单线——有两种方法，你可以简单地改变。

1- pragmatic (Swift 3)

只需添加以下代码

    yourLabel.numberOfLines = 1;
    yourLabel.minimumScaleFactor = 0.7;
    yourLabel.adjustsFontSizeToFitWidth = true;

2 -使用UILabel属性检查器

i- Select your label- Set number of lines 1.
ii- Autoshrink-  Select Minimum Font Scale from drop down
iii- Set Minimum Font Scale value as you wish , I have set 0.7 as in below image. (default is 0.5)

它有点不复杂，但这应该是可行的， 例如，假设你想把你的uilabel设置为120x120，最大字体大小为28:

magicLabel.numberOfLines = 0;
magicLabel.lineBreakMode = NSLineBreakByWordWrapping;
...
magicLabel.text = text;
    for (int i = 28; i>3; i--) {
        CGSize size = [text sizeWithFont:[UIFont systemFontOfSize:(CGFloat)i] constrainedToSize:CGSizeMake(120.0f, CGFLOAT_MAX) lineBreakMode:NSLineBreakByWordWrapping];
        if (size.height < 120) {
            magicLabel.font = [UIFont systemFontOfSize:(CGFloat)i];
            break;
        }
    }

下面是一个UILabel子类的填充代码，它实现了动画字体大小的改变:

@interface SNTextLayer : CATextLayer

@end

@implementation SNTextLayer

- (void)drawInContext:(CGContextRef)ctx {
    // We override this to make text appear at the same vertical positon as in UILabel
    // (otherwise it's shifted tdown)
    CGFloat height = self.bounds.size.height;
    float fontSize = self.fontSize;
    // May need to adjust this somewhat if it's not aligned perfectly in your implementation
    float yDiff = (height-fontSize)/2 - fontSize/10;

    CGContextSaveGState(ctx);
    CGContextTranslateCTM(ctx, 0.0, yDiff);
    [super drawInContext:ctx];
     CGContextRestoreGState(ctx);
}

@end

@interface SNAnimatableLabel ()

@property CATextLayer* textLayer;

@end

@interface SNAnimatableLabel : UILabel

- (void)animateFontToSize:(CGFloat)fontSize withDuration:(double)duration;

@end



@implementation SNAnimatableLabel


- (void)awakeFromNib {
    [super awakeFromNib];
    _textLayer = [SNTextLayer new];
    _textLayer.backgroundColor = self.backgroundColor.CGColor;
    _textLayer.foregroundColor = self.textColor.CGColor;
    _textLayer.font = CGFontCreateWithFontName((CFStringRef)self.font.fontName);
    _textLayer.frame = self.bounds;
    _textLayer.string = self.text;
    _textLayer.fontSize = self.font.pointSize;
    _textLayer.contentsScale = [UIScreen mainScreen].scale;
    [_textLayer setPosition: CGPointMake(CGRectGetMidX(_textLayer.frame), CGRectGetMidY(_textLayer.frame))];
    [_textLayer setAnchorPoint: CGPointMake(0.5, 0.5)];
    [_textLayer setAlignmentMode: kCAAlignmentCenter];
    self.textColor = self.backgroundColor;
    // Blend text with background, so that it doens't interfere with textlayer text
    [self.layer addSublayer:_textLayer];
    self.layer.masksToBounds = NO;
}

- (void)setText:(NSString *)text {
    _textLayer.string = text;
    super.text = text;
}

- (void)layoutSubviews {
    [super layoutSubviews];
    // Need to enlarge the frame, otherwise the text may get clipped for bigger font sizes
    _textLayer.frame = CGRectInset(self.bounds, -5, -5);
}

- (void)animateFontToSize:(CGFloat)fontSize withDuration:(double)duration {
    [CATransaction begin];
    [CATransaction setAnimationDuration:duration];
    _textLayer.fontSize = fontSize;
    [CATransaction commit];
}

一行:

factLabel.numberOfLines = 1;
factLabel.minimumFontSize = 8;
factLabel.adjustsFontSizeToFitWidth = YES;

上面的代码将调整你的文本的字体大小(例如)8试图适合你的文本在标签。 numberolines = 1是必选项。

多行:

对于numberolines > 1，有一个方法可以通过NSString的sizeWithFont来计算最终文本的大小:…UIKit添加方法，例如:

CGSize lLabelSize = [yourText sizeWithFont:factLabel.font
                                  forWidth:factLabel.frame.size.width
                             lineBreakMode:factLabel.lineBreakMode];

之后，你可以使用产生的lLabelSize来调整你的标签大小，例如(假设你只会改变标签的高度):

factLabel.frame = CGRectMake(factLabel.frame.origin.x, factLabel.frame.origin.y, factLabel.frame.size.width, lLabelSize.height);

iOS6

一行:

从iOS6开始，minimumFontSize已弃用。这条线

factLabel.minimumFontSize = 8.;

可更改为:

factLabel.minimumScaleFactor = 8./factLabel.font.pointSize;

iOS7

多行:

从iOS7开始，sizeWithFont不再使用。 多行大小写简化为:

factLabel.numberOfLines = 0;
factLabel.lineBreakMode = NSLineBreakByWordWrapping;
CGSize maximumLabelSize = CGSizeMake(factLabel.frame.size.width, CGFLOAT_MAX);
CGSize expectSize = [factLabel sizeThatFits:maximumLabelSize];
factLabel.frame = CGRectMake(factLabel.frame.origin.x, factLabel.frame.origin.y, expectSize.width, expectSize.height);

iOS 13 (Swift 5):

label.adjustsFontSizeToFitWidth = true
label.minimumScaleFactor = 0.5

斯威夫特版本:

textLabel.adjustsFontSizeToFitWidth = true
textLabel.minimumScaleFactor = 0.5

这是一个快速扩展UILabel。它运行一个二进制搜索算法，根据标签边界的宽度和高度调整字体大小。测试工作与iOS 9和自动布局。

用法:<label>是预定义的需要调整字体大小的UILabel

<label>.fitFontForSize()

默认情况下，该函数在5pt和300pt的字体大小范围内搜索，并将字体设置为“完全”适合其文本的范围(精确到1.0pt)。你可以定义参数，这样，例如，它在1pt和标签当前字体大小之间精确搜索0.1pts，如下所示:

<label>.fitFontForSize(1.0, maxFontSize: <label>.font.pointSize, accuracy:0.1)

复制/粘贴以下代码到您的文件中

extension UILabel {

    func fitFontForSize(var minFontSize : CGFloat = 5.0, var maxFontSize : CGFloat = 300.0, accuracy : CGFloat = 1.0) {
        assert(maxFontSize > minFontSize)
        layoutIfNeeded() // Can be removed at your own discretion
        let constrainedSize = bounds.size
        while maxFontSize - minFontSize > accuracy {
            let midFontSize : CGFloat = ((minFontSize + maxFontSize) / 2)
            font = font.fontWithSize(midFontSize)
            sizeToFit()
            let checkSize : CGSize = bounds.size
            if  checkSize.height < constrainedSize.height && checkSize.width < constrainedSize.width {
                minFontSize = midFontSize
            } else {
                maxFontSize = midFontSize
            }
        }
        font = font.fontWithSize(minFontSize)
        sizeToFit()
        layoutIfNeeded() // Can be removed at your own discretion
    }

}

注意:每个layoutIfNeeded()调用都可以自行删除