A Successful Programmer: Reading

I’ve been thinking a long while about some of the things that have made me a successful programmer. One in particular is reading. I have read and continue to read many books. The books I read vary in topic and not all are technical. I will just to focus on technical books for now.

Even though I work professionally as an iOS developer. I keep my eyes open for useful or emerging technologies. There is something to learn from every field, technology, or language. When I find a useful technique, I adopt it into my current practices. Recently I’ve been incorporating more functional programming techniques. The idea of limiting mutable state greatly simplifies debugging later.

One of my favorite publishers is The Pragmatic Bookshelf. They publish books for programmers authored by programmers. They have books on almost any topic and at varying levels of expertise. Additionally their publications are easily affordable. They offer physical books, ebooks, and screencasts. Updated digital publications can be automatically synced with Dropbox. When I want to pick up a new technology and be assured I’m learning best practice, this is my first source. At the time of this writing, I own 31 of their books.

I also read many older books. There is much to learn from the past. One book I often reference is Design Patterns: Elements of Reusable Object-Oriented Software. Knowing good code design is fundamental to writing maintainable code. I love Don Norman’s Design of Everyday Things to better understand building usable apps. Fred Brook’s The Mythical Man Month is great for avoiding common pitfalls in managing technical projects. There are countless other classics I could mention, but these books are among my favorites.

I’ve often heard as a rule of thumb that every programmer should learn a new language every year. This is certainly not enough time to master the language. It is, however, sufficiently long to learn the unique features of the language. I personally try to read several books per year, both related and unrelated to my current work. Lately I have been studying distributed computing and Erlang/Elixir. I love parallel processing, and big data is one of the next big problems that needs to be solved. Though these studies are not directly related to iOS development, it helps me in building scalable web backends to service iOS apps.

Everyone has different learning patterns. If reading books doesn’t suit you, find other ways to learn new technologies and techniques.

As a disclaimer, I am not receiving any compensation from any publishers or authors. I have found the mentioned books useful and believe that they will benefit others.

UIStoryboard Best Practices

UIStoryboard is a hot topic right now in iOS. However, there have been many misconceptions on the topic. The first reaction to storyboards (what I have seen anyway) is that they are a panacea for all situations. Following that reaction I saw many people claim that storyboards are awful and broken. The truth is, both these ideas are wrong. During WWDC 2011 Apple may have over-promoted storyboards, thus giving the wrong impression and leading to unmet expectations. Let me correct this now: UIStoryboard is not an all-purpose solution, it is another tool for your toolbox.

My intent here is to provide the best practices for UIStoryboard. I will list my lessons learned, but there are probably more yet to learn. I expect over time that this list will expand to include other best practices for UIStoryboard.

Break your storyboard into modules

The first mistake developers have been making with storyboarding is producing large, monolithic storyboards. A single storyboard may be suitable for small apps but certainly not for large apps. Don't forget one of the key principles of programming and abstraction: decomposition. We decompose our code into modules to make them more reusable and reduce maintenance costs. The same is true for user interfaces, and it applies whether you are using UIStoryboards, XIBs, or anything else. There is an even deeper principle wanting to emerge: when code and user interfaces are decomposed together, then you have truly useful and reusable code, user interfaces, and products (you can quote me on this).

The first question to ask is "how do I identify the natural modules of my app?" Let's start with something easy. Many apps are based on a tab bar controller. Each tab is a natural module and you hence you can put them in their own storyboard. Next, if you have two tabs (or any two views for that matter) with a segue to a common view, then that common view (and its following hierarchy) is almost certainly another natural module. Once you have pruned your view hierarchy, you will probably find that each module can be given a name. For example, you may have your login storyboard, settings storyboard, about storyboard, main storyboard, etc. If you can give a fitting name to each module, then you have decomposed your hierarchy well.

Keep in mind that having a single view in a storyboard is not a bad thing. This is particularly true with table views. The power of static and prototype table view cells is very useful.

You should also note that breaking storyboards into modules makes them more friendly to version control and sharing among a team.

You don't need to convert everything at once

When you first saw storyboards, you may have had an urge to convert everything over to UIStoryboard. I know I did. Be aware that this does take time and you may not gain any immediate benefits from switching everything. Fortunately, you don't need to do it all at once. You can switch over the parts of your app that will benefit the most now. Then over time you can slowly switch out others.

Make custom UITableViewCell subclasses for prototype cells

Probably the best feature of UIStoryboard is prototype cells. They make custom table view cells easy. Prototype cells can be easily customized; however, the UITableViewCell class may not specify the IBOutlets you need. A custom subclass also gives you another advantage. You can create a -setupWith<#Object#>: method. This takes your setup code out of your table view controller and into the cell itself. This is where you can gain some great reuse.

Not only can you create custom UITableViewCell subclasses, but you can have one subclass service many prototype cells. For example, you may have a cell that takes a Person object. In one table view your cell may have main label on the left and a detail label on the right. A different table view may use the same cell but have a main label above and a detail label below. Your cell subclass handles the content, but the prototype cell handles the look and feel. Again we gain great reuse and flexibility by decomposing code and views together.

Don't forget about IBAction, IBOutlet, and IBOutletCollection

Segues are nice and can do a lot, but don't forget about the other IB fundamentals. Segues can't cross storyboards, but IBActions can. IBActions can also clean up an unnecessary spaghetti segue mess and reduce the need for custom segues. Everything has their place and their use; they are all tools at your disposal.

While on the topic of IBActions and family, I should cover encapsulation. Most, if not all, your actions and outlets do not need to be public. So, rather than put them in your public headers, put them in a class extension. See here for more details. Xcode/Interface Builder didn't handle this well in the past but now there are no problems. This keeps your interfaces much cleaner and easier for others to understand.

Don't forget about XIBs

Even though storyboards are very similar to XIBs, they still have a place. Simple, one-view modules may be better represented as XIBs. Also, XIBs can hold custom views without an associated view controller. UIStoryboard requires that view controllers be the basic unit.

You don't need to have a main storyboard

You may have noticed your app settings now has a "Main Storyboard" setting. To use UIStoryboard you are not required to use this. In fact, my latest project has neither a main storyboard nor a main XIB. It uses a programmatic UITabBarController. From there I load all my tab storyboards. The beauty of it all is that it doesn't matter whether I use UIStoryboards, XIBs, or code. All three options are flexible enough to work with each other in any combination.

Specify the name of your app delegate in main.m

As I mentioned the other day, you may need to change your main.m file if it doesn't specify your app delegate's name. It should look something like this:

UIApplicationMain(argc, argv, nil, NSStringFromClass([MyAppDelegate class]))

Put your storyboards in a category

To get one of your storyboards, you need to call +storyboardWithName:bundle:. Be wary any time you need to hard code a string for a key, especially one that can change frequently. Should you ever need to rename your storyboard, you will have to change all references to that storyboard. My favorite way to handle this is with a category. It looks something like this:

@implementation UIStoryboard (MyApp)

+ (UIStoryboard *)mainStoryboard {

    return [UIStoryboard storyboardWithName:@"MainStoryboard" bundle:nil];

}

@end

The benefit of the category approach is that if you ever rename a storyboard, you only need to change the hard coded string in one place. It also makes your code more readable.

Summary

If you take anything from this post you should remember these:

1. Decompose your code and your views.
2. UIStoryboard is a great tool, but it's not the only tool.

I hope these tips and best practices help promote proper use of UIStoryboard. I invite all my readers to let me know of other best practices they encounter.

Objective-C @property Best Practices

Now for my next rant on poor Objective-C code. Coming from other languages it's understandable that most developers don't take full advantage of the power of Objective-C 2.0. Here's a practice I hope that becomes more widespread.

Use @property

One feature of Objective-C that is underutilized is @property. The Objective-C compiler can write so much code for us, we just have to let it. Note that some of what I'm going to cover only works on the 64-bit (modern) Objective-C runtime. However, you probably won't find any situation where you need to write code for the 32-bit (legacy) runtime. The only reason we wrote legacy runtime code was because that’s what the iOS simulator used to run on (prior to iOS 4.0). That was fixed over a year ago.

Clean up your Headers

First, let's use @property to clean up our header files. The first thing to do is delete all of your ivars. Yes, delete all of them. They are no longer necessary. @synthesize will not only make your getters and setters, but it will also make your ivars. This was one of the major changes from the legacy to modern runtimes. This is nice because we don't need to be redundant about our instance variables anymore. Now, for all of your public ivars, make an equivalent @property. We'll handle the private and protected ivars in a moment. With just your public @propertys, your headers will now be much shorter and easier to read. Remember, headers are for public information. That is the whole idea behind encapsulation. You don't want your private information in your public headers. Even though I'm focusing on @propertys, you can apply the same ideas to methods too.

Categories and Class Extensions

Before handling your private and protected ivars, you need to understand categories and class extensions. If you feel comfortable using class extensions, feel free to jump to the next section.

A category is a way to extend the interface and functionality of an existing class. You declare them similarly to regular classes:

// MyClassAdditions.h

#import "MyClass.h"

@interface MyClass (CategoryName)

// Extra method declarations.

@end


// MyClassAdditions.m

#import "MyClassAdditions.h"

@implementation MyClass (CategoryName)

// Extra method implementations.

@end

Making a category is that simple. You just need to remember to #import your category when you want to use your extra methods. Class extensions, for all intents and purposes, are categories. The main differences are that only the original class can create a class extension for itself and you can declare @propertys in a class extension. So we will do just that. To create a class extension you simply create a category with no name. It will look something like this:

// MyClass.m

@interface MyClass ()

@property (nonatomic, copy) NSString * myPrivateString;

@end

With your class extension in place, you just need an associated @synthesize myPrivateString; and you're done. It's that simple. You can do this with all of your private class variables with no problems.

Protected Data

Now we are left with the protected variables. These are a little more tricky. Technically protected variables and methods don't exist with this technique. Then again “private” technically doesn't exist at all in Objective-C. The runtime won't stop you from calling private methods. Anyway, you should avoid protected data as often as possible. Sometimes that just isn't possible though. If you want a protected @property, just put it in your class extension like your private data. Then, any subclasses that need to access the protected property need to contain an identical @property in their class extensions. You will want to include some documentation about your protected @property. This does seem a little redundant to have identical @propertys, but it's bearable since Objective-C generates the important code for you. Again, this also works for methods. This is particularly nice because the @protected key word doesn't work on methods like it does ivars. One thing to note is that you can't call super in a protected method using this technique (you will get an annoying warning). If you need to make a super call, then your protected method should be placed in a private header instead. This private header should contain just the prototypes and is ONLY imported by classes that need that information.

Readonly Getters

What about when you want to make a public getter but a private setter? Objective-C can do this for you too. In your public header you can do something like this:

@property (nonatomic, copy, readonly) NSString * myPrivateString;

Then in your class extension you make a similar declaration:

@property (nonatomic, copy, readwrite) NSString * myPrivateString;

You just need to make sure the two declarations mirror each other (i.e. nonatomic and nonatomic, retain and retain, copy and copy, etc.). From there you just use @synthesize and Objective-C takes care of the rest.

Other @property Modifiers

While speaking of @property modifiers, I should take a moment to discuss them for anyone unfamiliar. You may skip to the next section if you already know the modifiers. By default an @property is atomic, assign (or weak), and readwrite. I've never found a good reason for atomic. Atomic just means that Objective-C is going to use a lock to enforce thread safety. This will make your getters and setters slower since it has to acquire and release the lock. If you are using single-threaded code this is completely unnecessary. If you are using multi-threaded code, you really should be using Grand Central Dispatch (or NSOperationQueue) to take advantage of lockless exclusion.

The next modifier is copy/retain/assign. For almost everything you do, you will use retain. It's good to know the exceptions though. When you have an NSString, NSArray, NSSet, or other object with mutable/immutable variants, you should use copy instead. If the object is immutable, it will be retained for efficiency, otherwise it will be copied.

Assign (or weak when using ARC) also has some uses. Mostly you will use it when dealing with primitives, such as BOOL or int. Since they aren't objects you can't call -copy or -retain on them. You will also use assign when you have want to avoid a retain cycle by creating a weak relationship. This is common with delegates.

You can also specify the names of your getters and setters. You specify getter=myGetterName or setter=mySetterName. This is often used with BOOLs. For example, you may create a property like this:

@property (nonatomic, assign, getter=isOn) BOOL on;

Dealloc

When writing your -dealloc methods, you may wonder how you can release your instance data without direct access to your ivars. There is only one reasonable way to do this. You should call [self setMyProperty:nil];. This will set your ivar to nil and consequently release the old value.

Exceptions

All rules have their exceptions including @property. If you need to make a custom getter or setter, you will need to create an associated ivar. Technically you can actually access synthesized ivars directly. However, Apple considers this to be a “bug” and access to synthesized ivars may disappear in the future. You can add ivars to class extensions for your private properties. Be aware, though, this is only supported on Clang/modern runtime and may require additional settings.

Benefits

Now that we've gone over all that, let's go over the benefits of these extra techniques:

1. The obvious benefit is the compiler will write your getters and setters for you. The compiler not only writes your getters and setters but also makes them Key-Value Observing (KVO) compliant. This means you can observe the changes of any property on an object. KVO is especially useful when writing Model View Controller (MVC) code. Controllers can watch model objects for any changes and update the views as appropriate.

2. You will have less memory bugs. When writing your actual code, you should always use your getters and setters instead of accessing ivars directly. This will make most of your memory management bugs disappear instantly. You won't need to remember to call retain/copy and release with your ivars. Your synthesized getters and setters will do that automatically for you.

3. Your code will be better encapsulated. I've seen too much code where I've had to guess which ivars (and methods) I could safely use due to a lack of organization and no documentation.

4. Last, but not least, your code will be more readable. Your headers won't be cluttered with private and protected data, and your implementation files won't be cluttered with standard getters and setters. Furthermore, your files will be better organized. You will know exactly where to find your public, private, and protected data.

Employ these techniques and they will serve you well. Other people who have to use your code after you with thank you too.

Credits

The ideas in this article were strongly influenced by the Apple docs, iOS Recipes Recipe 35, various WWDC videos, and a lot of personal experience (i.e. bugs).

----
Update: August 23, 2011

I have further refined and corrected this article through further study and experience on the topic, particularly ivars and custom accessors.

#define Abuse

Lately I've been encountering some terrible Objective-C code, and I have a few words to say about it. One of the first problems I've found is the overuse of #define. Don't get me wrong, #define has its place, but when it comes to constants #define should not be the first choice.

Anti-Patterns
One of the problems with #define is that it's simply a macro substitution. There is generally no type associated with the value. This makes is harder for the compiler to warn you of potential errors. Macros can also have side effects you may forget about. For example:

#define MY_STRING_CONSTANT [[NSString alloc] initWithFormat:@"Hello World!"] // Very bad.

The above example will cause a memory leak unless you remember to release the value each time. Just a side note, Apple's static analyzer will pick up this error if you turn it on. I should also mention that the following, related example is not preferable. I have actually seen this used in production code before.

#define MY_STRING_CONSTANT [NSString stringWithFormat:@"Hello World!"] // Still not great.

Numbers
With a couple anti-patterns out of the way, let's go over the proper way to define constants. You will find that it doesn't take much more effort to properly define constants. Numbers are the simplest and one of the most common, so we'll start with them. In your .m file (applies to .c or .cpp too) you will define your constant like the following:

const NSInteger kMyInt = -100;
const NSUInteger kMyUnsignedInt = 42;
const CGFloat kMyFloat = 3.14;

You could instead use 'int', 'unsigned int', and 'float' if you prefer, but the above types are generally the preferred data types. If you want to keep your constant visible to just your implementation file, then you are done. If not, you need to do one last thing. In your header file, you will need to use the following:

extern const NSInteger kMyInt;
extern const NSUInteger kMyUnsignedInt;
extern const CGFloat kMyFloat;

The reserved word 'extern' makes a promise to the compiler. You are letting the compiler know that you are not defining the value right away, but at link time, that value will exist. In this case, it's defined in your implementation file. With that in place, you are now done; your constant is defined and other classes can #import (#include for C and C++) your header file and use your number constants.

You may wonder why you can't define the constant right in your header file. If you do, you will get an error message that looks like this: "ld: duplicate symbol <Constant Name> in <File 1> and <File 2>." Generally #import handles duplicate imports properly; however, it doesn't work for constants. I figure this error is why developers unaware of 'extern' default to #define.

Enumerations
Closely related to numbers are enumerations. If you ever have a series of related number constants, you probably want an enum. For example:

// A contrived example but should get the idea across.
enum {
        kJanuary = 1,
        kFebruary = 2,
        kMarch = 3,
        kApril = 4,
        kMay = 5,
        kJune = 6,
        kJuly = 7,
        kAugust = 8,
        kSeptember = 9,
        kOctober = 10,
        kNovember = 11,
        kDecember = 12,
};

Enumerations are great for bit masks too.

// Another contrived example.
enum {
        kBit1 = 1 << 0,
        kBit2 = 1 << 1,
        kBit3 = 1 << 2,
        kBit4 = 1 << 3,
};

Enumerations are where type checking really helps. Say you are using a switch statement, the compiler can warn you if you didn't include one of your enum values as a switch case.

Strings
Strings are also very common in Cocoa programming. There is one extra detail that makes them different from numbers. At first you may want to make a constant like this:

const NSString * kMyString = @"Hello World!"; // Wrong - String Anti-Pattern 1

This is wrong for a couple different reasons. First, NSString is immutable, meaning that it can't be changed. This essentially makes it a constant by default. However, there is a big flaw with the above anti-pattern. I will first show the proper way:

NSString * const kMyString = @"Hello World!"; // Right

At first glance, you are probably wondering why 'const' is next to the constant name. The difference between the number and string examples is that the NSString is a pointer. The first string example tells the system that the value @"Hello World!" can't change, but the pointer value can change. You probably wouldn't, but you could do the following:

kMyString = @"Goodbye World!"; // Very bad, but allowed in String Anti-Pattern 1.

You didn't change the value of @"Hello World!", but you did change what kMyString pointed to. That doesn't sound like a constant at all.

By the way, the following is also permissible, but wrong.

const NSString * const kMyString = @"Hello World!"; // Wrong - String Anti-Pattern 2

This makes both the value and the pointer constant. However, the first 'const' changes the data type of the constants. None of the Cocoa frameworks accept a const NSString * (since it's redundant). This means that you will have a compiler warning anytime you try to pass your constant to a Cocoa framework method. You might do something similar with other objects, but in Objective-C, such cases should be very rare. This is something more common in C or C++.

Objects
Objects other than strings can be a little more tricky. You can't do the following:

MyObject * const kObject = [[MyObject alloc] init]; // Wrong - Object Anti-Pattern 1

The problems is the right-hand side does not evaluate to a compile time constant. Furthermore, if it was possible, it would be difficult to configure the object properly. This requires a different technique.

// Right
+ (MyObject *)MyConstObject {

        static MyObject * obj = nil;

        if (!obj) {
                obj = [[MyObject alloc] init];

        // Any other initial setup.
        }

        return obj;
}

Looking at the return type of MyObject *, you may think this has the same problem that String Anti-Pattern 1 had. This is not the case here. The original constant pointer is protected within the method; it can't be changed externally. When you call the method, you receive a copy of the object's address. You can change it if you want, but it won't affect anyone else. Naively you may want to change the return type to MyObject * const, but a const pointer doesn't affect the data type. You could do the following regardless:

MyObject * obj = [[self class] MyConstObject]; // Type MyObject * is the same as MyObject * const

One last note about object constants is that they are technically memory leaks. However, they are permissible for the same reason that singletons are permissible. What's more interesting is that Apple's latest static analyzer now flags singletons as memory leaks but still doesn't catch the above constant.

When to use #define
I should probably include a kind word about #define. If you want to use any pre-processor macros such as #if or #ifdef, then #define is your only choice. #define is also good for simple, inline functions or when you want to write some code that will do automatic renaming (see Cocoa With Love's synthesized singleton). #define has countless valuable uses, but when it comes to constants, try something else first.

Delegates and Memory Management

The iOS SDK uses the delegate pattern everywhere. Occasionally, you may want to create your own delegate protocol for some custom object. When doing so, keep in mind the subtleties of memory management. Always use @property (nonatomic, assign) rather than @property (nonatomic, retain) with delegates. It is often habit to use “retain,” but a delegate must use “assign.”

Consider the following scenario. When creating an object, its delegate is often set to “self.” Using retain as the setter policy will cause the object to retain itself. The problem is that objects (usually) don’t ever call release on delegates. Hypothetically, if a delegate is released, it’s likely to be done in -dealloc. Since the object retained itself, -dealloc will never be called. The result is a memory leak. Xcode’s static analyzer will not be able to catch this type of leak. One of the major pitfalls of reference counting is circular dependencies. The only solutions in iOS are to avoid such dependencies or force the cycle to be broken somewhere. The first option is highly preferred.

By using assign, we avoid a circular dependency. However, this doesn’t mean we can’t retain a delegate if needed. It just has to be done manually. For example: [self setDelegate:[aDelegate retain]];. This also means that the release must be done manually. Typically this can be done in -dealloc. Additionally, you may want to include a check for delegate != self. Sending [self release] in -dealloc will result in an infinite loop.