360iDev Presentation this year: As a contract iOS programmer, I spend about 80% of my time working with other people's iOS code - either working as a part of existing teams or taking over incomplete projects from developers who are no longer around. Along the way, I've gathered a list of the common mistakes I've seen people make, the open-source libraries I've seen people misuse the most, and the really simple code changes that can make huge differences in the reliability and performance of your apps. For each mistake or anti-pattern, I'll have an explanation of the issue with it, and at least one potential remedy or remediation that could be taken. This talk will have a lot of specific code examples on a number of different topics and technologies, so hopefully everyone will learn something. And hopefully at least something will save you some time. Note that this will be a very opinionated talk, and I'm quite likely to step on someone's pet pattern, so there may be fireworks.

1. "Stop it! That
Hurts!"
Common iOS Anti-Patterns
@CarlBrwn Carl Brown
Missing final vowel (blame Flickr) 2012

2. ObBio
Carl Brown (@CarlBrwn)
iOS Contractor
Teach Intro to iOS classes
Co-Organizer CocoaCoder.org
Started Mobile Programming 2004 (Palm)
Half of team (Nov. '08) that wrote
LIVESTRONG.com Calorie Tracker
2012

3. ObBio
Carl Brown (@CarlBrwn)
iOS Contractor
Teach Intro to iOS classes
Co-Organizer CocoaCoder.org
Started Mobile Programming 2004 (Palm)
Half of team (Nov. '08) that wrote
LIVESTRONG.com Calorie Tracker
2012

4. Why So Much Bad Code?
I live in Austin Texas
2012

5. Why So Much Bad Code?
"Looks like any idiot can make an App"
2012

6. Why So Much Bad Code?
I try not to travel
2012

7. Why So Much Bad Code?
Working with clients in Austin
Where SxSW implies that
any idiot can found App startup
oDesk/Elance/etc are full of idiots
2008 NDA gave idiots a running start
2012

8. Not "Bad Code"?
At least for purposes of this talk...
Braces for 'if' on next line
2012

9. Not "Bad Code"?
At least for purposes of this talk...
Braces for 'if' on next line
Singletons ([Class sharedInstance])
2012

10. Not "Bad Code"?
At least for purposes of this talk...
Braces for 'if' on next line
Singletons ([Class sharedInstance])
Dot Notation (self.foo vs [self foo])
2012

11. Not "Bad Code"?
At least for purposes of this talk...
Braces for 'if' on next line
Singletons ([Class sharedInstance])
Dot Notation (self.foo vs [self foo])
Max nested square brackets ([[[[ ]]]])
2012

12. Not "Bad Code"?
At least for purposes of this talk...
Braces for 'if' on next line
Singletons ([Class sharedInstance])
Dot Notation (self.foo vs [self foo])
Max nested square brackets ([[[[ ]]]])
ARC-less-ness (at least not yet)
2012

13. Not "Bad Code"?
At least for purposes of this talk...
Braces for 'if' on next line
Singletons ([Class sharedInstance])
Dot Notation (self.foo vs [self foo])
Max nested square brackets ([[[[ ]]]])
ARC-less-ness (at least not yet)
Lack of Unit Tests (Unfortunately)
2012

14. "Out Of Scope"
Bad Code
At least for purposes of this talk...
Wrong in any Language
Methods way too long
(Including AppDelegate)
"Stringly Typed" code
Using strings instead of types
or Classes or enums
General Programming 101 Stuff
2012

15. Notice:
All of the code you are about to see
is real.
All of it was either released to users,
sold for real money or posted online.
Variable names have been changed to
protect the guilty.
Some has been edited for brevity.
2012

16. Bad Code
while (self && [self retainCount] >= 0) {
[self release];
}
///Carl's Note: retainCount is NSUInteger
"Tier 1" Bad:
if (--retainCount == 0) [self dealloc];
- (id)initWithTarget:(id)theTarget
{
retainCount = 1;
// We do not retain
2012

17. Bad Code
while (self && [self retainCount] >= 0) {
[self release];
}
///Carl's Note: retainCount is NSUInteger
"Tier 1" Bad:
if (--retainCount == 0) [self dealloc];
- (id)initWithTarget:(id)theTarget
{
retainCount = 1;
// We do not retain
2012

18. Bad Code
while (self && [self retainCount] >= 0) {
[self release];
}
///Carl's Note: retainCount is NSUInteger
"Tier 1" Bad:
if (--retainCount == 0) [self dealloc];
- (id)initWithTarget:(id)theTarget
{
retainCount = 1;
// We do not retain
2012

19. Bad Code
while (self && [self retainCount] >= 0) {
[self release];
}
///Carl's Note: retainCount is NSUInteger
"Tier 1" Bad:
if (--retainCount == 0) [self dealloc];
- (id)initWithTarget:(id)theTarget
{
retainCount = 1;
// We do not retain
2012

20. Bad Code
while (self && [self retainCount] >= 0) {
[self release];
}
///Carl's Note: retainCount is NSUInteger
"Tier 1" Bad:
if (--retainCount == 0) [self dealloc];
- (id)initWithTarget:(id)theTarget
{
retainCount = 1;
// We do not retain
2012

21. "Tier 1" Bad Code
Completely Useless 2012

22. Tier1: D.U.I.
http://xkcd.com/323/ 2012

23. Tier1: D.U.I.
Developing Under the Influence
http://xkcd.com/323/ 2012

24. Tier1: Exhaustion
2012

25. Tier 1:
Rage
Against
the
Machine
2012

26. "Tier 2" Bad Code
"Lost In Translation" 2012

27. Method Naming
- (EDAMNote *) getNote: (NSString *)
authenticationToken : (EDAMGuid) guid : (BOOL)
withContent : (BOOL) withResourcesData :
(BOOL) withResourcesRecognition : (BOOL)
withResourcesAlternateData; // throws
EDAMUserException *, EDAMSystemException *,
EDAMNotFoundException *, TException
2012

28. Method Naming
- (EDAMNote *) getNote: (NSString *)
authenticationToken : (EDAMGuid) guid : (BOOL)
withContent : (BOOL) withResourcesData :
(BOOL) withResourcesRecognition : (BOOL)
withResourcesAlternateData; // throws
EDAMUserException *, EDAMSystemException *,
EDAMNotFoundException *, TException
@selector(getNote::::::)
2012

29. Class Naming
@interface SettingsView :
UIViewController
<UITableViewDelegate,
UITableViewDataSource,
UITextFieldDelegate>
2012

30. Don't re-init existing objects
NSArray *barItems = _tabBarController.tabBar.items;
UIImage *image = [UIImage imageNamed:@"barImage0.png"];
[[barItems objectAtIndex:0]
initWithTitle:@"Title0" image:image tag:0];
2012

31. Read Good Code
We don't expect people to write in
English before they spend a lot of time
reading it
Programming Languages should be no
different
Read Good Books and Blogs
WWDC videos and Apple Sample Code
2012

32. Read Good Code
We don't expect people to write in
English before they spend a lot of time
reading it
Programming Languages should be no
different
Read Good Books and Blogs
WWDC videos and Apple Sample Code
2012

33. Coding Style
if ([UIImagePickerController
isSourceTypeAvailable:
UIImagePickerControllerSourceTypeCamera])
if ([[UIImagePickerController
availableMediaTypesForSourceType:
picker.sourceType] containsObject:
kUTTypeMovie])
self.cameraButton.hidden = NO;
2012

34. Coding Style
if ([UIImagePickerController
isSourceTypeAvailable:
UIImagePickerControllerSourceTypeCamera])
self.title = @"Event Info";
if ([[UIImagePickerController
availableMediaTypesForSourceType:
picker.sourceType] containsObject:
kUTTypeMovie])
self.cameraButton.hidden = NO;
2012

35. Coding Style
if ([UIImagePickerController
isSourceTypeAvailable:
UIImagePickerControllerSourceTypeCamera])
self.title = @"Event Info";
if ([[UIImagePickerController
availableMediaTypesForSourceType:
picker.sourceType] containsObject:
kUTTypeMovie])
self.cameraButton.hidden = NO;
2012

36. Error vs. Exception
@try {
// perform the request
NSError *error;
return [managedObjectContext
executeFetchRequest:request
error:&error];
}
@catch (NSException *exception) {
NSLog(@"Problem Fetching: %@", exception);
}
2012

37. More NSError
- (BOOL) save {
NSError *error = nil;
BOOL res = [[self managedObjectContext]
save: &error];
if (error != nil) {
NSLog(@"Error saving data: %@", error);
}
return res;
}
2012

38. What if?
- (BOOL)writeFile:(NSString*)name
error:(NSError**)error {
if (![data writeToFile:name error:error]) {
NSString *dir=[name lastPathComponent];
if (![fileMgr fileExistsAtPath:dir]) {
[fileMgr createDirectoryAtPath:dir
error:error];
if ([data writeToFile:name error:error]) {
return YES;
}
}
return NO;
}
return YES;
}
2012

39. Tries to Write File
- (BOOL)writeFile:(NSString*)name
error:(NSError**)error {
if (![data writeToFile:name error:error]) {
NSString *dir=[name lastPathComponent];
if (![fileMgr fileExistsAtPath:dir]) {
[fileMgr createDirectoryAtPath:dir
error:error];
if ([data writeToFile:name error:error]) {
return YES;
}
}
return NO;
}
return YES;
}
2012

40. Mkdir if needed
- (BOOL)writeFile:(NSString*)name
error:(NSError**)error {
if (![data writeToFile:name error:error]) {
NSString *dir=[name lastPathComponent];
if (![fileMgr fileExistsAtPath:dir]) {
[fileMgr createDirectoryAtPath:dir
error:error];
if ([data writeToFile:name error:error]) {
return YES;
}
}
return NO;
}
return YES;
}
2012

41. Then tries writing again
- (BOOL)writeFile:(NSString*)name
error:(NSError**)error {
if (![data writeToFile:name error:error]) {
NSString *dir=[name lastPathComponent];
if (![fileMgr fileExistsAtPath:dir]) {
[fileMgr createDirectoryAtPath:dir
error:error];
if ([data writeToFile:name error:error]) {
return YES;
}
}
return NO;
}
return YES;
}
2012

42. What gets Returned?
- (BOOL)writeFile:(NSString*)name
error:(NSError**)error {
if (![data writeToFile:name error:error]) {
NSString *dir=[name lastPathComponent];
if (![fileMgr fileExistsAtPath:dir]) {
[fileMgr createDirectoryAtPath:dir
error:error];
if ([data writeToFile:name error:error]) {
return YES;
}
}
return NO;
}
return YES;
}
2012

43. So, don't check error
- (BOOL) save {
NSError *error = nil;
BOOL res = [[self managedObjectContext]
save: &error];
if (error ! = nil) {
NSLog(@"Error saving data: %@", error);
}
return res;
}
2012

44. Check Return Value
- (BOOL) save {
NSError *error = nil;
BOOL res = [[self managedObjectContext]
save: &error];
if (!res ) {
NSLog(@"Error saving data: %@", error);
}
return res;
}
2012

45. Threading...
[NSThread detachNewThreadSelector:
@selector(fetchImageOnNewThread:)
toTarget:self withObject:connDict];
-(void) fetchImageOnNewThread:(NSDictionary *) d {
_image = [UIImage imageWithData:
[NSData dataWithContentsOfURL:
[d objectForKey:@"URL"]]];
}
2012

46. Asynchronous iOS
Programming Rules
Threads are bad
Use Queues instead
Apple's Concurrency Programming
Guide*:
Page 10: "The Move Away from Threads"
Page 74: "Migrating Away from Threads"
Page 74: "Replacing Threads with
Dispatch Queues"
* http://developer.apple.com/library/ios/#documentation/General/Conceptual/ConcurrencyProgrammingGuide/Introduction/Introduction.html 2012

47. ...or Lack Thereof
-(IBAction)uploadAll {
if ([uploadQueueArray count] > 0) {
for (NSDictionary *item in uploadQueueArray) {
[self.uploader connect:[item objectForKey:@"servername"]];
[self.uploader authenticate:[item objectForKey:@"user"]
withPassword:[item objectForKey:@"pass"]];
[self.uploader uploadFile:[videoArray objectAtIndex:0]];
}
}
}
2012

48. Operation vs Dispatch
I tend to use NSOperations for:
things I'm going to do several times
things that have non-trivial complexity
2012

49. Operation vs Dispatch
I tend to use NSOperations for:
things I'm going to do several times
things that have non-trivial complexity
I tend to use dispatch_async() for things:
with less than 10 or so lines of code
done only once in the App
that won't need to change when spec changes
2012

50. Waiting
[NSThread sleepForTimeInterval:0.5];
! // wait until the operation is completed
!
[(NSConditionLock *) operation.doneLock
lockWhenCondition:kXmlOperationComplete
beforeDate:[NSDate dateWithTimeIntervalSinceNow:
kGiveUpInterval]];
2012

51. Waiting
[[NSRunLoop currentRunLoop]
runUntilDate:[NSDate
dateWithTimeIntervalSinceNow:2.0]];
- (void)main {
//Do Stuff
CFRunLoopRun();
}
-(void) finish {
CFRunLoopStop(CFRunLoopGetCurrent());
}
2012

52. Password Storage
@interface Uploads : NSManagedObject
@property (nonatomic, retain) NSString * username;
@property (nonatomic, retain) NSString * password;
@end
@implementation Uploads
@dynamic username;
@dynamic password;
@end
password.text =
[[NSUserDefaults standardUserDefaults]
valueForKey:kPasswordPreference];
2012

53. Password Storage
Use the Keychain. These will help. 2012

54. Date Stuff
monthsArray = [[NSArray alloc]
initWithObjects:NSLocalizedString(@"January",
@"January"), NSLocalizedString(@"February",
@"February"), NSLocalizedString(@"March", @"March"),
NSLocalizedString(@"April", @"April"),
NSLocalizedString(@"May", @"May"),
NSLocalizedString(@"June", @"June"),
NSLocalizedString(@"July", @"July"),
NSLocalizedString(@"August", @"August"),
NSLocalizedString(@"September",@"September"),
NSLocalizedString(@"October",@"October"),
NSLocalizedString(@"November", @"November"),
NSLocalizedString(@"December", @"December"), nil];
2012

55. Date Stuff
NSDateFormatter *dateFormatter =
[NSDateFormatter new];
monthsArray = [dateFormatter monthSymbols];
Use NSDateFormatters. But not too many. 2012

56. Careful with Caching
fetcher = [fetcherMap objectForKey:@"type"];
if (!fetcher) {
fetcher = [[Fetcher alloc] init];
[fetcherMap setValue:fetcher
forKey:@"type"];
[fetcher release];
}
[ fetcher fetchPicturesForDelegate:self
callbackMethod:@selector(picsFound:error:)];
Where's the (intermittent) crash here? 2012

57. Careful with Caching
fetcher = [ nil objectForKey:@"type"];
if (!fetcher) {
fetcher = [[Fetcher alloc] init];
[ nil setValue:fetcher
forKey:@"type"];
[fetcher release];
}
[ fetcher fetchPicturesForDelegate:self
callbackMethod:@selector(picsFound:error:)];
Cache turned out to be nil 2012

58. Careful with Caching
fetcher = [ nil objectForKey:@"type"];
if (!fetcher) {
fetcher = [[Fetcher alloc] init];
[ nil setValue:fetcher
forKey:@"type"];
[fetcher release];
}
[NSZombie fetchPicturesForDelegate:self
callbackMethod:@selector(picsFound:error:)];
So fetcher could Zombify anytime 2012

59. Don't Cache That Way
That's a paradigm from web
programming, not mobile
Good only when you have tons of
memory
and need to serve >1K req/sec
Mobile needs to be Responsive,
but that kind of memory/time tradeoff not
helpful
2012

60. "Tier 3" Bad Code
"TL;DR" 2012

61. Tags
UITableViewCell *cell = [tableView
dequeueReusableCellWithIdentifier:CellIdentifier];
UILabel *dateLabel = (UILabel *)[cell viewWithTag:1];
UIView *imageBackground = (UIView *)[cell viewWithTag:2];
UIImageView *thumbnail = (UIImageView *)[cell viewWithTag:3];
2012

62. Tags
UITableViewCell *cell = [tableView
dequeueReusableCellWithIdentifier:CellIdentifier];
UILabel *dateLabel = (UILabel *)[cell viewWithTag:1];
UIView *imageBackground = (UIView *)[cell viewWithTag:2];
UIImageView *thumbnail = (UIImageView *)[cell viewWithTag:3];
https://twitter.com/drance/status/226011326273695745 2012

63. Tags should be a Last Resort
Primarily used for:
Multiple Instances of the same Class
With the same Delegate method
2012

64. Tags should be a Last Resort
Primarily used for:
Multiple Instances of the same Class
With the same Delegate method
Like UIAlertView or UIActionSheet
2012

65. Tags should be a Last Resort
Primarily used for:
Multiple Instances of the same Class
With the same Delegate method
Like UIAlertView or UIActionSheet
also -[MKMapViewDelegate
mapView:viewForAnnotation:]
2012

66. Don't "Remember"
Core Data Results
- (void)viewDidLoad
{
self.results =
[self.fetchedResultsController fetchedObjects];
! //or
self.results = [self.managedObjectContext
executeFetchRequest:fetchRequest error:&error];
}
- (UITableViewCell *)tableView:(UITableView *)tableView
cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
cell.textLabel.text =
[[self.results objectAtIndex:indexPath.row] name];
2012

67. Ask the
NSFetchedResultsController
- (UITableViewCell *)tableView:(UITableView *)tableView
cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
cell.textLabel.text =
[self.fetchedResultsController
objectAtIndexPath:indexPath];
2012

68. Don't mix read-only and
read-write data
Imagine an App that downloads bulk
data like phonebooks or store
locations or SKUs
2012

69. Don't mix read-only and
read-write data
Imagine an App that downloads bulk
data like phonebooks or store
locations or SKUs
Now imagine that App also lets the
local user comment/favorite/rate/
review those entries
2012

70. Don't mix read-only and
read-write data
Imagine an App that downloads bulk
data like phonebooks or store
locations or SKUs
Now imagine that App also lets the
local user comment/favorite/rate/
review those entries
Now imagine that every time you
updated 400K records, you had to
preserve local modifications...
2012

71. NSOperations have Overhead
NSOperationQueue *queue = [NSOperationQueue new];
NSInvocationOperation *operation =
[[NSInvocationOperation alloc]
initWithTarget:self
selector:@selector(doSomeThing)
object:nil];
[queue addOperation:operation];
[operation release];
[queue release];
2012

72. Use GCD for one-offs
dispatch_async(dispatch_get_global_queue(DISPATCH_
QUEUE_PRIORITY_BACKGROUND, 0), ^{
[self
performSelector:@selector(doSomeThing)];
});
2012

73. "Tier 3" Bad Code
"It's a Trap!!" 2012

74. "Tier 3" Bad Code
"It's a Trap!!" 2012

75. This is my scariest slide
2012

76. This is my scariest slide
2012

77. Three20
http://twitter.com/joehewitt/status/118437722519121920 2012

78. Three20 cont.
the new Facebook for iOS marks our first
release in years without the Three20
framework.
https://www.facebook.com/notes/facebook-engineering/
under-the-hood-rebuilding-facebook-for-ios/10151036091753920 2012

79. asi-http-request
After giving it a lot of thought over the
last few weeks, I’ve decided that I’m not
going to continue working on
ASIHTTPRequest in future.
http://allseeing-i.com/%5Brequest_release%5D; 2012

80. Async != Background
- (void)viewDidLoad {
! ///Snip...
! [[NSURLConnection alloc] initWithRequest:request delegate:self];
}
- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
NSString *jsonString = [[NSString alloc]
initWithData:jsonResponse
encoding:NSUTF8StringEncoding];
for (NSDictionary *jsonDict in [jsonString JSONValue]) {
! ! //Create Object
! ! [NSEntityDescription insertNewObjectForEntityForName:@"Event"];
! }
}
AFNetworking can have this confusion 2012

81. "Rocket Engine" for
Responsive Code
2012

82. "Rocket Engine" for
Responsive Code
NSAssert(![NSThread isMainThread], @"BOOM");
2012

83. "Rocket Engine" for
Responsive Code
NSAssert(![NSThread isMainThread], @"BOOM");
WARNING: Rocket Engines
can EXPLODE in testing.
2012

84. Updating from Network
- (void)eventModelDidLoad:(NSArray *)events
{
! for (UIImageView *poster in
self.scrollView.contentView.subViews) {
[poster removeFromSuperview];
}
for (Event *event in events)
{
UIImageView *poster = [[UIImageView alloc]
initWithImage:event.image];
[eventPoster setFrame:event.frameRect];
[self.scrollView.contentView addSubview:poster];
}
}
Typical of a RESTKit Project 2012

85. Refresh Incrementally
Only Init the Subviews Where
User Might Scroll Soon
Think tableView and
dequeueReusableCellWithIdentifier
Don't Delete & Recreate
Subviews that Already Exist
2012

86. MVC
Model
2012

87. MVC
Model
Controller
View
2012

88. NMVC
Network Model (or at least "Disk")
Controller
View
2012

89. NMVC
Network Model (or at least "Disk")
Controller
View
2012

90. Networking Advice
Always* load the UI from local storage
WITHOUT WAITING or BLOCKING
Core Data or local file or something
Put up a placeholder if no data
*Except with live web pages or HTTP streaming or the like 2012

91. Networking Advice
Always* load the UI from local storage
WITHOUT WAITING or BLOCKING
Core Data or local file or something
Put up a placeholder if no data
Then start async download
*Except with live web pages or HTTP streaming or the like 2012

92. Networking Advice
Always* load the UI from local storage
WITHOUT WAITING or BLOCKING
Core Data or local file or something
Put up a placeholder if no data
Then start async download
Then put network data in local storage
*Except with live web pages or HTTP streaming or the like 2012

93. Networking Advice
Always* load the UI from local storage
WITHOUT WAITING or BLOCKING
Core Data or local file or something
Put up a placeholder if no data
Then start async download
Then put network data in local storage
Then notify the UI to refresh itself
*Except with live web pages or HTTP streaming or the like 2012

94. In Summary
Program Sober and Rested, If Possible
Leave Other Languages' Patterns
at the Door
Program Idiomatically
Don't Fight the Frameworks
Read the Fine Print
Look for Hidden Bugs
2012

95. Thank You
CarlB@PDAgent.com
@CarlBrwn
2012