Finding the words

Recently I was challenged to build some code that could brake up an NSString into an array of NSStrings that would fit into a given width in an iOS app. Seems fairly straight forward, given that Apple has it in their text GUI elements. No dice my friends. While Apple does give you the ability to discover the dimensions of an NSString given a UIFont and, optionally, some size constraints it wont tell you how to break up the NSString into the individual lines.

So, what is one to do? Time to replicate some existing Apple capability. The basic idea is to split up a string into words, then build a line by adding a word at a time until it’s too long, then repeat until you’ve run out of tokens.

Splitting a string into words isn’t easy. My first stop was to use ParseKit. It’s a nice fast parser for Objective-C but it seems to have lost its support and hasn’t been updated in some time. The fact that it hasn’t been updated in a while made it a bit harder to integrate into the project. After a bit of pushing and pulling I managed to stuff it into the project.

Over all the ParseKit worked well enough and its compiled library wasn’t particularly big but it was a pain to install and has quiet a few warnings. I ended up fixing a bit of code and also adding a bunch of warning suppression so that I could work in peace.

I got the code to work but I wasn’t happy with all the extra code that was hanging around to make ParseKit work. So it was back to the drawing board. I dug around the net but didn’t find anything that I was happy with, time to reinvent the wheel.

What I ended up doing was making use of Objective-C regular expression engine, NSRegularExpression, and hand built a regular expression.

    NSMutableString *regexPattern = [NSMutableString string];
    // A number or dollar amount
    [regexPattern appendString:@"(\\$?\\d+(\\.\\d+)?)"];
    // or
    [regexPattern appendString:@"|"];
    // possibly starting with a quote, a word, possibly trailing by punctuation
    [regexPattern appendString:@"\\\"?([\\w\\']*)(\\.\\.\\.|\\.|,|-|!|\\?|:|;|\\\")?"];
    NSError *error = NULL;
    NSRegularExpression *regex = [NSRegularExpression regularExpressionWithPattern:regexPattern options:NSRegularExpressionCaseInsensitive error:&error];

Lines 3,5, and 7 or the different parts of the regular expression I built to parse words. Line 3 matches numbers as well as dollar values. line 5 is a simple ‘or’, and line 7 matches a word, consuming the leading quote if there is one, consuming trailing punctuation if that exists.┬áThe rest of the code in that method simply builds an array of all the tokens.

Here is the full code for turning a string into an array of words:

- (NSArray *)stringToWords{
    NSMutableString *regexPattern = [NSMutableString string];
    // A number or dollar amount
    [regexPattern appendString:@"(\\$?\\d+(\\.\\d+)?)"];
    // or
    [regexPattern appendString:@"|"];
    // possibly starting with a quote, a word, possibly trailing by punctuation
    [regexPattern appendString:@"\\\"?([\\w\\']*)(\\.\\.\\.|\\.|,|-|!|\\?|:|;|\\\")?"];
    NSError *error = NULL;
    NSRegularExpression *regex = [NSRegularExpression regularExpressionWithPattern:regexPattern options:NSRegularExpressionCaseInsensitive error:&error];

    NSArray *matches = [regex matchesInString:self
                                      options:0
                                        range:NSMakeRange(0, [self length])];
    NSMutableArray *tokens = [NSMutableArray array];
    NSUInteger endOfLastToken = 0;
    for (NSTextCheckingResult *match in matches) {
        NSRange matchRange = [match range];
        if (matchRange.location != endOfLastToken){
            NSRange tempRange = NSMakeRange(endOfLastToken, matchRange.location - endOfLastToken);
            [tokens addObject:[self substringWithRange:tempRange]];
        }
        [tokens addObject:[self substringWithRange:matchRange]];
        endOfLastToken = matchRange.location + matchRange.length;
    }

    return tokens;
}

And here is the full code for using that array of tokens to an array of lines:

- (NSArray *)linesConstrainedToWidth:(CGFloat)maxWidth withFirstLineIndent:(CGFloat)indent andFont:(UIFont *)font{
    CGSize maxSize = CGSizeMake(maxWidth - indent, FLT_MAX);

    NSMutableArray *strings = [NSMutableArray array];
    NSMutableString *newString = [NSMutableString string];
    NSMutableString *oldString = [NSMutableString string];

    NSArray *tokens = [self stringToWords];
    for (NSString *token in tokens){
        //NSLog(@"(%@) (%.1f) : %@", token.stringValue, token.floatValue, [token debugDescription]);
        [newString appendString:token];
        CGSize size = [newString sizeWithFont:font constrainedToSize:maxSize lineBreakMode:UILineBreakModeWordWrap];
        if (size.height > font.lineHeight){
            [strings addObject:oldString];
            newString = [NSMutableString stringWithString:token];
            maxSize = CGSizeMake(maxWidth, 2000.0);
        } else {
            oldString = [NSMutableString stringWithString:newString];
        }
    }
    [strings addObject:newString];

    return strings;
}

As you can see this method allows you to constrain the line to a specific width as well as setting a first line indent, just in case.

Warning be gone

In a previous post I talked about getting clang to be quite, ie every once in a blue moon you want a warning to simply go away. As I said, I’m really not a big fan of doing this, a warning usually means that something is wrong and you should fix it and not just ignore it.

For that once in a blue moon event I’ve got more detail on how to turn the warning suppression from a blunt instrument to a nice precision surgical instrument.

Inserting the following line in your code will suppress ARC performSelector warnings.

#pragma clang diagnostic ignored "-Warc-performSelector-leaks"

If you add a little more code

#pragma clang diagnostics push
#pragma clang diagnostic ignored "-Warc-performSelector-leaks"
// code  that needs a warning suppressed
#pragma clang diagnostics pop

You limit the impact of the suppression to just the bounds of the push and pop.

Of course the next part of the magic act is to figure out what exactly is the warning you want to suppress. Xcode does a fantastic job of giving you the human readable version. It actually gives you a running start before you slam into the brick wall. The problem is that there doesn’t appear to be a very good/complete list of human redable warnings and their official flag counterparts. So, what is one to do now?

Turn out that if you’re willing to peal away a layer of Xcode you can find the actual warning flag. Start by compiling your code, which will bring up the warning. Next, press Apple-7. This will bring up the Log Navigator. Click on the top log and scroll down until you find your warning. Click the detail button, its the rounded button with a set of horizontal lines. Now you see behind the Xcode curtain and see the gory detail. The top part of the details is the exact command used to compile your problem file. The bottom part gives you the details of the warning. If you examine the warning you’ll see that the ling ends with a [-Wwarning]. That’s it. This is the flag you want.

This is where I found info about the warning suppression push and pop ‘Disabling Clang Compiler Warnings’