"for in" objective c empty array

Question

I came to notice that executing a for/in operation in objective c on an initialized empty NSMutableArray was not working as expected.

Simplified code is :

+(void) convertArray: (NSMutableArray*)arrayIN {

    NSMutableArray *arrayOUT = [NSMutableArray array];

    NSLog(@"is nil %d - count %d", !arrayIN, [arrayIN count]);

    for(NSObject *o in arrayIN)
        [arrayOUT addObject:[o convertToAnotherClass]];

}

Actual code is :

+(BOOL) writeTasks: (NSArray*)tasksArray {

    NSMutableArray *arr = [NSMutableArray array];
    NSLog(@"is nil %d - count %d", !arr, [arr count]);
    for(Task *t in tasksArray)
        [arr addObject:[t getDictionary]];

    NSError *error; 
    NSData *jsonData = [NSJSONSerialization dataWithJSONObject:arr options:NSJSONWritingPrettyPrinted error:&error];

    if (! jsonData) {
        NSLog(@"Got an error: %@", error);
        return NO;
    } else {
        //NSString *jsonString = [[NSString alloc] initWithData:jsonData encoding:NSUTF8StringEncoding];
        [jsonData writeToFile:path options:NSDataWritingAtomic error:nil];
        return YES;
    }
}

the suprising thing is that executing [dummyClass convertArray:[NSMutableArray array]] is showing this :

2012-06-25 13:51:34.236 Planorama[740:707] is nil 0 - count 0
2012-06-25 13:51:34.239 Planorama[740:707] -[__NSArrayM convertToAnotherClass]: unrecognized selector sent to instance 0xde9b580
(lldb)

Why ? arrayIN is empty, why is convertToAnotherClass even called ?

Your code doesn't match what you're saying. You say that arrayIN is empty, but your NSLog refers to arr which is not mentioned at all in your example? — Stephen Darlington
– Stephen Darlington, Commented Jun 25, 2012 at 12:24
Oops, I tried to give explicits name bo forgot some of them... — dvkch
– dvkch, Commented Jun 25, 2012 at 12:31

Community · Accepted Answer · 2017-05-23 10:34:26Z

1

if you use the block based enumeration it will work the way you want. Also, the output indicates that o is set to some instance of something, so you may have another problem.

Elegant way to get all objects of a specific type in an Objective-C array

Lastly, it looks like this is a static method, but your example calls it as an instance method.

edited May 23, 2017 at 10:34

CommunityBot

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answered Jun 25, 2012 at 12:24

Joshua Smith

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3 Comments

dvkch Over a year ago

I may have miswritten it but this is called correctly and compiles without a problem. The only problem I have is that even an empty array declared using [NSMutableArray array] and showing a count of 0 is iterated..

dvkch Over a year ago

I pasted the actual code. I thought it might be easier to simplify it, but it adds too much questions. So here it is !

Joshua Smith Over a year ago

yes, you are checking the length of the mutable array but iterating over the taskArray, which is passed in. the newly instantiated mutable array is, of course, 0 length but the taskArray argument appears to have length > 0 in this debugging output.

dvkch · Accepted Answer · 2012-06-25 12:44:02Z

0

As Joshua Smith pointed out : I am not checking the count of the iterated array. The iterated array was not empty and contained itself because if a mistyped line :

[tasks addObject:tasks]

instead of

[tasks addObject:task]

in a previous method..

Thanks everyone !

PS : the link of Joshua Smith is very useful ! Future readers : check it out !

answered Jun 25, 2012 at 12:44

dvkch

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