iOS7之前和iOS7上面的解决方案

//
//  UILabel+DynamicHeight.m
//  For StackOverFlow
//
//  Created by Vijay on 24/02/14.
//  Copyright (c) 2014 http://Vijay-Apple-Dev.blogspot.com. All rights reserved.
//

#import <UIKit/UIKit.h>

#define SYSTEM_VERSION_GREATER_THAN_OR_EQUAL_TO(v)  ([[[UIDevice currentDevice] systemVersion] compare:v options:NSNumericSearch] != NSOrderedAscending)

#define SYSTEM_VERSION_LESS_THAN(v)                 ([[[UIDevice currentDevice] systemVersion] compare:v options:NSNumericSearch] == NSOrderedAscending)

#define iOS7_0 @"7.0"

@interface UILabel (DynamicHeight)

/*====================================================================*/

/* Calculate the size,bounds,frame of the Multi line Label */

/*====================================================================*/
/**
 *  Returns the size of the Label
 *
 *  @param aLabel To be used to calculte the height
 *
 *  @return size of the Label
 */

-(CGSize)sizeOfMultiLineLabel;

@end


//
//  UILabel+DynamicHeight.m
//  For StackOverFlow
//
//  Created by Vijay on 24/02/14.
//  Copyright (c) 2014 http://Vijay-Apple-Dev.blogspot.com. All rights reserved.
//

#import "UILabel+DynamicHeight.h"

@implementation UILabel (DynamicHeight)
/*====================================================================*/

/* Calculate the size,bounds,frame of the Multi line Label */

/*====================================================================*/
/**
 *  Returns the size of the Label
 *
 *  @param aLabel To be used to calculte the height
 *
 *  @return size of the Label
 */
-(CGSize)sizeOfMultiLineLabel{

    NSAssert(self, @"UILabel was nil");

    //Label text
    NSString *aLabelTextString = [self text];

    //Label font
    UIFont *aLabelFont = [self font];

    //Width of the Label
    CGFloat aLabelSizeWidth = self.frame.size.width;


    if (SYSTEM_VERSION_LESS_THAN(iOS7_0)) {
        //version < 7.0

        return [aLabelTextString sizeWithFont:aLabelFont
                            constrainedToSize:CGSizeMake(aLabelSizeWidth, MAXFLOAT)
                                lineBreakMode:NSLineBreakByWordWrapping];
    }
    else if (SYSTEM_VERSION_GREATER_THAN_OR_EQUAL_TO(iOS7_0)) {
        //version >= 7.0

        //Return the calculated size of the Label
        return [aLabelTextString boundingRectWithSize:CGSizeMake(aLabelSizeWidth, MAXFLOAT)
                                              options:NSStringDrawingUsesLineFragmentOrigin
                                           attributes:@{
                                                        NSFontAttributeName : aLabelFont
                                                        }
                                              context:nil].size;

    }

    return [self bounds].size;

}

@end

由于sizeWithFont已弃用，我使用这个代替。

这个得到标签特定属性。

-(CGFloat)heightForLabel:(UILabel *)label withText:(NSString *)text{

    NSAttributedString *attributedText = [[NSAttributedString alloc] initWithString:text attributes:@{NSFontAttributeName:label.font}];
    CGRect rect = [attributedText boundingRectWithSize:(CGSize){label.frame.size.width, CGFLOAT_MAX}
                                           options:NSStringDrawingUsesLineFragmentOrigin
                                           context:nil];

    return ceil(rect.size.height);
}

你也可以把它作为一种方法。@Pyjamasam是非常正确的，所以我只是在创建它的方法。它可能对其他人有帮助

-(CGRect)setDynamicHeightForLabel:(UILabel*)_lbl andMaxWidth:(float)_width{
    CGSize maximumLabelSize = CGSizeMake(_width, FLT_MAX);

    CGSize expectedLabelSize = [_lbl.text sizeWithFont:_lbl.font constrainedToSize:maximumLabelSize lineBreakMode:_lbl.lineBreakMode];

    //adjust the label the the new height.
    CGRect newFrame = _lbl.frame;
    newFrame.size.height = expectedLabelSize.height;
    return newFrame;
}

就像这样

label.frame = [self setDynamicHeightForLabel:label andMaxWidth:300.0];

NSString *str = @"Please enter your text......";
CGSize lblSize = [str sizeWithFont:[UIFont systemFontOfSize:15] constrainedToSize: CGSizeMake(200.0f, 600.0f) lineBreakMode: NSLineBreakByWordWrapping];

UILabel *label = [[UILabel alloc]init];
label.frame = CGRectMake(60, 20, 200, lblSize.height);
label.numberOfLines = 0;
label.lineBreakMode = NSLineBreakByWordWrapping;
label.font = [UIFont systemFontOfSize:15];
label.text = str;
label.backgroundColor = [UIColor clearColor];
[label sizeToFit];
[self.view addSubview:label];

你可以通过以下方式实现TableViewController的(UITableViewCell *)tableView:cellForRowAtIndexPath方法(例如):

#define CELL_LABEL_TAG 1

- (UITableViewCell *)tableView:(UITableView *)tableView  cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    NSString *text = @"my long text";

    static NSString *MyIdentifier = @"MyIdentifier";
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:MyIdentifier];
    if (cell == nil) {
        cell = [[[UITableViewCell alloc] initWithFrame:CGRectZero  reuseIdentifier:identifier] autorelease];
    }

    CGFloat width = [UIScreen mainScreen].bounds.size.width - 50;
    CGFloat height = [self textHeight:text] + 10;
    CGRect frame = CGRectMake(10.0f, 10.0f, width, height);

    UILabel *cellLabel = [[UILabel alloc] initWithFrame:frame];
    cellLabel.tag = CELL_LABEL_TAG;
    cellLabel.textColor = [UIColor blackColor];
    cellLabel.backgroundColor = [UIColor clearColor];
    cellLabel.textAlignment = UITextAlignmentLeft;
    cellLabel.font = [UIFont systemFontOfSize:12.0f];
    [cell.contentView addSubview:cellLabel];
    [cellLabel release];

    return cell;
}

UILabel *label = (UILabel *)[cell viewWithTag:CELL_LABEL_TAG];
label.text = text;
label.numberOfLines = 0;
[label sizeToFit];
return cell;

也可以使用NSString的sizeWithFont:constrainedToSize:lineBreakMode:方法来计算文本的高度。

基于Swift 4及以上答案的UILabel扩展

extension UILabel {

    func retrieveTextHeight () -> CGFloat {
        let attributedText = NSAttributedString(string: self.text!, attributes: [NSFontAttributeName:self.font])

        let rect = attributedText.boundingRect(with: CGSize(width: self.frame.size.width, height: CGFloat.greatestFiniteMagnitude), options: .usesLineFragmentOrigin, context: nil)

        return ceil(rect.size.height)
    }

}

可以这样使用:

self.labelHeightConstraint.constant = self.label.retrieveTextHeight()