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

1. int
2. bool
3. short
4. long
5. double
6. 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.

1. 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.
   




2. 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:
There are some alternatives to using the primitive type int, such as the reference type NSInteger, which has some nice baked in functionality of distinguishing between 32 bit and 64 bit, but not all primitive types have an alternative reference type in Objective C.


Just for fun:
In .Net they have primitive types too(I believe they call them value types), kinda. The compiler recognizes traditional primitive types and therefore lets you use the syntax

int i = 5;

But despite the compiler letting you do this, this type still maps back to System.Int32. All things in .Net are mapped back to System.Object. Everything is a reference type, but .Net lets you keep the traditional syntax instead of writing:

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





Things covered in the book

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.
This is equivalent to using "<" in most languages.

NSOrderedDescending -- The left operand is greater than the right operand.
This is equivalent to using ">" in most languages.

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.

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.

Snow Leopard has only been out since Friday, but a few people got the OS upgrade early and blogged all the good stuff. Knowing this, I'm still going to blog about the new OS from Apple.