Calculate Font Size to Fit Frame - Core Text - NSAttributedString - iOS

A little trick helps to make use of sizeWithAttributes: without the need of iterating for the right result:

NSSize sampleSize = [wordString sizeWithAttributes:
    @{ NSFontAttributeName: [NSFont fontWithName:fontName size:fontSize] }];
CGFloat ratio = rect.size.width / sampleSize.width;
fontSize *= ratio;

Make sure the fontSize for the sample is big enough to get good results.

The only way I can see this being possible is to have a system that runs the size calculation then adjusts the size and repeats until it finds the right size.

I.e. set up a bisecting algorithm that goes between certain sizes.

i.e. run it for size 10. Too small. Size 20. Too small. Size 30. Too big. Size 25. Too small. Size 27. Just right, use size 27.

You could even start in hundreds.

Size 100. Too big. Size 50. etc...

Here is a simple piece of code that will figure out the maximum font size to fit within the bounds of a frame:

UILabel *label = [[UILabel alloc] initWithFrame:frame];
label.text = @"Some text";
float largestFontSize = 12;
while ([label.text sizeWithAttributes:@{NSFontAttributeName:[UIFont systemFontOfSize:largestFontSize]}].width > modifierFrame.size.width)
{
     largestFontSize--;
}
label.font = [UIFont systemFontOfSize:largestFontSize];