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];

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

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];

最后，它成功了。谢谢大家。

我没有让它工作，因为我试图在heightForRowAtIndexPath方法中调整标签的大小:

- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath

和(是的，我很傻)，我在cellForRowAtIndexPath方法中调整标签的默认大小-我忽略了我之前写的代码:

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath

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

这是使用Objective-c获取UILabel Height的一行代码:

labelObj.numberOfLines = 0;
CGSize neededSize = [labelObj sizeThatFits:CGSizeMake(screenWidth, CGFLOAT_MAX)];

使用.height你会得到标签的高度，如下所示:

neededSize.height