableArray array]];
}
for (id object in array)
{
NSInteger index = [collation sectionForObject:object collationStringSelector:selector];
[[unsortedSections objectAtIndex:index] addObject:object];
}
NSMutableArray *sections = [NSMutableArray arrayWithCapacity:sectionCount];
for (NSMutableArray *section in unsortedSections)
{
[sections addObject:[collation sortedArrayFromArray:section collationStringSelector:selector]];
}
return sections;
}
The above code works fine, but its slow to load the modal view first time, is there a better way to do this? Thanks.

Answer 1

Yeah: don’t do it in -viewDidLoad. A better place would be in the view controller’s -init or -initWithNibNamed:bundle: or whatever, and in the background. Example:
- (id)init
{
self = [super init];
if(self)
{
// ...
dispatch_async(dispatch_get_global_queue(DISPATCH_PRIORITY_DEFAULT, 0), ^{
// since it's not on the main thread, you need to create your own autorelease pool to prevent leaks
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
MPMediaQuery *songQuery = [MPMediaQuery songsQuery];
self.songsArray = [songQuery items];
self.sectionedSongsArray = [self partitionObjects:self.songsArray collationStringSelector:#selector(title)];
// UI calls have to be on the main thread, so we go back to that here
dispatch_async(dispatch_get_main_queue(), ^{
if([self isViewLoaded])
{
[self.tableView reloadData];
}
});
// this releases any objects that got autoreleased earlier in the block
[pool release];
});
}
return self;
}
Your -tableView:numberOfRowsInSection: method should of course now check whether sectionedSongsArray is non-nil and in that case return 0 (or 1 if you want to display a “loading” cell, which you probably should).