NSArray initialization in Xcode 5

Question

I'm using Xcode 5, the problem is in the following two self.<something> assignment statement Xcode says that expected expression, and also on return statement.

- (instancetype)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {

       self.questions = [NSArray arrayWithObjects: @"From what is cognac made?", @"What is 7+7?", @"What is the capital of Vermont?",nil];

       self.answers = [NSArray arrayWithObjects: @"Grapes",@"14",@"Montpelier",nil]; 

   }
   return self;
}

inside init method don't use self.questions , always use the baking variable _question = — Arun, Jul 22 '14 at 09:14
@trojanfoe well you should use the `_propertyName` and not the `self.propertyname` in init and dealloc since this will make sure KVO will not get fired and makes is more thread save. — rckoenes, Jul 22 '14 at 09:33
guys i think that was xCode issue, when i copy pasted this code it generated this exception, but now when i manually type it there is no issue — Muhammad Waqas, Jul 22 '14 at 09:35
@trojanfoe that is wrong if i type that means works perfect so don't copy and paste just type will solve your problem — Arun, Jul 22 '14 at 09:35
@rckoenes Obviously you need to write code that avoids side-effects, and one way is to avoid the use of setter methods, however even using the instance variable you can still cause side-effects by calling methods on the object when the object is not fully initialised. So there is no blanket-rule about using `self` within `init`, just that you need to understand it. However this is not what this question is about. — trojanfoe, Jul 22 '14 at 09:40
@trojanfoe same my point, i'm telling everyone so that if same problem occurs u can also remind this perspective :) — Muhammad Waqas, Jul 22 '14 at 09:42
iOS_Developer/Spynet: Sorry I have no idea what you are talking about. — trojanfoe, Jul 22 '14 at 09:44

score 1 · Answer 1 · edited May 23 '17 at 12:27

1

When writing the init methods of your code, don't access your instance variables like self.<something> you should be doing it using the direct access way of _<something so change the

self.questions = [NSArray arrayWithObjects: @"From what is cognac made?", @"What is 7+7?", @"What is the capital of Vermont?",nil];

self.answers = [NSArray arrayWithObjects: @"Grapes",@"14",@"Montpelier",nil];

too

_questions = [NSArray arrayWithObjects: @"From what is cognac made?", @"What is 7+7?", @"What is the capital of Vermont?",nil];

_answers = [NSArray arrayWithObjects: @"Grapes",@"14",@"Montpelier",nil];

The reason for using direct access (_<something>) over the dot notation (self.<something>) is because the dot notation can trigger other side effects such as KVO or key-value observing as you may know it by.

A good answer that may help you is on Initializing a property, dot notation

And What is the correct way of init iVar variables in presence of ARC

And Should I refer to self.property in the init method with ARC?

And Why would you use an ivar?

edited May 23 '17 at 12:27

Community

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answered Jul 22 '14 at 09:30

Popeye

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@Downvoter please leave reason for down vote so I can improve my answer. – Popeye Jul 22 '14 at 09:32
1

I wasn't the downvoter, however I expect the down vote was because your answer is not true. – trojanfoe Jul 22 '14 at 09:33
@trojanfoe please note the other questions that I read before this which seem to all say the same thing, please correct me if I am wrong and misunderstood the answers on these questions then. – Popeye Jul 22 '14 at 09:35
@trojanfoe has answer is not an answer to the question, but the answer is legit in that you should not use `self.` in `init` or `dealloc`. – rckoenes Jul 22 '14 at 09:35
@rckoenes Just so you are aware I am aware this doesn't fully answer the question however it was far to much to leave as a comment. – Popeye Jul 22 '14 at 09:36
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The issue with using property setters is that it's not obvious it can cause side-effects due to KVO and that is why instance variables are preferred in `init`/`dealloc`. However at the end of the day you must understand the effect of calling any method of your object, within `init` or otherwise, and therefore there is no rule saying "thou shalt not use `self` in `init`". The rule is "understand what calling a method (including setter) does". – trojanfoe Jul 22 '14 at 09:43
@trojanfoe OK that's fair so it is only a slight misunderstanding, I will edit my answer to include this when I get a chance. I will just add this under my original answer as an edit – Popeye Jul 22 '14 at 10:42

NSArray initialization in Xcode 5

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