What am I doing wrong with this conditional statement using a UILabel in iOS?

Question

What am I doing wrong with this conditional statement using a UILabel in Xcode?

Over simplified example, but I am trying to change the content of the UILabel in relation to text in the UILabel.

-(IBAction)answerQuestion:(id)sender{
    NSString *startingLableContent = @"Do dogs bark?";
    NSString *answer = @"Yes.";
    NSString *askAnother = @"What else do you want?";
    if (mainLable.text == startingLableContent) {
        mainLable.text = answer;
    }else if (mainLable.text == answer){
        mainLable.text = askAnother;
    }
}

How would he know to search for "Objective-C comparing strings" when he didn't realize that was what he was doing wrong? — HalR, Apr 30 '13 at 19:49
Well, it seemed natural to me if the comparison of two strings in Objective-C does not give the expected result. — Martin R, Apr 30 '13 at 19:58
@MartinR perhaps that is why you have 28k of reputation and not 4 :) — HalR, Apr 30 '13 at 20:38

HalR · Accepted Answer · 2013-04-30T19:51:30.163

1

You should compare them using isEqualToString

like this:

if ([mainLable.text isEqualToString:startingLableContent])

otherwise you are testing memory locations instead of content.

edited Apr 30 '13 at 19:51

answered Apr 30 '13 at 19:32

HalR

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Technically, you could also use `isEqual` in this case, but I wouldn't. – Marcus Adams Apr 30 '13 at 19:46

score 0 · Answer 2 · answered Apr 30 '13 at 19:32

to compare Strings in Objective-C, use isEqualToString

-(IBAction)answerQuestion:(id)sender{
    NSString *startingLableContent = @"Do dogs bark?";
    NSString *answer = @"Yes.";
    NSString *askAnother = @"What else do you want?";
    if ([startingLableContent isEqualToString:mainLable.text]) {
        mainLable.text = answer;
    }else if ([answer isEqualToString:mainLable.text]){
        mainLable.text = askAnother;
    }
}

score 0 · Answer 3 · answered Apr 30 '13 at 19:33

0

Try this:

if ([mainLable.text isEqualToString:startingLableContent]) {
// do stuff
}

answered Apr 30 '13 at 19:33

sangony

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score 0 · Answer 4 · edited Jun 20 '20 at 09:12

0

==

It turns out that you can't just say if (someString == someOtherString). It will almost always return NO.

It has to do with some stuff about where the string is stored in memory. You can use == with int's and double's and those kind of things, but with NSString's, you need to do:

`if ([mainLabel.text isEqualToString:someOtherString])`

And so, your method should look like:

-(IBAction)answerQuestion:(id)sender{
    NSString *startingLableContent = @"Do dogs bark?";
    NSString *answer = @"Yes.";
    NSString *askAnother = @"What else do you want?";
    if ([mainLable.text isEqualToString:startingLableContent]) {
        mainLable.text = answer;
    }else if ([mainLable.text isEqualToString:answer]){
        mainLable.text = askAnother;
    }
}

edited Jun 20 '20 at 09:12

Community

1
1

answered Apr 30 '13 at 19:33

Undo

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If they're both pointing to the same NSString object, `==` will return true. – Marcus Adams Apr 30 '13 at 19:34
@MarcusAdams And how often does that happen? If that happens in a real-world situation to you, I would suggest staying away from lightning storms for a while. Compilers will automatically point strings to other strings if it knows *at compile time* that it's the same string. Otherwise, well.... – Undo Apr 30 '13 at 19:36
You wouldn't be doing it if you knew at compile time that they were equal. This would be for run-time checking and there are plenty of reasons to do this. Hair's answer is correct and it was first. – Marcus Adams Apr 30 '13 at 19:45

score 0 · Answer 5 · answered Apr 30 '13 at 19:35

0

You compare the pointers, not actual strings. If you want to compare strings, consider using isEqualToString instead.

answered Apr 30 '13 at 19:35

tkroman

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What am I doing wrong with this conditional statement using a UILabel in iOS?

5 Answers5

==

if ([mainLabel.text isEqualToString:someOtherString])

`if ([mainLabel.text isEqualToString:someOtherString])`