How to add an object to NSMutableArray in Objective C?

Question

NSMutableArray *tblContents =  [NSMutableArray arrayWithObjects: @"1", @"2", @"3", nil];
[tblContents addObject:txtNewTableRow.text];

My app is crashing at line 2. Error message in console is 'NSInvalidArgumentException', reason: '-[NSCFString addObject:]: unrecognized selector sent to instance xxx

BTW, it works alright if i replace arraywithobjects initialization with alloc & init!

I am simply creating a mutable array and adding an object to it. Whats the problem in there?

Thanks Sridhar Reddy

Full code: .h:

#import <UIKit/UIKit.h>

@interface TableStarterViewController : UIViewController
<UITableViewDelegate, UITableViewDataSource>
{
    NSMutableArray *tblContents;

    IBOutlet UITextField *txtNewTableRow;
    IBOutlet UITableView *tblMain;
}

@property (nonatomic, retain) NSMutableArray *tblContents;
@property (nonatomic, retain) UITextField *txtNewTableRow;
@property (nonatomic, retain) UITableView *tblMain;

-(IBAction) addRowToTable;

@end

.m:

#import "TableStarterViewController.h"

@implementation TableStarterViewController

@synthesize tblContents;
@synthesize txtNewTableRow;
@synthesize tblMain;

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    return [tblContents count];
}

- (UITableViewCell *)tableView:(UITableView *)tableView 
         cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    UITableViewCell *cell = [[UITableViewCell alloc] 
                             initWithStyle:UITableViewCellStyleDefault 
                             reuseIdentifier:@"cell"];

    cell.textLabel.text = [tblContents objectAtIndex:indexPath.row];

    return cell;
}

-(IBAction) addRowToTable
{
    [tblContents addObject:txtNewTableRow.text];

    [tblMain reloadData];
}

// Implement viewDidLoad to do additional setup after loading the view, typically from a nib.
- (void)viewDidLoad {
    tblContents =  [NSMutableArray arrayWithObjects: @"1", @"2", @"3", nil];


    [super viewDidLoad];
}

Thats all code.

Is there more code between these two lines? Your error says that tblContents contains a string object, not a mutable array. — ughoavgfhw
– ughoavgfhw, Commented Dec 19, 2010 at 0:46
This code as given is correct and should work. Something else is wrong, probably with memory management of something else in your method or object, although I admit that it's not obvious what could be happening in the space of these two lines. If the crash is 100% repeatable, it does imply that you're sending a string object the addObject message. In the debugger, try "po tblContents" at this line, and the XXX in your "instance XXX"-- is that the same address as tblContents? — Ben Zotto
– Ben Zotto, Commented Dec 19, 2010 at 2:27
I agree with quixoto's comment. You should try enabling NSZombie to debug that. cocoadev.com/index.pl?NSZombieEnabled — tia
– tia, Commented Dec 19, 2010 at 7:57
Enabled zombies and this error pops up. -[__NSArrayM addObject:]: message sent to deallocated instance But I am never releasing tblContents object. Why is it getting deallocated! — Null Head
– Null Head, Commented Dec 22, 2010 at 1:34

aepryus · Accepted Answer · 2010-12-19 01:52:29Z

2

Your are not retaining the array and it is being autoreleased before you are using it. Make sure to retain it after you get the pointer back from arrayWithObjects.

Also, it's not clear to me that arrayWithObjects will return a mutable array. Which, if not, will cause further problems.

Edit 1: Alloc and Init return an object with retain count 1; arrayWithObjects returns an object with retain count 0.

Edit 2: I pulled out Xcode and verified that [NSMutableArray arrayWithObjects:] return an NSMutableArray (or according to Xcode a __NSArrayM)

edited Dec 19, 2010 at 1:52

answered Dec 19, 2010 at 0:51

aepryus

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7 Comments

Null Head Over a year ago

Well, to keep things simple (in one line, for that) I gave that code. But actually I defined instance var in .h file. Made it a property, synthesized it and all the while, it was NSMutableArray. But as you said, there might be problems with arrayWithObjects.

aepryus Over a year ago

He is trying to access tblContents and it is showing up as a NSCFString. The only time I've seen that is when an object gets released and the memory space gets reused for a different type of object. Obviously, we don't have a lot of code. But, some how the memory is getting released and reinitialized.

aepryus Over a year ago

As far as the data type of arrayWithObjects, the documentation simply says it returns NSArray; if it does in fact return NSMutableArray, fine, but as I said, it's not clear to me what arrayWithObjects returns.

aepryus Over a year ago

Here is the documentation for NSMutableArray: developer.apple.com/library/mac/#documentation/Cocoa/Reference/… . There is no arrayWithObjects method. It is however on NSArray and lists a return type of NSArray.

Jesse Anderson Over a year ago

If tblContents is defined in the header it's funny you're not getting a warning about redeclaring it in that code. You know, 'local declaration hides instance variable' or whatever.

|

Simon at The Access Group · Accepted Answer · 2013-07-16 11:02:10Z

2

instead of,

tblContents =  [NSMutableArray arrayWithObjects: @"1", @"2", @"3", nil];

try this,

tblContents =  [NSMutableArray initWithObjects: @"1", @"2", @"3", nil];

edited Jul 16, 2013 at 11:02

Simon at The Access Group

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answered Jan 20, 2012 at 12:46

Ankur

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Comments

Null Head · Accepted Answer · 2010-12-19 02:21:53Z

0

As mentioned by aepryus, arrayWithObjects is inherited from NSArray and it might actually be returning NSArray. Hence the problem. Anyone knows how to init NSMutableArray with objects?

answered Dec 19, 2010 at 2:21

Null Head

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2 Comments

ughoavgfhw Over a year ago

When called on the NSMutableArray class, it will return an NSMutableArray. Even if it returned an NSArray, he would not get that error.

aepryus Over a year ago

I verified that [NSMutableArray arrayWithObjects:] does in fact return a NSMutableArray, so you are ok with that. The problem is that your Array is being released before you are using it somehow. Double check that the tblContents object isn't being released somewhere without being retained first.

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