Adding 3 arrays into one array in objective-C

Question

I want to add in an array 3 different arrays .. i really don't know how it works .. i've tried several ways but none did work. Can anyone help me please ?

#import "CoursesModel.h"

@implementation CoursesModel
@synthesize courses=_courses,coursesA=_coursesA,coursesB=_coursesB,coursesC=_coursesC;

-(NSArray *) coursesA
 {
 if(!_coursesA)
 {
     _coursesA = [[NSArray alloc]initWithObjects:@"A 1",A 2",A 3", nil];
 }
 return _coursesA;
 }

-(NSArray *) coursesB
{
if(!_coursesB)
{
    _coursesB = [[NSArray alloc]initWithObjects:@"B 1",@"B 2",@"B 3", nil];
}
return _coursesB;
}

-(NSArray *) coursesC
{
if(!_coursesC)
{
    _coursesC = [[NSArray alloc]initWithObjects:@"C 1",@"C 2",@"C 3", nil];
}
return _coursesC;
}

-(NSMutableArray *) courses
{
if(!_courses)
{
    _courses = [[NSMutableArray alloc]initWithCapacity:3];
    [_courses addObject:_coursesA];
    [_courses addObject:_coursesB];
    [_courses addObject:_coursesC];
}
return _courses;
}

@end

This is the code i tried using but when i tried using the values from the array courses it did not work properly. For example, i want to call the first row from the array "coursesA" if i enter "self.courses[0][0]" it gives me this error

Terminating app due to uncaught exception 'NSRangeException', reason: '*** -[__NSArrayM objectAtIndex:]: index 0 beyond bounds for empty array'

Thanks for helping

Do you call the 3 methods that create the arrays before creating 'courses' with them? — user3577225
– user3577225, Commented Mar 20, 2015 at 0:06
this code is written in a model not in a controller .. do i need to call them ? i created an object of this class in another when and in the other class (the one of the controller) i called self.cm.courses .. do i still need to call them ? @Zero — user3783005
– user3783005, Commented Mar 20, 2015 at 0:12
Where in your code is the self.courses[0][0] line that gives you the error? — Phillip Mills
– Phillip Mills, Commented Mar 20, 2015 at 0:31
In my view controller .. created the object "CoursesModel *cm;" and used "self.cm.courses[0][0];" @PhillipMills — user3783005
– user3783005, Commented Mar 20, 2015 at 0:34
You're only showing a declaration of cm, that doesn't actually create an instance. — rdelmar
– rdelmar, Commented Mar 20, 2015 at 0:40

Phillip Mills · Accepted Answer · 2015-03-20 00:42:06Z

2

Use the property specifiers so that you invoke the appropriate getters for the arrays you're putting into courses.

E.g.:

[_courses addObject:self.coursesA];
[_courses addObject:self.coursesB];
[_courses addObject:self.coursesC];

If I make these changes to your code, clean up the @"" typos, define the matching properties, and then simply call the following...

NSLog(@"From array %@", self.courses[0][0]);

...I get "2015-03-19 20:37:34.310 Test[12205:468173] From array A 1" printed in the console.

edited Mar 20, 2015 at 0:42

answered Mar 20, 2015 at 0:25

Phillip Mills

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2 Comments

Aaron Brager Over a year ago

I don't think that's the problem. addObject: would throw an exception if they were nil.

user3783005 Over a year ago

i think i know where is the problem .. i tried to put a breakpoint on the "return _courses;" but it never went there .. it just keeps repeating the function courses again and again without returning anything .. why is that ?

William Hu · Accepted Answer · 2015-03-20 00:35:49Z

1

First, _coursesA(B & C) is nil when you called, and _courses wont insert nil.

[_courses addObject:self.coursesA];
        [_courses addObject:self.coursesB];
        [_courses addObject:self.coursesC];

Then call it in any controller:

    CoursesModel *c = [CoursesModel new];
    NSArray *a = c.courses;
    DLog(@"%@ %@",a,c.courses[0][0]);

But for your issue I guess your self.mc = nil, check it.

answered Mar 20, 2015 at 0:35

William Hu

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1 Comment

user3783005 Over a year ago

its giving me "Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSCFConstantString objectAtIndexedSubscript:]: unrecognized selector sent to instance 0x83c8' "

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