IOS on Lantean

Preventing crashes: JSON Parsers & Null entries!

Fri, 09 Mar 2012 16:35:06 +0000

How many times you got to parse a backend response, and tested if a given value is != nil?. Well, as it turns out, many parsers (such as JSONKit) will parse ’null’ values into an instance of NSNull. That might cause a crash… unless you write eeeverywhere… ‘!= nil && != [NSNull null]’.

So… a good idea would be to implement an NSDictionary extention, to do that. Right?. The method would look like this:

Filtering arrays with NSPredicate!

Fri, 09 Mar 2012 12:24:42 +0000

Suppose you wanna filter a collection of objects. Normally, you’d write a while loop, implement a comparison, and add the matching objects to a collection.

Well, there is an easier way!!. For the sake of this example, say you wanna filter the objects that have the BOOL ‘isEnabled set to YES. So, you could do the following:

NSPredicate* predicate = [NSPredicate predicateWithFormat:@"isEnabled == YES"]; NSArray *filteredArray = [myArray filteredArrayUsingPredicate:predicate];

Yet another powerful example of NSPredicate would be… remember ‘SELECT* WHERE FIELD IN(1, 2)’ ?. Guess what!

Memory Management Tips!

Thu, 08 Mar 2012 23:26:27 +0000

It’s REALLY recommended that you set to nil any pointer that has a reference to a released object. But it’s tedious, right?. [pointer release]; pointer = nil;.

Why don’t we use a macro instead??

#define LAWipe(x)         [x release]; x = nil;

Simple. Nice. This should help you lower down the BAD_ACCESS crashes!.

iOS Singletons

Thu, 08 Mar 2012 23:08:53 +0000

Suppose that… for whatever reason, you need to target iOS 3.x. Yes. You need to build an app that should run on any possible device. Or say that… you simply don’t wanna use GCD.

What’s the alternative to write a singleton?

+ (id)sharedInstance
{
 if(_instance = nil)
 {
 @synchronized(self)
 {
 if(_instance == nil)
 {
 _instance = [[[self class] alloc] init];
 }
 }
 }
 return _instance;
}

This is a nice alternative to the GCD option. The first time the instance is created, you’ll suffer the lag caused by the @synchronized block. But after that. it’s just an if. No context switch. No whatsoever! REALLY performant!

iOS Assertions

Thu, 08 Mar 2012 23:03:28 +0000

So… you write a new piece of code. You run it. Test it. Ship it!. And in two weeks, you end up flooded by iTunes Connect Crash Reports.

What happened?. It turned out that an attribute parsed from a backend response ended up being a NSString instead of an NSNumber. And it was only after an untested-and-specific-workflow that your application actually used that field.

How do we prevent this?. ASSERTIONS!. A good friend of mine teached me that… great software blows everywhere before getting published. If your code works perfectly… you should be scared!.

Grand Central Dispatch Singletons

Thu, 08 Mar 2012 22:46:41 +0000

So… what’s the recommended way (thread safety + performance) to implement a singleton?

Well.. it looks pretty much like this!

+ (instancetype)sharedInstance
{
 static dispatch_once_t pred;
 static Foo* bar = nil;

 dispatch_once(&pred, ^{ bar = [[Foo alloc] init]; });
 return bar;
}