I have a NSMutableArray which contains a few NSString objects. How can I test if the array contains a particular string literal?
I tried [array containsObject:@"teststring"] but that doesn't work.
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5 Answers
What you're doing should work fine. For example
NSArray *a = [NSArray arrayWithObjects:@"Foo", @"Bar", @"Baz", nil];
NSLog(@"At index %i", [a indexOfObject:@"Bar"]);
Correctly logs "At index 1" for me. Two possible foibles:
indexOfObjectsendsisEqualmessages to do the comparison - you've not replaced this method in a category?- Make sure you're testing against
NSNotFoundfor failure to locate, and not (say) 0.
5 Comments
Stoto
It will not work in certain cases because it checks reference.
Mike Weller
@Stoto It does not check references. It uses
-isEqual: as the answer describes.
Fogmeister
LOL! @Stoto it sounds like you've been reading this thread devforums.apple.com/thread/168948?start=0&tstart=0
Stoto
Yes, i did :) I am sure it checks reference, but due to compiler optimization two @"Bar" string constants are basically one String (pointers pointing to the same data)
Aaron
For the record, I tested this option and it works perfectly. Apple's reference at developer.apple.com/library/ios/#documentation/Cocoa/Reference/… explicitly states that
isEqual: is used for comparisons. On NSString objects, isEqual: tests the contents of the strings.[array indexOfObject:object] != NSNotFound
Comments
Comparing against string literals only works in code examples. In the real world you often need to compare against NSString* instances in e.g. an array, in which case containsObject fails because it compares against the object, not the value.
You could add a category to your implementation which extends NS(Mutable)Array with a method to check wether it contains the string (or whatever other type you need to compare against);
@implementation NSMutableArray (ContainsString)
-(BOOL) containsString:(NSString*)string
{
for (NSString* str in self) {
if ([str isEqualToString:string])
return YES;
}
return NO;
}
@end
2 Comments
peterflynn
I don't think this is true. Apple's docs for
containsObject and indexOfObject both say each element is sent an isEqual: message, so it should work even when two different NSString objects contain the same character content.
Henrik Hartz
that is only true if both objects are NSString
You may also use a predicate:
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"SELF IN %@", theArray];
BOOL result = [predicate evaluateWithObject:theString];
Comments
for every object
[(NSString *) [array objectAtIndex:i] isEqualToString:@"teststring"];
7 Comments
Adam Wright
I downvoted because it's not the right answer. You don't need to manually iterate over the array, because indexOfObject works fine. This answer will always be slower (sending many messages, no access to internal representations), and far more cumbersome. I only downvote answers when I have myself posted another answer when it's unambiguously wrong.
bbrame
I think this is correct if the strings are not static. Equality works for static strings, but not for dynamically allocated ones.
AlBeebe
It may not be the accepted answered, but its still a valid answer. I dont think down voting it was appropriate
Stoto
The accepted answer is wrong because First of all it checks the reference which can be the same if you have string constant like in the example, but will not work if the same string will be created dynamically (coming from file, web, ...) Second, there is a containsObject: method for the same thing, so you shouldn't use indexOfObject: for this. Therefore this is the correct answer.
Fattie
it's simply wrong to use indexOfObject, this is the correct answer.
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