-(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    cellIdentifier = @"myCell";
    cell = [tableView dequeueReusableCellWithIdentifier:cellIdentifier];
    cell.myUILabel.lineBreakMode = UILineBreakModeWordWrap;        
    cell.myUILabel.numberOfLines = 0;
    cell.myUILabel.text = @"Some very very very very long text....."
    [cell.myUILabel.criterionDescriptionLabel sizeToFit];    
}

- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath
{
    UITableViewCell *cell = [self tableView:tableView cellForRowAtIndexPath:indexPath];
    CGFloat rowHeight = cell.myUILabel.frame.size.height + 10;

    return rowHeight;    
}

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];

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;
}

}

我的代码:

UILabel *label      = [[UILabel alloc] init];
label.numberOfLines = 0;
label.lineBreakMode = NSLineBreakByWordWrapping;
label.text          = text;
label.textAlignment = NSTextAlignmentCenter;
label.font          = [UIFont fontWithName:_bodyTextFontFamily size:_bodyFontSize];

CGSize size = [label sizeThatFits:CGSizeMake(width, MAXFLOAT)];


float height        = size.height;
label.frame         = CGRectMake(x, y, width, height);

sizeWithFont constrainedToSize:lineBreakMode:是使用的方法。如何使用它的例子如下:

//Calculate the expected size based on the font and linebreak mode of your label
// FLT_MAX here simply means no constraint in height
CGSize maximumLabelSize = CGSizeMake(296, FLT_MAX);

CGSize expectedLabelSize = [yourString sizeWithFont:yourLabel.font constrainedToSize:maximumLabelSize lineBreakMode:yourLabel.lineBreakMode];   

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

这种方法可以得到完美的高度

-(float) getHeightForText:(NSString*) text withFont:(UIFont*) font andWidth:(float) width{
CGSize constraint = CGSizeMake(width , 20000.0f);
CGSize title_size;
float totalHeight;


title_size = [text boundingRectWithSize:constraint
                                options:NSStringDrawingUsesLineFragmentOrigin
                             attributes:@{ NSFontAttributeName : font }
                                context:nil].size;

totalHeight = ceil(title_size.height);

CGFloat height = MAX(totalHeight, 40.0f);
return height;
}