How to figure out the font size of a UILabel when -adjustsFontSizeToFitWidth is set to YES?

When myLabel.adjustsFontSizeToFitWidth = YES, UILabel will adjust the font size automatically in case the text is too long for the label. For example, if my label is just 100px wide, and my text is too long to fit with the current font size, it will shrink down the font size until the text fits into the label.

I need to get the actual displayed font size from UILabel when 开发者_JAVA技巧the font size got shrunk down. For example, let's say my font size was actually 20, but UILabel had to shrink it down to 10. When I ask UILabel for the font and the font size, I get my old font size (20), but not the one that's displayed (10).

I'm not sure if this is entirely accurate, but it should be pretty close, hopefully. It may not take truncated strings into account, or the height of the label, but that's something you might be able to do manually.

The method

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

will return the text size, and notice that it also has a reference parameter for the actual font size used.

In case anybody still needs the answer. In iOS9 you can use boundingRectWithSize:options:context: to calculate actual font size. Note that context.minimumScaleFactor should not be 0.0 for scaling to work.

- (CGFloat)adjustedFontSizeForLabel:(UILabel *)label {
    NSMutableAttributedString *text = [[NSMutableAttributedString alloc] initWithAttributedString:label.attributedText];
    [text setAttributes:@{NSFontAttributeName:label.font} range:NSMakeRange(0, text.length)];

    NSStringDrawingContext *context = [NSStringDrawingContext new];
    context.minimumScaleFactor = label.minimumScaleFactor;
    [text boundingRectWithSize:label.frame.size options:NSStringDrawingUsesLineFragmentOrigin context:context];
    CGFloat adjustedFontSize = label.font.pointSize * context.actualScaleFactor;

    return adjustedFontSize;
}

For one-line UILabel works fine this simple solution:

//myLabel - initial label

UILabel *fullSizeLabel = [UILabel new];
fullSizeLabel.font = myLabel.font;
fullSizeLabel.text = myLabel.text;
[fullSizeLabel sizeToFit];

CGFloat actualFontSize = myLabel.font.pointSize * (myLabel.bounds.size.width / fullSizeLabel.bounds.size.width);

//correct, if new font size bigger than initial
actualFontSize = actualFontSize < myLabel.font.pointSize ? actualFontSize : myLabel.font.pointSize;

Swift 5

For one-line UILabel

extension UILabel {

    var actualFontSize: CGFloat {
    //initial label
     let fullSizeLabel = UILabel()
     fullSizeLabel.font = self.font
     fullSizeLabel.text = self.text
     fullSizeLabel.sizeToFit()

     var actualFontSize: CGFloat = self.font.pointSize * (self.bounds.size.width / fullSizeLabel.bounds.size.width);

    //correct, if new font size bigger than initial
     actualFontSize = actualFontSize < self.font.pointSize ? actualFontSize : self.font.pointSize;

     return actualFontSize
    }

}

Getting the actual font size is then as simple as:

let currentLabelFontSize = myLabel.actualFontSize

UILabel *txtLabel = [[UILabel alloc] initWithFrame:rectMax];
txtLabel.numberOfLines = 1;
txtLabel.font = self.fontMax;
txtLabel.adjustsFontSizeToFitWidth = YES;
txtLabel.minimumScaleFactor = 0.1;
[txtLabel setText:strMax];

UILabel *fullSizeLabel = [UILabel new];
fullSizeLabel.font = txtLabel.font;
fullSizeLabel.text = txtLabel.text;
fullSizeLabel.numberOfLines = 1;
[fullSizeLabel sizeToFit];

CGFloat actualFontSize = txtLabel.font.pointSize * (txtLabel.bounds.size.width / fullSizeLabel.bounds.size.width);
actualFontSize = actualFontSize < txtLabel.font.pointSize ? actualFontSize : txtLabel.font.pointSize;
// the actual font
self.fontMax = [UIFont fontWithName:self.fontMax.fontName size:actualFontSize];

my code works great, part from @Igor