NSString font size specific to frame width

Question 1

OK never mind. Here's modified version of the same method that takes NSString for which to return a font:

    -(UIFont*)getFontForString:(NSString*)string
               toFitInRect:(CGRect)rect
                  seedFont:(UIFont*)seedFont{
    UIFont* returnFont = seedFont;
    CGSize stringSize = [string sizeWithAttributes:@{NSFontAttributeName : seedFont}];

    while(stringSize.width > rect.size.width){
        returnFont = [UIFont systemFontOfSize:returnFont.pointSize -1];
        stringSize = [string sizeWithAttributes:@{NSFontAttributeName : returnFont}];
    }

    return returnFont;
}

Here's how to call it:

NSString* stringToDraw = @"Test 123";

    CGRect rect = CGRectMake(100., 100., 100., 200.);
    UIFont* font = [self getFontForString:stringToDraw toFitInRect:rect seedFont:[UIFont systemFontOfSize:20]];
    [stringToDraw drawInRect:rect withFont:font];

Code is for iOS7+

Question 2

Trying font sizes with step 1.0 may be very slow. You can tremendously improve the algorithm by making two measures for two different sizes, then using linear approximation to guess the size that will be very close to the right one.

If it turns out not close enough, repeat the calculation using the guessed size instead of one of the previous two until it is good enough or stops changing:

// any values will do, prefer those near expected min and max
CGFloat size1 = 12.0, size2 = 56.0; 
CGFloat width1 = measure_for_size(size1);
CGFloat width2 = measure_for_size(size2);

while (1) {
    CGFloat guessed_size = size1 + (required_width - width1) * (size2 - size1) / (width2 - width1);

    width2 = measure_for_size(guessed_size);
    if ( fabs(guessed_size-size2) < some_epsilon || !is_close_enough(width2, required_width) ) {
        size2 = guessed_size;
        continue;
    }
    // round down to integer and clamp guessed_size as appropriate for your design
    return floor(clamp(guessed_size, 6.0, 24.0));
}

is_close_enough() implementation is completely up to you. Given that text width grows almost linearly of font size, you can simply drop it and just do 2-4 iterations which should be enough.

Question 3

I wanted to try to make a version that didn't have to repeatedly check font sizes using a do...while loop. Instead, I assumed that font point sizes were a linear scale, then worked out the size difference between the required frame width and the actual frame width, then adjusted the font size accordingly. Therefore, I ended up with this function:

+ (CGFloat)fontSizeToFitString:(NSString *)string inWidth:(float)width withFont:(UIFont *)font
{
    UILabel *label = [UILabel new];
    label.font = font;
    label.text = string;
    [label sizeToFit];

    float ratio = width / label.frame.size.width;
    return font.pointSize * ratio;
}

Pass in a font of any size, as well as the string and the required width, and it will return you the point size for that font.

I also wanted to take it a bit further and find out the font size for a multi-line string, so that the longest line would fit without a line break:

+ (CGFloat)fontSizeToFitLongestLineOfString:(NSString *)string inWidth:(float)width withFont:(UIFont *)font
{
    NSArray *stringLines = [string componentsSeparatedByString:@"\n"];

    UILabel *label = [UILabel new];
    label.font = font;

    float maxWidth = 0;

    for(NSString *line in stringLines)
    {
        label.text = line;
        [label sizeToFit];
        maxWidth = MAX(maxWidth, label.frame.size.width);
    }

    float ratio = width / maxWidth;
    return font.pointSize * ratio;
}

Seems to work perfectly fine for me. Hope it helps someone else.

Question 4

Original poster didn't specify what platform he was working on, but for OSX developers on Mavericks, sizeWithFont: doesn't exist and one should use sizeWithAttributes :

NSSize newSize = [aString sizeWithAttributes:
[NSDictionary dictionaryWithObjectsAndKeys:
           [NSFont fontWithName:@"Arial Rounded MT Bold" size:53.0],NSFontAttributeName,nil
]];

Question 5

Here's a method which can return you font that will fit in a rect:

-(UIFont*)getFontToFitInRect:(CGRect)rect seedFont:(UIFont*)seedFont{
    UIFont* returnFont = seedFont;
    CGSize stringSize = [self sizeWithFont:returnFont];

    while(stringSize.width > rect.size.width){
        returnFont = [UIFont systemFontOfSize:returnFont.pointSize -1];
        stringSize = [self sizeWithFont:returnFont];
    }

    return returnFont;
}

You can add this method to a NSString category. You can find more about how to add a category here: http://developer.apple.com/library/ios/#documentation/Cocoa/Conceptual/ProgrammingWithObjectiveC/CustomizingExistingClasses/CustomizingExistingClasses.html#//apple_ref/doc/uid/TP40011210-CH6-SW2

If you don't want to create a category, you can add this method to one of your utility classes and pass in the string for which you want the font to be returned.

Question 6

Here is another method, inspired by @puru020 & @jowie answers. Hope it helps someone

-(UIFont *) adjustedFontSizeForString:(NSString *)string forWidth:(float)originalWidth forFont:(UIFont *)font
{
    CGSize stringSize = [string sizeWithFont:font];
    if(stringSize.width <= originalWidth)
    {
        return font;
    }
    float ratio = originalWidth / stringSize.width;
    float fontSize = font.pointSize * ratio;
    return [font fontWithSize:fontSize];
}

Question 7

I modified a bit the solution of @puru020 , added the support for attributes, and improved a bit:

Note: The method should be wrapped in a NSString Category

- (UIFont*)requiredFontToFitInSize:(CGSize)size seedFont:(UIFont*)seedFont attributes:(NSDictionary*)attributes{
   UIFont *returnFont = [UIFont systemFontOfSize:seedFont.pointSize +1];
   NSMutableDictionary *mutableAttributes = attributes.mutableCopy;
   CGSize stringSize;

   do {
    returnFont = [UIFont systemFontOfSize:returnFont.pointSize -1];
    [mutableAttributes setObject:returnFont forKey:NSFontAttributeName];
    stringSize = [self sizeWithAttributes:mutableAttributes];
   } while (stringSize.width > size.width);

   return returnFont;
}