Question

I have a UILabel in which the text is automatically shrunk to fit. Once this has happened, I need to know the point size of the resulting font so that I can set that exact same size in another label elsewhere.

If I access label.font.pointSize I get back the original size, not the shrunk size. So I then tried using this NSString addition to calculate the font size:

- (CGSize)sizeWithFont:(UIFont *)font minFontSize:(CGFloat)minFontSize actualFontSize:(CGFloat *)actualFontSize forWidth:(CGFloat)width lineBreakMode:(UILineBreakMode)lineBreakMode

However, that doesn’t work for me either because if doesn’t take into account the label’s height constraint, only its width. (In my case the font needs shrinking further to fit in the frame’s height).

This seems to leave me with just one absolutely horrible option, and that’s to call the following function repeatedly until I’ve found the maximum height that will actually fit into the frame:

- (CGSize)sizeWithFont:(UIFont *)font constrainedToSize:(CGSize)size lineBreakMode:(UILineBreakMode)lineBreakMode

Clearly that would be both very inefficient and nasty.

Does anyone have a better solution?

Tim

Answer 1

Well, in the advent that no-one can provide me with a better option, I thought I’d share a category that I’ve written to solve the problem the hard way.

However, if there’s a direct way to access the shrunk font size of a UILabel that’d obviously be ideal…

Without further ado, this function will return an auto-shrunk font size that fits within the constrained size.

Interface:

 @interface NSString (FontSize)

- (CGSize)sizeWithFont:(UIFont *)font
           minFontSize:(CGFloat)minFontSize
        actualFontSize:(CGFloat *)actualFontSize
     constrainedToSize:(CGSize)maxSize
         lineBreakMode:(UILineBreakMode)lineBreakMode;

@end

Implementation:

@implementation NSString (FontSize)

- (CGSize)sizeWithFont:(UIFont *)font
           minFontSize:(CGFloat)minFontSize
        actualFontSize:(CGFloat *)actualFontSize
     constrainedToSize:(CGSize)maxSize
         lineBreakMode:(UILineBreakMode)lineBreakMode
{
    CGFloat size;
    CGSize boundingBox;

    // First, get the OS to fit the text into the width

    boundingBox = [self sizeWithFont:font
                         minFontSize:minFontSize
                      actualFontSize:&size
                            forWidth:maxSize.width
                       lineBreakMode:lineBreakMode];

    // Return here if the min size has already been reached

    if (size <= minFontSize)
    {
        *actualFontSize = size;
        return boundingBox;
    }

    // Binary search biggest size that will fit within the height of the box    

    CGFloat upperBound = size;
    CGFloat lowerBound = minFontSize;

    UIFont *f;
    CGFloat fontSize;
    while (upperBound > lowerBound + 0.5) {

        fontSize = (upperBound + lowerBound) / 2;

        f = [UIFont fontWithName:font.fontName size:fontSize];
        boundingBox = [self sizeWithFont:f];

        if (boundingBox.height > maxSize.height)
            upperBound = fontSize - 0.5;
        else
            lowerBound = fontSize;
    }

    // Return the result

    *actualFontSize = fontSize;
    return boundingBox;
}

@end