CODEWITHSUNDEEP
iosobjective-c
turbo
turbo

Reputation: 1897

stringByAppendingString not concatenating

I'm trying to take an array of strings and take each item and put it into a string format. I wrote a method to do this as I need to concatenate the listed array values into another string. For some reason I cannot get the array values to list properly, a blank string is returned.

- (NSString*)listParameters:(NSArray*)params
{
NSString *outputList = @"";

if (params) {
    for (int i=0; i<[params count]; i++) {
        NSLog(@"%@",[params objectAtIndex:i]);
        [outputList stringByAppendingString:[params objectAtIndex:i]];
        if (i < ([params count] - 1)) {
            [outputList stringByAppendingString:@", "];
        }
    }
}
NSLog(@"outputList: %@", outputList);
return outputList;
}

The first log statement properly returns a string (so there is definitely a string in the array), but the second log statement only returns "outputList: ".

I tried making outputList start as more than just an empty string which didn't work. I also tried assigning [params objectAtIndex:i] to a string then appending it, didn't work either.

I feel like I'm missing something obvious here, but I cannot get it to work.

How can I get this array of strings to print into a single string separated by commas?

Upvotes: 3

Views: 1480

Answers (3)

Cody A. Ray
Cody A. Ray

Reputation: 6027

You probably want to use a NSMutableString instead with its appendString method. NSString is immutable.

- (NSString*)listParameters:(NSArray*)params
{
    NSMutableString *outputList = [[NSMutableString alloc] init];

    if (params) {
        for (int i=0; i<[params count]; i++) {
            NSLog(@"%@",[params objectAtIndex:i]);
            [outputList appendString:[params objectAtIndex:i]];
            if (i < ([params count] - 1)) {
                [outputList appendString:@", "];
            }
        }
    }

    NSLog(@"outputList: %@", outputList);
    return outputList;
}

Upvotes: 8

Extra Savoir-Faire
Extra Savoir-Faire

Reputation: 6036

You need to assign the result of [outputList stringByAppendingString:[params objectAtIndex:i]] and [outputList stringByAppendingString:@", "] back to outputList.

It would be better still if you were using an instance of NSMutableString for outputList instead, as you're going to create a lot of autoreleased objects in that loop otherwise.

Upvotes: 4

verec
verec

Reputation: 5294

Try:

outputList = [outputList stringByAppendingString:@", "];

as stringByAppendingString works by returning a new String

Upvotes: 1

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