Objective-c : cannot init a class object

Question

I am getting an issue cannot init a class object even after adding lines to the constructor such as

self = [super init];

or

self = [[super init] alloc];

And I am not sure what to do.

This is the specific error:

file:///%3Cunknown%3E: test failure: -[LinkedListTest testAdd] failed: *** +[NList<0x8e14> init]: cannot init a class object.

.m

@interface NList()
@property (weak, nonatomic, readwrite) NSObject *head;
@property (nonatomic,readwrite) NSInteger *size;
@end

@implementation NList
@synthesize size = _size;
- (id) init:(NSInteger *)size {
    //is this even necessary? I don't want object methods.. or do I ?
    if (self){
        _head = nil;
        _size = size;
    }
    return self;
}

.h

@interface NList : NSObject
@property (nonatomic,readonly) NSInteger *size;
@property (weak, readonly, nonatomic) NSObject *head;

- (void)add:(NSObject *)node;

@end

test class

- (void)testAdd
{
    NList *testList = [[NList init] alloc];
   // Card *testCardOne = [[Card init] alloc];
   // [testList add:(testCardOne)];
    XCTAssertNotNil(testList.head);
}

I have tried adding the line

    self = [[super init] alloc];

to the constructor to no avail.

No visible interfacce for nlist declares

or self = [super init]

complains cannot init a class object!

EDIT

I realized that it is not asking me for the size! the constructor requires a size parameter...how do I do this! Ahh [looks up docs]

Brian Tracy · Accepted Answer · 2014-04-15 01:11:30Z

5

A few things.

You need a default constructor

- (id)init {
    self = [super init];
    if (self) {
        self.head = nil;
    }
    return self;
}

Now that you have a default constructor (that calls the superclasses constructor), you need a more specific one for your purposes.

- (id)initWithSize:(int)size {
    self = [self init]; // sets head, calls super constructor.
    if (self) {
        self.size = size;
    }
    return self;
}

Edit: Note, the last one had to be in your .h file so it is visible. And also, when instantiating this class, call

NList *list = [[NList alloc] initWithSize:mySize];

answered Apr 15, 2014 at 1:11

Brian Tracy

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4 Comments

bezzoon Over a year ago

Interesting! Why does it need to be declared in the header? That seems unusual? Shouldn't it become public automatically?

Bryan Chen Over a year ago

default constructor is not required

Brian Tracy Over a year ago

@BryanChen For his purposes, I believe it is. He is doing specific initialization. Thankyou for your feedback, though.

Bryan Chen Over a year ago

without default constructor, the code behave the same. (unless setHead: is implemented with some custom logic) and I can't see any reason to have it.

Michael Dautermann · Accepted Answer · 2014-04-15 01:05:19Z

3

You're a little backwards.

How about:

NList *testList = [[NList alloc] init:SIZE];

where size is the SIZE init you want to use.

Alloc comes before init when you're instantiating Objective-C objects.

answered Apr 15, 2014 at 1:05

Michael Dautermann

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3 Comments

bezzoon Over a year ago

NList *testList = [[NList alloc] init:2]; gives me an error No visible @interface for 'NList' declares the selector 'init:' .. = c

Michael Dautermann Over a year ago

Did you forget to add "#import "NList.h"" to the top of whatever .m file you're using NList in?

bezzoon Over a year ago

Still getting No visible @interface for 'NList' declares the selector 'init:' .. yeah I am importing!

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