360iDev iOS AntiPatterns

"Stop it! That
Hurts!"
Common iOS Anti-Patterns

@CarlBrwn Carl Brown

Missing ﬁnal vowel (blame Flickr) 2012

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

Why So Much Bad Code?

I live in Austin Texas
2012


"Looks like any idiot can make an App"
2012


I try not to travel
2012


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

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

2012

Not "Bad Code"?
Singletons ([Class sharedInstance])

2012

Not "Bad Code"?
Dot Notation (self.foo vs [self foo])

2012

Not "Bad Code"?
Max nested square brackets ([[[[ ]]]])

2012

Not "Bad Code"?
ARC-less-ness (at least not yet)

2012

Not "Bad Code"?
ARC-less-ness (at least not yet)
Lack of Unit Tests (Unfortunately)

2012

"Out Of Scope"
Bad Code
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

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

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

"Tier 1" Bad Code

Completely Useless 2012

Tier1: D.U.I.

http://xkcd.com/323/ 2012

Tier1: D.U.I.
Developing Under the Inﬂuence

http://xkcd.com/323/ 2012

Tier1: Exhaustion

2012

Tier 1:
Rage
Against
the
Machine
2012

"Tier 2" Bad Code

"Lost In Translation" 2012

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

2012

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

@selector(getNote::::::)

2012

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

2012

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

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

Coding Style
if ([UIImagePickerController
isSourceTypeAvailable:
UIImagePickerControllerSourceTypeCamera])

if ([[UIImagePickerController
availableMediaTypesForSourceType:
picker.sourceType] containsObject:
kUTTypeMovie])

self.cameraButton.hidden = NO;

2012

Coding Style
if ([UIImagePickerController
isSourceTypeAvailable:
UIImagePickerControllerSourceTypeCamera])

self.title = @"Event Info";

if ([[UIImagePickerController
availableMediaTypesForSourceType:
picker.sourceType] containsObject:
kUTTypeMovie])

self.cameraButton.hidden = NO;

2012

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

2012

More NSError
- (BOOL) save {
NSError *error = nil;
BOOL res = [[self managedObjectContext]
save: &error];

if (error != nil) {
NSLog(@"Error saving data: %@", error);
}
return res;
}

2012

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

Tries to Write File
error:error];
return YES;
}
}
return NO;
}
return YES;
}

2012

Mkdir if needed
error:error];
return YES;
}
}
return NO;
}
return YES;
}

2012

Then tries writing again
error:error];
return YES;
}
}
return NO;
}
return YES;
}

2012

What gets Returned?
error:error];
return YES;
}
}
return NO;
}
return YES;
}

2012

So, don't check error
- (BOOL) save {
save: &error];

if (error ! = nil) {
}
return res;
}

2012

Check Return Value
- (BOOL) save {
save: &error];

if (!res ) {
}
return res;
}

2012

Threading...
[NSThread detachNewThreadSelector:
@selector(fetchImageOnNewThread:)
toTarget:self withObject:connDict];

-(void) fetchImageOnNewThread:(NSDictionary *) d {
_image = [UIImage imageWithData:
[NSData dataWithContentsOfURL:
[d objectForKey:@"URL"]]];
}

2012

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

...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

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

2012

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

Waiting
[NSThread sleepForTimeInterval:0.5];

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

2012

Waiting
[[NSRunLoop currentRunLoop]
runUntilDate:[NSDate
dateWithTimeIntervalSinceNow:2.0]];

- (void)main {
//Do Stuff
CFRunLoopRun();
}

-(void) finish {
CFRunLoopStop(CFRunLoopGetCurrent());
}

2012

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

Password Storage

Use the Keychain. These will help. 2012

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

Date Stuff

NSDateFormatter *dateFormatter =
[NSDateFormatter new];
monthsArray = [dateFormatter monthSymbols];

Use NSDateFormatters. But not too many. 2012

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

fetcher = [ nil objectForKey:@"type"];
if (!fetcher) {
[ nil setValue:fetcher
forKey:@"type"];
[fetcher release];
}

[ fetcher fetchPicturesForDelegate:self

Cache turned out to be nil 2012

fetcher = [ nil objectForKey:@"type"];
if (!fetcher) {
[ nil setValue:fetcher
forKey:@"type"];
[fetcher release];
}

[NSZombie fetchPicturesForDelegate:self

So fetcher could Zombify anytime 2012

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

"Tier 3" Bad Code

"TL;DR" 2012

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

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

Tags should be a Last Resort

Primarily used for:
Multiple Instances of the same Class
With the same Delegate method

2012


Primarily used for:
Like UIAlertView or UIActionSheet

2012


Primarily used for:
Like UIAlertView or UIActionSheet
also -[MKMapViewDelegate
mapView:viewForAnnotation:]

2012

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

Ask the
NSFetchedResultsController

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

2012

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

2012

read-write data
locations or SKUs
Now imagine that App also lets the
local user comment/favorite/rate/
review those entries

2012

read-write data
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

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

Use GCD for one-offs

dispatch_async(dispatch_get_global_queue(DISPATCH_
QUEUE_PRIORITY_BACKGROUND, 0), ^{
[self
performSelector:@selector(doSomeThing)];
});

2012

"Tier 3" Bad Code

"It's a Trap!!" 2012

This is my scariest slide

2012

Three20

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

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

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

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

"Rocket Engine" for
Responsive Code

2012

"Rocket Engine" for
Responsive Code

NSAssert(![NSThread isMainThread], @"BOOM");

2012

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

WARNING: Rocket Engines

can EXPLODE in testing.
2012

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

Refresh Incrementally

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

2012

MVC
Model

Controller

View
2012

NMVC
Network Model (or at least "Disk")

Controller

View
2012

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

Networking Advice
Then start async download


Networking Advice
Then put network data in local storage


Networking Advice
Then put network data in local storage
Then notify the UI to refresh itself


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

Thank You
CarlB@PDAgent.com
@CarlBrwn

2012

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