Question

Goal of program: Enter numbers on a viewController. When the user hits Submit button, the data entered by user is passed on to a different class for displaying on a different viewController.

Problem: I am trying to access an instance variable (numberList) in an instance method (-(void)insertNewNumber:(Numbers *)tempNumber), but it never gives me the correct output. But when I access the same variable through a protocol method of UITableViewDataSource, I get the correct answer. I figured this by using NSLog in instance method and protocol method.

Since I have declared numberList as a property variable, I was thought that I can access it from anywhere in the program and get the correct value stored in it. But compiler returned 0 for the NSLog statements when they were called from instance method. When the NSLog statements from protocol method, showed the correct result.

Please help me understand why is this occurring and how can I add elements into an array from any method in a program.

Thank you!

Here’s the relevant code I am working on:

Numbers.h:

@interface Numbers:NSObject

@property (strong, retain) NSString *ID;
@property (strong, retain) NSInteger *number;

@end

Numbers.m

@implementation Numbers

@synthesize ID, number;

@end

DisplayNumbers.h

#import <UIKit/UIKit.h>
#import "Numbers.h"

@interface DisplayNumbers : UIViewController <UITableViewDataSource, UITableViewDelegate>

@property (strong, nonatomic) NSMutableArray *numberList;

- (void)insertNewNumber:(Numbers *)tempNumber;

@end

DisplayNumbers.m:

@implementation DisplayNumbers

@synthesize numberList;


- (void)viewDidLoad
{
    [super viewDidLoad];

    numberList = [[NSMutableArray alloc] init]; 

    Numbers *num0 = [[Numbers alloc] init];
    Numbers *num1 = [[Numbers alloc] init];

    num0.ID = [NSString stringWithFormat:@"ID 0"];
    num0.number = 1111111111;

    num1.ID = [NSString stringWithFormat:@"ID 1"];
    num0.number = 2222222222;


    [numberList addObject:num0];    
    [numberList addObject:num1];    

}

- (void)insertNewNumber:(Numbers *)tempNumber
{
    NSLog(@"numberList.count (in -(void)insetNewNumber) = %d", numberList.count);
    [numberList addObject:tempNumber];
    NSLog(@"numberList.count (in -(void)insetNewNumber) = %d", numberList.count);
}

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
    return 1;
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    NSLog(@"numberList.count (in -(NSInteger)tableView:...) = %d", numberList.count);            
    Numbers *temp = [[Numbers alloc] init];
    temp.ID = @"hi";
    temp.Number = 1234;

    [numberList addObject:temp];

    NSLog(@"numberList.count (in -(NSInteger)tableView:...) = %d", numberList.count);                
   return numberList.count;
}

@end

Edit 1: Calling of insertNewNumber:.
This method is being called from a different class.

InputNumber.h:

#import <UIKit/UIKit.h>
#import "DisplayNumbers.h"

@interface InputNumber:UIViewController

@property (retain, strong) NSInteger *enteredNumber;
-(void)enteredNumber;

@end

InputNumber.m

@implementation InputNumber

@synthesize enteredNumber;
-(void)enterNumber
{
    DisplayNumber *temp = [[DisplayNumber alloc] init];
    [temp insertNewNumber:enteredNumber];
}
@end   

Answer 1

Since you allocate your numberList in the ViewDidLoad method, be sure to call your insertNewNumber method after the call to ViewDidLoad.

I believe that

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    Numbers *temp = [[Numbers alloc] init];
    temp.ID = @"hi";
    temp.Number = 1234;
    [self insertNewNumber:temp];
   return contactList.count;
}

works, right?

If you need to call your insertNewNumber method before the call to ViewDidLoad, allocate your numberList

numberList = [[NSMutableArray alloc] init]; 

in an overloaded initWithNibName:bundle: method.