你的方向是对的。你所需要做的就是:

myUILabel.numberOfLines = 0;
myUILabel.text = @"Enter large amount of text here";
[myUILabel sizeToFit];

根据iOS7更新

// If description are available for protocol
protocolDescriptionLabel.text = [dataDictionary objectForKey:@"description"];
[protocolDescriptionLabel sizeToFit];
[protocolDescriptionLabel setLineBreakMode:NSLineBreakByWordWrapping];

CGSize expectedLabelSize = [protocolDescriptionLabel
               textRectForBounds:protocolDescriptionLabel.frame
               limitedToNumberOfLines:protocolDescriptionLabel.numberOfLines].size;
NSLog(@"expectedLabelSize %f", expectedLabelSize.height);

//adjust the label the the new height.
CGRect newFrame = protocolDescriptionLabel.frame;
newFrame.size.height = expectedLabelSize.height;
protocolDescriptionLabel.frame = newFrame;

你的方向是对的。你所需要做的就是:

myUILabel.numberOfLines = 0;
myUILabel.text = @"Enter large amount of text here";
[myUILabel sizeToFit];

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。

斯威夫特2:

    yourLabel.text = "your very long text"
    yourLabel.numberOfLines = 0
    yourLabel.lineBreakMode = NSLineBreakMode.ByWordWrapping
    yourLabel.frame.size.width = 200
    yourLabel.frame.size.height = CGFloat(MAXFLOAT)
    yourLabel.sizeToFit()

有趣的是sizeToFit()将frame.size.height设置为最大浮动，这将为长文本提供空间，但sizeToFit()将强制它只使用必要的，但总是在设置.frame.size.height后调用它。

我建议为调试目的设置. backgroundcolor，这样你就可以看到为每个情况呈现的帧。

以下是分类版本:

UILabel + AutoSize.h #进口

@interface UILabel (AutoSize)

- (void) autosizeForWidth: (int) width;

@end

UILabel + AutoSize。m

#import "UILabel+AutoSize.h"

@implementation UILabel (AutoSize)

- (void) autosizeForWidth: (int) width {
    self.lineBreakMode = UILineBreakModeWordWrap;
    self.numberOfLines = 0;
    CGSize maximumLabelSize = CGSizeMake(width, FLT_MAX);
    CGSize expectedLabelSize = [self.text sizeWithFont:self.font constrainedToSize:maximumLabelSize lineBreakMode:self.lineBreakMode];
    CGRect newFrame = self.frame;
    newFrame.size.height = expectedLabelSize.height;
    self.frame = newFrame;
}

@end