How to adjust font size of label to fit the rectangle?

Question

Yeah, there\'s this cool myLabel.adjustsFontSizeToFitWidth = YES; property. But as soon as the label has two lines or more, it won\'t resize the text to anythin

Answer 1

I have created Category for UILabel based on @agarcian's answer. But i calculate fontSize depending on square needed on screen for drawing text. This method not need loops and calculating is done by one iteration.

Here the .h file:

//  UILabel+Extended.h
//  Created by Firuz on 16/08/14.
//  Copyright (c) 2014. All rights reserved.

#import <UIKit/UIKit.h>

@interface UILabel (Extended)

/** This method calculate the optimal font size for current number of lines in UILable. Mus be called after drawing UILabel view */
- (NSInteger)fontSizeWithMinFontSize:(NSInteger)minFontSize withMaxFontSize:(NSInteger)maxFontSize;

@end

And here the .m file:

//  UILabel+Extended.m
//  Created by Firuz on 16/08/14.
//  Copyright (c) 2014. All rights reserved.

#import "UILabel+Extended.h"

@implementation UILabel (Extended)

- (NSInteger)fontSizeWithMinFontSize:(NSInteger)minFontSize withMaxFontSize:(NSInteger)maxFontSize
{
    if (maxFontSize < minFontSize) {
        return 0;
    }

    UIFont *font = [UIFont fontWithName:self.font.fontName size:maxFontSize];

    CGFloat lineHeight = [font lineHeight];

    CGSize constraintSize = CGSizeMake(MAXFLOAT, lineHeight);

    CGRect rect = [self.text boundingRectWithSize:constraintSize
                                           options:NSStringDrawingUsesLineFragmentOrigin
                                        attributes:@{NSFontAttributeName : font}
                                           context:nil];

    CGFloat labelSqr = self.frame.size.width * self.frame.size.height;
    CGFloat stringSqr = rect.size.width/self.frame.size.width * (lineHeight + font.pointSize) * self.frame.size.width;

    CGFloat multiplyer = labelSqr/stringSqr;

    if (multiplyer < 1) {
        if (minFontSize < maxFontSize*multiplyer) {
            return maxFontSize * multiplyer;
        } else {
            return minFontSize;
        }
    }
    return maxFontSize;
}

@end

Answer 2

Swift 3 "binary search solution" based on this answer with minor improvements. Sample is in context of UITextView subclass:

func binarySearchOptimalFontSize(min: Int, max: Int) -> Int {
    let middleSize = (min + max) / 2

    if min > max {
        return middleSize
    }

    let middleFont = UIFont(name: font!.fontName, size: CGFloat(middleSize))!

    let attributes = [NSFontAttributeName : middleFont]
    let attributedString = NSAttributedString(string: text, attributes: attributes)

    let size = CGSize(width: bounds.width, height: .greatestFiniteMagnitude)
    let options: NSStringDrawingOptions = [.usesLineFragmentOrigin, .usesFontLeading]
    let textSize = attributedString.boundingRect(with: size, options: options, context: nil)

    if textSize.size.equalTo(bounds.size) {
        return middleSize
    } else if (textSize.height > bounds.size.height || textSize.width > bounds.size.width) {
        return binarySearchOptimalFontSize(min: min, max: middleSize - 1)
    } else {
        return binarySearchOptimalFontSize(min: middleSize + 1, max: max)
    }
}

I hope that helps someone.