Array initialization issue in Objective-C

Question

I am having an issue with inputting information from one view controller into another. This function is in the second viewcontroller and is called multiple times in the first controller as it is in a for loop and there are multiple objects I want added to the array transfer_array. The objects are of type Poi and consist of a imageLocationX, imageLocationY, and name. The reason I have the BOOL was my attempt at only initializing the array once. The Poi object is added to the array the first time the function is called and the array is empty after the function is called again.

- (id)display:(double)imageXX andY:(double)imageYY withName:(NSString *)namee ifDone:(BOOL *)donee{
    NSLog(@"````````````````````````````````````````````````````````");

    NSLog(donee ? @"Yes" : @"No");
    if(donee == NO){
        transfer_array = [[NSMutableArray alloc] init];
    }

    NSLog(@"imageX: %f",imageXX);
    NSLog(@"imageY: %f", imageYY);
    NSLog(@"name: %@", namee);

    labelPoi = [[Poi alloc] init];
    labelPoi.imageLocationX = imageXX;
    labelPoi.imageLocationY = imageYY;
    labelPoi.name = namee;
    [transfer_array addObject:labelPoi];


    NSLog(@"label.x: %f should be: %f", labelPoi.imageLocationX, imageXX);
    NSLog(@"label.y: %f should be: %f", labelPoi.imageLocationY, imageYY);
    NSLog(@"label.name: %@ should be: %@",labelPoi.name,namee);
    NSLog(@"transssssfer: %lu", (unsigned long)transfer_array.count);

    return self;
}

Here is the log from the first time the function is called:

````````````````````````````````````````````````````````
2013-07-29 13:25:52.502 App[20856:11303] No
2013-07-29 13:25:52.502 App[20856:11303] imageX: 979.008057
2013-07-29 13:25:52.503 App[20856:11303] imageY: 115.728180
2013-07-29 13:25:52.503 App[20856:11303] name: Urgent Care
2013-07-29 13:25:52.503 App[20856:11303] label.x: 979.008057 should be: 979.008057
2013-07-29 13:25:52.503 App[20856:11303] label.y: 115.728180 should be: 115.728180
2013-07-29 13:25:52.503 App[20856:11303] label.name: Urgent Care should be:  Urgent Care
2013-07-29 13:25:52.503 App[20856:11303] transfer_array.count: 1

And the second time:

2013-07-29 13:25:52.506 App[20856:11303] ````````````````````````````````````````````````````````
2013-07-29 13:25:52.506 App[20856:11303] Yes
2013-07-29 13:25:52.506 App[20856:11303] imageX: 224.485718
2013-07-29 13:25:52.506 App[20856:11303] imageY: 116.353401
2013-07-29 13:25:52.506 App[20856:11303] name: Student Health Center
2013-07-29 13:25:52.507 App[20856:11303] label.x: 224.485718 should be: 224.485718
2013-07-29 13:25:52.507 App[20856:11303] label.y: 116.353401 should be: 116.353401
2013-07-29 13:25:52.507 App[20856:11303] label.name: Student Health Center should be:  Student Health Center
2013-07-29 13:25:52.507 App[20856:11303] transfer_array.count: 0

I cannot access any of the information in the array because it is empty. Does anyone know how I can modify this so that the function will continually add the objects I want to add instead of remaining empty?

EDIT

This was how the function was called in the first view controller and this method was suggested to me by a friend

PictureViewController *newlabel = [[PictureViewController alloc] display:PointOfInterest.imageLocationX andY:PointOfInterest.imageLocationY withName:PointOfInterest.name ifDone:done];
            if(done == NO){
                done = YES;
            }

@property (nonatomic,retain)NSArray *transfer_array; in the .h file and @synthesize transfer_array; in the .m file for the second view controller — user2125844
– user2125844, Commented Jul 29, 2013 at 18:34
Put the array initialization in the init method. Then no "first time through" flag is needed. If you do use a "first time through" scheme, simply test the pointer for nil vs using a flag. And assign to self.transfer_array, but do it with an autoreleased object: self.transfer_array = [NSMutableArray array];. — Hot Licks
– Hot Licks, Commented Jul 29, 2013 at 18:41
Note that your property statement mis-declares transfer_array as NSArray. The compiler SHOULD be screaming bloody murder about this, suggesting that you have another transfer_array defined somewhere as NSMutableArray. — Hot Licks
– Hot Licks, Commented Jul 29, 2013 at 18:43
Your claim is that there is no warning message on this statement: [transfer_array addObject:labelPoi]; ?? — Hot Licks
– Hot Licks, Commented Jul 29, 2013 at 20:04

Jsdodgers · Accepted Answer · 2013-07-29 19:16:12Z

1

Although esker's answer does remove the neccessity of the done and is thus preferable, that is not where your error was located. The problem that you were having was that each time you are going through your loop, you are initializing a new instance of PictureViewController. In this new object, the array has not yet been created and thus it is (null), returning a count of 0.

What you need to do is create one instance of the viewController and then add all of the objects to it. Also, in an init method, you want to call [super init] or another version of the super's initializer or another initializer you have that calls a super initializer.

answered Jul 29, 2013 at 19:16

Jsdodgers

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3 Comments

user2125844 Over a year ago

That worked! Thank you! My last problem is still that when I try to access the array in another function, the value is returned as zero. Such as

- (void)viewDidLoad{     [super viewDidLoad];      NSLog(@"transfer_array count: %lu",(unsigned long)self.transfer_array.count);

returns 0

Jsdodgers Over a year ago

I think you want to add in your display method the following code if ((self = [super init])) {//put all code here//} return self; and put all of the code you currently have in the method inside of the if block.

user2125844 Over a year ago

I still get the count equal to 0 :/

Hot Licks · Accepted Answer · 2013-07-29 20:16:56Z

1

Sigh!! Completely remove

NSLog(donee ? @"Yes" : @"No");
if(donee == NO){
    transfer_array = [[NSMutableArray alloc] init];
}

Completely remove this, if you've added it:

// property getter for transfer_array: lazily load the object
- (NSArray *)transfer_array
{
    return (transfer_array ?: transfer_array = [[NSMutableArray alloc] init];
}

Add this:

-(id)init {
   self = [super init];
   if (self) {
       self.transfer_array = [NSMutableArray array];
   }
}

-(void)dealloc {
   self.transfer_array = nil;
   // If you are not using ARC include this line
   [super dealloc];
   // (If you're not sure, add it and then remove it if the compiler complains about it.)
}

Change all remaining occurrences of "transfer_array" to "self.transfer_array".

answered Jul 29, 2013 at 20:16

Hot Licks

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6 Comments

user2125844 Over a year ago

when I do this the count of the array inside the method is correct but the array is still empty outside of the method

Hot Licks Over a year ago

"Outside of the method" -- Do you mean in another instance of your class?? Properties are tied to class instances, not the class. This is a fundamental concept of objects you need to "internalize".

user2125844 Over a year ago

Yes, another instance of my class

Hot Licks Over a year ago

So why do you expect values in one instance of your class to miraculously appear in another instance?

user2125844 Over a year ago

Is it possible to copy the array to use in another instance?

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