iOS count returns 0 after adding an object to NSMutableArray?

ArtOfWarfare · Sep 3, 2011

clippings is an ivar declared as a pointer to an NSMutableArray.

Here's the code in -(void)viewWillAppear

BOOL)animated

Code:

clippings = [[[[NSUserDefaults standardUserDefaults] arrayForKey:@"clippings"] mutableCopy] retain];
if ([clippings count] == 0) [clippings addObject:[UIPasteboard generalPasteboard].string];
else [clippings insertObject:[UIPasteboard generalPasteboard].string atIndex:0];
NSLog(@"Added an object to clippings.");
NSLog(@"Number of clippings: %i", [clippings count]);

And the output that is logged is:

Added an object to clippings.
Number of clippings: 0

What am I doing wrong here? I know that [UIPasteboard generalPasteboard].string is not nil, because it's displaying what's on that paste board in a UILabel elsewhere in my program.

LostSoul80 · Sep 3, 2011

You have initialized the mutable array, right?

ArtOfWarfare · Sep 3, 2011

LostSoul80 said:
You have initialized the mutable array, right?

... no...

I changed the line where I fetch it from the NSUserDefaults to this:

Code:

clippings = [[NSMutableArray arrayWithArray:[[[NSUserDefaults standardUserDefaults] arrayForKey:@"clippings"] mutableCopy]] retain];

It works now... but it looks incredibly messy. Is there some single method that will do all this for me?

North Bronson · Sep 3, 2011

It shouldn't be necessary to retain the mutable copy. The copy gives you ownership. The retain feels redundant and would require an extra release later.

I would just:

Code:

clippings = [[[NSUserDefaults standardUserDefaults] arrayForKey: @"clippings"] mutableCopy];

if (clippings == nil)
{
    clippings = [[NSMutableArray alloc] init];
}

LostSoul80 · Sep 3, 2011

I'd go with this:

Code:

clippings = [[NSMutableArray alloc] init];
[clippings addObjectsFromArray:[[NSUserDefaults standardUserDefaults] arrayForKey: @"clippings"]];

ArtOfWarfare · Sep 3, 2011

LostSoul80 said:

I like this a lot!

I changed it to this though:

Code:

clippings = [[NSMutableArray alloc] initWithArray:[[NSUserDefaults standardUserDefaults] arrayForKey:@"clippings"]];

Just one line that is about as short and easy to read as the second line of your example. And the code runs flawlessly on device.

North Bronson · Sep 7, 2011

One slight issue might be that certain objects in the Foundation framework will crash or fail if you try to initialize them with nil-values. For example, if you do something like:

Code:

NSString *file = nil;

NSArray *newArray = [[NSArray alloc] initWithContentsOfFile: file];

if (newArray)
{
    NSLog(@"good");
    
    [newArray release];
}

your code will run, but the array will be a nil-value.

On the other hand, if you try something like:

Code:

NSString *string = nil;

NSURL *newURL = [[NSURL alloc] initWithString: string];

if (newURL)
{
    NSLog(@"good");
    
    [newURL release];
}

your application will crash.

For those reasons, I would suggest it is good-form to fall into the habit of checking to see that objects are non-nil before passing them to Foundation's initWith. . . family of methods.

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iOS count returns 0 after adding an object to NSMutableArray?

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