UILabel *itemTitle = [[UILabel alloc] initWithFrame:CGRectMake(10.0f, 10,100, 200.0f)];
itemTitle.text = @"aseruy56uiytitfesh";
itemTitle.adjustsFontSizeToFitWidth = NO;
itemTitle.autoresizingMask = UIViewAutoresizingFlexibleWidth;
itemTitle.font = [UIFont boldSystemFontOfSize:18.0];
itemTitle.textColor = [UIColor blackColor];
itemTitle.shadowColor = [UIColor whiteColor];
itemTitle.shadowOffset = CGSizeMake(0, 1);
itemTitle.backgroundColor = [UIColor blueColor];
itemTitle.lineBreakMode = UILineBreakModeWordWrap;
itemTitle.numberOfLines = 0;
[itemTitle sizeToFit];
[self.view addSubview:itemTitle];

使用这里所有的属性都使用在标签上，并通过增加itemTitle中的文本来测试它。文本

itemTitle.text = @"diofgorigjveghnhkvjteinughntivugenvitugnvkejrfgnvkhv";

它会根据你的需要给出完美的答案

要在Swift3中做到这一点，以下是代码:

 let labelSizeWithFixedWith = CGSize(width: 300, height: CGFloat.greatestFiniteMagnitude)
            let exactLabelsize = self.label.sizeThatFits(labelSizeWithFixedWith)
            self.label.frame = CGRect(origin: CGPoint(x: 20, y: 20), size: exactLabelsize)

此方法适用于iOS 6和7

- (float)heightForLabelSize:(CGSize)maximumLabelSize  Font:(UIFont *)font String:(NSString*)string {

if ([[[UIDevice currentDevice] systemVersion] floatValue] >= 7) {
    NSDictionary *stringAttributes = [NSDictionary dictionaryWithObject:font forKey: NSFontAttributeName];

    CGSize adjustedLabelSize = [string maximumLabelSize
                                                                  options:NSStringDrawingTruncatesLastVisibleLine|NSStringDrawingUsesLineFragmentOrigin
                                                               attributes:stringAttributes context:nil].size;
    return adjustedLabelSize.height;
}
else {
    CGSize adjustedLabelSize = [string sizeWithFont:font constrainedToSize:maximumLabelSize lineBreakMode:NSLineBreakByWordWrapping];

    return adjustedLabelSize.height;
}

}

UILabel *itemTitle = [[UILabel alloc] initWithFrame:CGRectMake(10.0f, 10,100, 200.0f)];
itemTitle.text = @"aseruy56uiytitfesh";
itemTitle.adjustsFontSizeToFitWidth = NO;
itemTitle.autoresizingMask = UIViewAutoresizingFlexibleWidth;
itemTitle.font = [UIFont boldSystemFontOfSize:18.0];
itemTitle.textColor = [UIColor blackColor];
itemTitle.shadowColor = [UIColor whiteColor];
itemTitle.shadowOffset = CGSizeMake(0, 1);
itemTitle.backgroundColor = [UIColor blueColor];
itemTitle.lineBreakMode = UILineBreakModeWordWrap;
itemTitle.numberOfLines = 0;
[itemTitle sizeToFit];
[self.view addSubview:itemTitle];

使用这里所有的属性都使用在标签上，并通过增加itemTitle中的文本来测试它。文本

itemTitle.text = @"diofgorigjveghnhkvjteinughntivugenvitugnvkejrfgnvkhv";

它会根据你的需要给出完美的答案

对我来说，最简单和更好的方法是将高度约束应用于标签，并将优先级设置为低，即storyboard中的(250)。

所以你不需要担心通过编程计算高度和宽度，多亏了storyboard。

对于那些迁移到iOS 8的人，这里有一个Swift的类扩展:

extension UILabel {

    func autoresize() {
        if let textNSString: NSString = self.text {
            let rect = textNSString.boundingRectWithSize(CGSizeMake(self.frame.size.width, CGFloat.max),
                options: NSStringDrawingOptions.UsesLineFragmentOrigin,
                attributes: [NSFontAttributeName: self.font],
                context: nil)
            self.frame = CGRectMake(self.frame.origin.x, self.frame.origin.y, self.frame.size.width, rect.height)
        }
    }

}