有两种方法可以解决这个问题。一种是

[mylabel setNumberOfLines:0];
[mylabel sizeToFit];

但是第二种方法对于这种方法更可靠，

 CGSize sizeToFit = [label.text sizeWithFont:label.font constrainedToSize:maxSize lineBreakMode:label.lineBreakMode];
 [mylabel setFrame:CGRectMake(mylabel.frame.origin.x, mylabel.frame.origin.y, sizeToFit.width, sizeToFit.height)];

输入“\n”不是一件好事，但如果您知道将要显示的数据的约束和大小，则可以，如果文本长度大于标签的大小，则可能会很好，但无法扩展。第二种方式最终根据要显示的文本的大小设置框架。

如果可以选择创建自己的自定义视图，可以执行以下操作：

- (void)drawRect:(CGRect)rect
{
    CGRect bounds = self.bounds;
    [self.textColor set];
    [self.text drawInRect:bounds
                 withFont:self.font
            lineBreakMode:UILineBreakModeTailTruncation
                alignment:self.textAlignment];
}

Swift 4.0中有一个解决方案：

func viewDidLoad() {

    super.viewDidLoad()

    // 20 point top and left margin. Sized to leave 20 pt at right.
    let labelFrame = CGRect(x: 20, y: 20, width: 280, height: 150)
    let myLabel = UILabel(frame: labelFrame)
    myLabel.backgroundColor = UIColor.orange

    let labelText = "I am the very model of a modern Major-General, 
    I've information vegetable, animal, and mineral"
    myLabel.text = labelText

    // Tell the label to use an unlimited number of lines
    myLabel.numberOfLines = 0
    myLabel.sizeToFit()

    view.addSubview(myLabel) // add label
}

使用textRect（对于边界：limitedToNumberOfLines:）。

class TopAlignedLabel: UILabel {
  override func drawText(in rect: CGRect) {
    let textRect = super.textRect(forBounds: bounds, limitedToNumberOfLines: numberOfLines)
    super.drawText(in: textRect)
  }
}

Swift 2.0版本：

在空Swift文件中生成常量枚举值。

//  AppRef.swift

import UIKit
import Foundation

enum UILabelTextPositions : String {

 case VERTICAL_ALIGNMENT_TOP = "VerticalAlignmentTop"
 case VERTICAL_ALIGNMENT_MIDDLE = "VerticalAlignmentMiddle"
 case VERTICAL_ALIGNMENT_BOTTOM = "VerticalAlignmentBottom"

}

使用UILabel扩展：

创建一个空的Swift类并命名它

//  AppExtensions.swift

import Foundation
import UIKit

extension UILabel{ 
 func makeLabelTextPosition (sampleLabel :UILabel?, positionIdentifier : String) -> UILabel
 {
  let rect = sampleLabel!.textRectForBounds(bounds, limitedToNumberOfLines: 0)

  switch positionIdentifier
  {
  case "VerticalAlignmentTop":
   sampleLabel!.frame = CGRectMake(bounds.origin.x+5, bounds.origin.y, rect.size.width, rect.size.height)
   break;

  case "VerticalAlignmentMiddle":
   sampleLabel!.frame = CGRectMake(bounds.origin.x+5,bounds.origin.y + (bounds.size.height - rect.size.height) / 2,
    rect.size.width, rect.size.height);
   break;

  case "VerticalAlignmentBottom":
   sampleLabel!.frame = CGRectMake(bounds.origin.x+5, bounds.origin.y + (bounds.size.height - rect.size.height),rect.size.width, rect.size.height);
   break;

  default:
   sampleLabel!.frame = bounds;
   break;
  }
  return sampleLabel!

 }
}

用法：

myMessageLabel.makeLabelTextPosition(messageLabel, positionIdentifier: UILabelTextPositions.VERTICAL_ALIGNMENT_TOP.rawValue)

创建UILabel的子类。就像一个魅力：

// TopLeftLabel.h

#import <Foundation/Foundation.h>

@interface TopLeftLabel : UILabel 
{
}

@end

// TopLeftLabel.m

#import "TopLeftLabel.h"

@implementation TopLeftLabel

- (id)initWithFrame:(CGRect)frame 
{
    return [super initWithFrame:frame];
}

- (CGRect)textRectForBounds:(CGRect)bounds limitedToNumberOfLines:(NSInteger)numberOfLines 
{
    CGRect textRect = [super textRectForBounds:bounds limitedToNumberOfLines:numberOfLines];    
    textRect.origin.y = bounds.origin.y;
    return textRect;
}

-(void)drawTextInRect:(CGRect)requestedRect 
{
    CGRect actualRect = [self textRectForBounds:requestedRect limitedToNumberOfLines:self.numberOfLines];
    [super drawTextInRect:actualRect];
}

@end

正如这里所讨论的。