Short and comprehensive presentation about improving app's performance on the iOS platform.

1. iOS Performance
tips and tricks to do it better
Julian Król
iOS Software Engineer @ Miquido

2. Overview
• We get more powerful devices but create more
complex apps
• We want to keep UI highly responsive
• Present valuable content ASAP

3. – Ralph Marston (http://www.brainyquote.com)
“Don't lower your expectations to meet your
performance. Raise your level of
performance to meet your expectations.”

4. Most general
Avoid blocking main thread whenever it is possible, put the hard computing to
background and on the man thread update UI
!
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
//work to be done in background (for example data parsing or retrieving)
dispatch_async(dispatch_get_main_queue(), ^{
//updating UI when the expensive work is finished on the background thread
});
});
!

5. reuseIdentifier
Probably everyone knows that but for clarity:
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
static NSString *MyIdentifier = @"CellIdentifier";
JKMyCell *cell = [tableView dequeueReusableCellWithIdentifier:MyIdentifier];
//if cell was not created so far then initialise it
if (!cell) {
cell = [[NSBundle mainBundle] loadNibNamed:@"JKMyCell" owner:nil options:nil][0];
}
//in other case only update - do not allocate it every time!
JKModelObject *obj = [self getObjectAtIndexPath:indexPath];// retrieving model object to update cell
[cell update:obj]; //update cell every time it gets called to the view
return cell;
}

6. Creation & Caching
• avoid recreation of big and slow objects,
example: NSDateFormatter and re-setting its
format
• create (reusable) objects once and reuse
whenever possible (a few date formatters
depending on number of date formats)

7. Collections and enumeration
• Chose the right collection for the job!
• Be aware of how many collections are waiting for you to play
(NSArray, NSDictionary and NSSet are not the only one,
believe me!)
• General rule: arrays (fast access by index, slow to lookup by
value, as well as in insert and delete operations);
dictionaries (quick access to object by a key), sets (quick
access by a value, efficient in delete and insert operations)
• although filteredArrayUsingPredicate method looks fancy it
is very slow!
for more details click here

8. Shadows - common mistake
• Do not add shadows in that way:
view.layer.shadowOffset = CGSizeMake(1.f, 1.f);
view.layer.shadowRadius = 10.f;
• Use bezier path instead:
view.layer.shadowPath = [[UIBezierPath bezierPathWithRect:view.bounds] CGPath];
Not convinced? Checked it with cells in UITableView
while fast scrolling :)

9. Images - general rules
!
• while adding images existing on device use UIImage
imageNamed: rather than UIImage
imageWithContentsOfFile - first one uses caching!
• [UIColor colorWithPatternImage:] - fine as long as image
is relatively small comparing to the surface it will fulfil
otherwise use UIImageView which corresponds to the
image size
• use placeholder while loading (in the background!)
content from the web

10. Network communication
• again(!), do not block main thread!
• Try some external libraries (AFNetworking highly
recommended)
• avoid synchronous calls
• cache responses if it make sense to avoid
reloading it

11. @autoreleasepool
• the whole app is in one
• in most cases you can avoid creating many
temporary objects
• if you can not, consider @autoreleasepool
(example later on)

12. Other notices
• - (BOOL)application:(UIApplication *)application
didFinishLaunchingWithOptions:(NSDictionary *)launchOptions -
do not use it to initialise the whole world,
• most of the objects, managers etc can wait with its initialisation
till the very first usage
• accessing ivars is a bit faster than properties (I personally avoid
properties)
• handle memory warning situations
• in most cases any delegate should be weak - avoid retail cycle
counts

13. PROFILER!!
For improvement testing as well as looking for
bottlenecks use profiler which is provided with
Xcode
Most useful:
!
• allocations
• time profiler
• leaks

14. It’s time for a short demo about
measuring performance
improvement with Xcode's profiler

15. Sources and inspirations
• http://www.raywenderlich.com/31166/25-ios-
app-performance-tips-tricks
• http://www.objc.io/issue-7/collections.html

16. Thanks for the
attention