bencoffman.com/blog - Objective C

Beginning iPhone 3 Development Exploring the iPhone SDK

Ben Coffman — Sat, 04 Sep 2010 21:29:55 GMT

I'm done! After a summer of surprises, swings, and roadblocks I finally finished this book, a few months behind schedule, but it's done. The last objective-C book I read was by the de facto in Mac OS X development Mr. Hillegass, (my post) I embarked on the journey of reading a book on iPhone development with the man in iPhone teaching Jeff LaMarche. Jeff is every bit as good at breaking down complex topics and making them seem easy as my .Net home skillet Scott Hanselman. In short these dudes are just smart, but they'll never tell you that and they write some good books.

This book is an easy read and provides hands on examples on how to use many of the tools provided with the iPhone SDK 3. The book is spot on with it's examples, but I'm betting new Objective-C users might have trouble following along when xCode 4 comes out. xCode 4 is quite a bit different graphically than 3 and may render the step by step instructions in this book out of date.

Overall if you are into programming on the iPhone, this is a great book to start, given you have a base working knowledge of Objective-C and an advanced understanding of programming in general.

error: expected '=', ',', ';', 'asm' or 'attribute' before 'interface'

Ben Coffman — Wed, 01 Sep 2010 21:54:31 GMT

Error Readout:
error: expected '=', ',', ';', 'asm' or '__attribute__' before 'interface'

Fix:
Added a semicolon.

Explanation:
It's important to remember that this was occurring before the interface tag, which meant it was happening in a file I was importing. In this case it was a header file with some enumerations in it that were not showing an error with a missing semi colon.

When to use the * (star) with Objective C

Ben Coffman — Sat, 12 Jun 2010 15:59:04 GMT

It's a good question.

There are some types that are not derived from NSObject, these types are called "Primitive Types." Some examples of these types are

int
bool
short
long
double
char

Sooooo basically any type that is not derived from the NSObject class is a Primitive type and does not require a "*".

Now I bet you are wondering how do I figure out if it's a primitive type or not.

An easy way is to look at the color of the syntax in xCode, is it deep blue or a sky blue? Deep blue = primitive type, but this is not entirely reliable as the standards for coloring syntax can fluctuate or change.

You can option-click on the object after you have typed it in xCode, click the little book in the upper right hand corner, when the class reference viewer comes up, look and see if it inherits from NSObject. If it doesn't it's Primitive and you don't need a "*".

Note:

int

NSInteger,

Just for fun:

value types

int i = 5;

System.Int32 i = new System.Int32(5);

Why you need to create a controller in some projects in interface builder and not in others.

Ben Coffman — Mon, 07 Jun 2010 01:05:58 GMT

When starting a new project you have the ability to select a template of premade projects. Two examples of this are
1. Navigation Based Application
2. View Based application

When these templates are selected xCode will create the appropriate base controller for you in interface builder, such as "Navigation Controller" or a "View Controller" it will also create the appropriate classes for you with some of the most commonly used delegate and datasource methods along with the appropriate methods to override.

With a new project and selecting Window-based application, you are simply creating a blank slate in which you have to create nearly everything. It's rarely advantageous to use this unless, you are creating something outside the templates offered or you are learning how all the pieces fit together.

loadView vs viewDidLoad

Ben Coffman — Sun, 09 May 2010 23:55:43 GMT

The Problem:
I was getting a white screen with no data in a UITableView on it in the iPhone simulator.

The Solution:
I had my initialization code for the array in the the "loadView" method and not the "viewDidLoad" method

Explanation:
Don't read self.view in -loadView. Only set it, don't get it. The self.view property accessor calls -loadView if the view isn't currently loaded. There's your infinite recursion. I'm guessing UITableView calls a View [pretty good guess since "view" is in the name. :)] which in turn caused my recursion.

This was a stupid little error that caused me about 30 minutes of my life due to the fact I didn't get any build errors. A simple copy and paste moved me forward.

Update: I think it might be important to distinguish the differece between loadView and viewDidLoad. (below)

loadView is the method in UIViewController that will actually load up the view and assign it to the "view" property. This is also the location that a subclass of UIViewController would override if you wanted to programatically set up the "view" property. viewDidLoad is the method that is called once the view has been loaded. This is called after loadView is called. It is a place where you can override and insert code that does further initial setup of the view once it has been loaded.

Objective C -- When to use dot notation vs bracket notation

Ben Coffman — Thu, 22 Apr 2010 00:50:48 GMT

When is the right time to use dot notation vs bracket notation in objective C, or should I not use dot notation at all? I searched around for information on this, read quite a few opinions, but this blog post seems to give an answer of why. I quote the most important part; I suggest you don't read the blog post. The post is very technical and what you really want to know is right below here. If you need to know the details, eschatology does a great job at giving them.

Most important parts of blog post:

Use dot notation to get and set objects’ state.
Use bracket notation to invoke objects’ behavior.

Eschatology -- http://eschatologist.net/blog/?p=160

A bit of a dark name for a blog, but the name doesn't affect the quality of the post.

Cocoa Programming For Mac OS X -- Objective C

Ben Coffman — Wed, 14 Apr 2010 03:10:59 GMT

I'll keep this post short. I read this book to prepare myself for iPhone development and give me a deeper understanding of Objective C. This book is probably the best book to start learning Cocoa Programming currently on the market. It gives chapter by chapter examples with exercises to follow along with. The only shortcoming of the book is that it's a bit dated to what the current xCode version is. A few of the examples might take the novice for a spin (which means it took me for a spin, sometimes a quite frustrating spin) because the step by step instructions are not exactly correct due to the fact some of the menu items have changed or been rearranged. Outside of a few minor issues, like the one I mentioned earlier, it's a pretty fun book and I would recommend it to other experienced programmers. Hopefully Mr. Hillegass will come out with a newer version.

Things covered in the book

Memory Management

Target/Actions

Helper Objects

Key-Value Coding; Key-Value Observing

NSArrayController

NSUndoManager

Archiving

Basic Core Data

Nib Files and NSWindowController

User Defaults

Using Notifications

Using Alert Panels

Localization

The list keeps going, it really covers all you need to know for having a strong hold on the basics.

Comparing Values with Objective C, Alpha Or Numeric

Ben Coffman — Sat, 02 Jan 2010 01:51:02 GMT

The Problem:
Not being able to do a simple compare in an "if statement" between two alpha or numerical statements while programing in objective C.

The Solution:
NSOrderedSame

Example Of Use:
This compares the value of "key" to the value of "support." If they are equal then you get a return value of true.

if ([key compare:Support] == NSOrderedSame)

Explanation:
For some reason Objective-C decided to make it a little bit harder to compare values. Instead of just using the traditional way "[key compare:Support]" return a true value for the if statement OR "([key compare:Support] == 0) OR "([key compare:Support] == true)" they decided to make it a little bit more complex. As demonstrated above. I'm sure the writers of Objective-C have a good reason for this, but one more level of abstraction could make Objective-C that much friendlier to it's programmers and isn't that what it's all about in the end...getting more people to develop in your language.

Some of other comparisons you might want to use are:
NSOrderedAscending -- The left operand is smaller than the right operand.
<" in most languages.
This is equivalent to using "
NSOrderedDescending -- The left operand is greater than the right operand.
This is equivalent to using ">" in most languages.

this class is not key value coding-compliant for the key managedObjectContext

Ben Coffman — Mon, 28 Sep 2009 16:55:19 GMT

Error Readout:
1st Error:
this class is not key value coding-compliant for the key managedObjectContext

2nd Error:
NSImageCell's object value must be an NSImage

Fix:
1st Error:
There is one prominent reason you could get this answer. You didn't spell your property correctly when you were binding it to....well....whatever you want to bind it to, in my case it was an Array Controller.

My problem however had nothing to do with this. When I created a new project after I upgraded to xCode 3.2 I forgot to check one very import checkbox, Create document-based application (Note: it was not a check box in older version of xCode it was a full icon selection upon creating a project). By not checking this I created a big variety of problems for myself. One of the errors occurring when I didn't check the Create document-based application, was the error this class is not key value coding-compliant for the key managedObjectContext.

2nd Error:
This error is very clear in it's issue. I was creating an entity with a property of native type binary and the compiler wanted NSImage. Grrr but I should be able to pass an image as a binary object, I would say to myself as I had urges to break my laptop and anything else in reach over my knee. My fix again was to simply create a project and remember to click Create document-based application. I know this is not your typical fix, but in case someone else runs into this issue the same way I did I hope they find this and it will be a quick and easy resolution.

Explanation:
All of this pain could have been resolved from the very beginning had I known to click Create document-based application. It was a silly little mistake that cost me a few hours. In my defense however I was under the impression of not checking Create document-based because in Hillegass's book he states that for this exercise we will not be using NSDocument, but NSPersistentDocument instead. It turns out this still means you have to check Create document-based application.

I will state that I should have known something was wrong when I didn't have a MyDocument.xib in the Resource folder after I created the project.

I've attached an image, mainly because blog posts are more fun when there is an image, but also because it shows where this one simple little check box changed my life for a hot minute.

unable to read unknown load command 0x80000022

Ben Coffman — Fri, 18 Sep 2009 02:01:43 GMT

Error Readout:
unable to read unknown load command 0x80000022

Fix:
Upgrade to xCode 3.2 with the 10.6 libraries.

Explanation:
This error doesn't do anything to your application except provide some really annoying output to your Debugger Console. File under annoying. You can get xCode 3.2 DOWNLOAD HERE for free at the apple website. It will require you to create a login.