Handler blocks and NSArrays - how to add to an array in a block?

Question

I want to add an NSObject to an NSMutableArray inside of a a block. In the code below, the NSLog line works fine and returns the number I expect. However, when I try to add that result to an NSArray, the array is always empty when I go to access it later.

CMStepQueryHandler  stepQueryHandler = ^(NSInteger numberOfSteps,
NSError *error) {
    NSLog(@"CMStepQueryHandler: Steps on day: %i", (int)numberOfSteps);        
    [stepsPerDay addObject:[NSNumber numberWithInt:numberOfSteps]];
};

How can I add an object to an NSMutableArray (in this case stepsPerDay) from inside of a block so that I can access it later?

Gabriele Petronella · Accepted Answer · 2013-10-07 16:04:17Z

1

The code looks fine. I suspect you forgot to initialize stepsPerDay. It should be

NSMutableArray *stepsPerDay = [NSMutableArray array];

As a non-related advice, you may also consider a more modern syntax

[stepsPerDay addObject:@(numberOfSteps)];

edited Oct 7, 2013 at 16:04

answered Oct 7, 2013 at 15:56

Gabriele Petronella

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Jackson · Accepted Answer · 2013-10-19 15:06:38Z

0

The problem was that the block would always execute the addObject after I had tried to work with the contents of the array, I guess due to the fact that the block was executed asynchronously. The solution was to have the block call a function which worked with the array and that way I could guarantee the object would deb added to the array when the function was executed.

answered Oct 19, 2013 at 15:06

Jackson

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