Objective-C: Comparing normal strings and strings found in NSMutableArrays

Question

I am confused about strings (a beginner's problem, I'm afraid):

I have one NSMutableArray called Notebook. At index position 1, I have an object, which I think is a string. At least I put it into the array like this:

[NoteBook replaceObjectAtIndex:1 withObject:@"x-x-x-x"];

So far so good. If I put this into an UILabel, it will show x-x-x-x on my screen. The nightmare starts when I try to compare this string with other strings. Let's consider that I do not want to display the string x-x-x-x on my screen, but just to have a blank instead. So I thought I could achieve this by coding this:

    NSString *tempDateString;
tempDateString = [NSString stringWithFormat:@"%@",[NoteBook objectAtIndex:1]];

if (tempDateString == @"x-x-x-x") {

        UISampleLabel.text = @"";

    }

For some reason, this does not work, i.e. even if the string at position 1 of my array is 'x-x-x-x', it will still not set my UISampleLabel to nothing.

I suppose that I am getting confused with the @"" markers. When do I really need them? Why can't I simply code tempDateString = [NoteBook objectAtIndex:1]; without the formatting thing?

Any help and suggestions would be very much appreciated!

Matteo Alessani · Accepted Answer · 2011-04-09 08:59:31Z

3

You need to compare string with isEqualToString:

if ([tempDateString isEqualToString:@"x-x-x-x"]) {
  UISampleLabel.text = @"";
}

answered Apr 9, 2011 at 8:59

Matteo Alessani

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Sherm Pendley · Accepted Answer · 2011-04-09 17:35:09Z

1

In addition to the question that's been answered:

Why can't I simply code tempDateString = [NoteBook objectAtIndex:1]; without the formatting thing?

You can. Why do you think you can't?

answered Apr 9, 2011 at 17:35

Sherm Pendley

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4 Comments

Sandro Meier Over a year ago

You can. But keep in mind, that the instance you get from objectAtIndex:1 is an autorelease object. You must retain it if you want to use it outside the method. ;-)

Sherm Pendley Over a year ago

Thanks, but the same is true of the instance returned from +stringWithFormat:. Besides, I'm not asking for my own benefit - I'm asking n.evermind why he thinks +stringWithFormat: is required in the above. His answer might reveal a misconception we can help clear up.

n.evermind Over a year ago

Thanks for your comments. Actually, I'm still quite confused about the @"" thing. I thought I need this to indicate that we are dealing with a string, not? Is there a difference if I declare something with stringWithFormat or not?

Sherm Pendley Over a year ago

No, there's no difference in the end result - either way, it's a string object. @"" is just a handy shortcut that lets you declare literal string values right in your code. +stringWithFormat: is useful when you want to format a bunch of stuff into a string, as in someString = [NSString stringWithFormat:@"This:%d That:%d The other:%@", this, that, theOther]. Note that the format string that you create with @"" is just an NSString instance like any other.

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