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Objective-c: Comparing two strings not working correctly.

Answer 1

+1 A:

Are you sure the objects in tempArray are really NSString? isEqualToString will just return false if they are some other type.

Also, could you have trailing whitespace in the strings?

James Roth 2010-06-08 15:28:23

tempArray is an NSMutableArray initialized with a @"" blank string. There is one single entry in the array. tempArray only serves as a record of what header was already added. The only items added are single letter "section index's"

Oh Danny Boy 2010-06-08 15:39:34

Answer 2

+2 A:

When the first element is not a match the return in the else branch will abort your search. If the first element is a match, the ‘then’ branch will break out of the loop (and I guess there is more code to provide a return value for that case?).

Maybe the return should replace the break in the ‘then’ branch?

Also, since you already have the string you want as [sectionInfo indexTitle], why manuall search for it? Do you just need to check whether it is in the list? Maybe something like this instead of the loop:

if ([tempArray containsObject: [sectionInfo indexTitle]]) {
    return [sectionInfo indexTitle];
} else {
    return @"<invalid>"; // or whatever
}

Chris Johnsen 2010-06-08 15:31:46

This seems to cause an infinite loop. Logically, I am unsure why.

Oh Danny Boy 2010-06-08 15:36:42

@Mr: Well, it is obvious that if you want to search the whole array you should not abort if the first one does not match. Are you sure the modified loop is “infinite”? It will definitely “spew” more “Not found” logs for each invocation.

Chris Johnsen 2010-06-08 15:55:36

I'd prefer `containsObject:` over `indexOfObject:` when only testing for the presence of an object.

Nefrubyr 2010-06-08 15:57:44

Could you explain the comparison in the if? indexTitle resolves to a character, yet you're asking for the index of tempArray according to a charecter. I don't understand how index 'A' would be logically correct. (PS: I tried it and the code compiles but does not work correctly; all headers are <invalid>"

Oh Danny Boy 2010-06-08 15:59:14

@Mr: As Nefrubyr suggested, now it uses `containsObject:`. Does it make more sense? The logic is the same as before. It is just checking to see if the object is in the array.

Chris Johnsen 2010-06-08 16:05:04

This makes sense now; but does not achieve the effect I want. I am trying to group cells by their first letter. The data comes from a database, and may change over time. Maybe I am going about this incorrectly.

Oh Danny Boy 2010-06-08 16:12:52

Answer 3

+1 A:

The first element of tempArray seems always to be an empty string. In your log, [sectionInfo indexTitle] is never an empty string.

Since you exit the method the first time you don't find something, you'll never get a true comparison.

Also I notice you are adding the not found [sectionInfo indexTitle] to your tempArray for every iteration you don't find it. Is that what you really want?

Also, if you ever did find a match, you don't return anything. You should be getting a compiler warning to say the method doesn't always return a value.

I'm kind of guessing here but I think you want something like:

    for (int i = 0; i < [tempArray count]; i++) // NB [nil count] returns 0 so your test for a nil tempArray is unnecessary
    {
        if([[sectionInfo indexTitle] isEqualToString:[tempArray objectAtIndex:i]])
        {
            NSLog(@"found");
            return [tempArray objectAtIndex:i];
        } 
        else
        {
            NSLog(@"Not found %@", [sectionInfo indexTitle]);
            NSLog(@"array %@", tempArray);
        }
    }
    [tempArray addObject:[sectionInfo indexTitle]];
    return ???? // I don't know what you want returned in this case:

Edited for the comment below:

I think I've finally understood what you are trying to do:

If you already have a section title the same as the one you are now about to deliver, you want to return nil so the section has no title. In that case, the code should look like this:

    for (int i = 0; i < [tempArray count]; i++) // NB [nil count] returns 0 so your test for a nil tempArray is unnecessary
    {
        if([[sectionInfo indexTitle] isEqualToString:[tempArray objectAtIndex:i]])
        {
            NSLog(@"found");
            return nil;
        } 
        else
        {
            NSLog(@"Not found %@", [sectionInfo indexTitle]);
            NSLog(@"array %@", tempArray);
        }
    }
    [tempArray addObject:[sectionInfo indexTitle]];
    return [sectionInfo indexTitle];

But

You can use NSMutableSet instead:

if ([tempSet containsObject: [sectionInfo indexTitle]])
{
    return nil;
}
else
{
    [tempSet addObject: [sectionInfo indexTitle]];
    return [sectionInfo indexTitle];
}

JeremyP 2010-06-08 15:59:49

This seems to work best thus far although not 100%. What I was trying to do is group my tableview alphabetically. The data comes from a SQLite DB; don't know if that makes a difference. This gives me the appropriate array "tempArray" with no duplicates, but it does not display correctly in the tableview. The tableview only shows A B and J and there are duplicate entries in each. What should I look into for grouping the the cells by their respective first letter?

Oh Danny Boy 2010-06-08 16:11:44

Both pieces of code yield the same results. They seem to add a section header for each cell. Do you have a reference to point me to to figure out how to group the cells?

Oh Danny Boy 2010-06-08 16:34:40

By the time you get to the point of having this method called, the structure of the table view is already decided. Your grouping logic needs to be implemented in your implementation of -numberOfSectionsInTableView: and -tableView:numberOfRowsInSection: The following link should help you with how to use these: http://developer.apple.com/iphone/library/documentation/UserExperience/Conceptual/TableView_iPhone/CreateConfigureTableView/CreateConfigureTableView.html#//apple_ref/doc/uid/TP40007451-CH6-SW5

JeremyP 2010-06-09 07:26:39

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Objective-c: Comparing two strings not working correctly.

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