Modifying an NSMutableArray inside a loop

Question

I have an NSMutableArray filled with Task objects. I want to be able to delete those whose completed property are set to YES

    NSMutableArray *allTasks = (NSMutableArray *)[[TaskStore defaultStore] allTasks];

    NSMutableArray *completedTasks;

    for (Task *task in allTasks) {
        if ([task completed]) {
            [completedTasks addObject:task];
        }
    }

    [allTasks removeObjectsInArray:completedTasks];

While debugging I noticed that the completedTasks array is always empty. Why is this?

Marcelo Alves · Accepted Answer · 2012-01-20 18:19:32Z

2

You forgot to initialize the completedTasks :

NSMutableArray *completedTasks = [NSMutableArray array];

answered Jan 20, 2012 at 18:19

Marcelo Alves

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dtuckernet · Accepted Answer · 2012-01-20 18:19:07Z

0

You haven't initialized completedTasks. You need to add this:

NSMutableArray *completedTasks = [[NSMutableArray alloc] init];

answered Jan 20, 2012 at 18:19

dtuckernet

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3 Comments

Iñigo Beitia Over a year ago

I have initialized it, just didn't include that part of the code.

dtuckernet Over a year ago

Have you verified that the for loop is actually looping through?

Iñigo Beitia Over a year ago

Yes, I stepped through it to be sure.

shannoga · Accepted Answer · 2012-01-20 18:20:51Z

0

You must initialize the array before you can use it, the initializing actually creates your array object -

To do this add This Line to create an autoreleased array (which means you dont have to release it)

NSMutableArray *completedTasks = [NSMutableArray array];

Or

 NSMutableArray *completedTasks = [[NSMutableArray alloc] init];

But then you will have to release it by yourself [completedTasks release] when you are not using it any moere (unless you are using ARC).

This will create your array object.

Shani

edited Jan 20, 2012 at 18:20

answered Jan 20, 2012 at 18:18

shannoga

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1 Comment

shannoga Over a year ago

it could be both, [NSMutableArray array] is an autorelesed one.

Marcelo Alves · Accepted Answer · 2012-01-20 18:59:20Z

0

from NSMutableArray documentation :

This method assumes that all elements in otherArray respond to hash and isEqual:.

You can try :

 [allTasks filterUsingPredicate:[NSPredicate predicateWithFormat:@"completed = %@", [NSNumber numberWithBool:YES]]]

answered Jan 20, 2012 at 18:59

Marcelo Alves

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