iPhone UILabel sizeWithFont:

Question

I'm trying to measure the visual size of a NSString that takes into account the number of lines I can render. However, sizeWithFont doesn't take into account numberOfLines property? So my layout algorithm positions everything lower than they actually need to be.

_price = [[UILabel alloc] init];
_price.text = myPriceValue;
_price.lineBreakMode = UILineBreakModeWordWrap;
_price.numberOfLines = 3;
_price.backgroundColor = [UIColor clearColor];
_price.textColor = TTSTYLEVAR(colorPrice);
/// the follow code ignores numberOfLines and just tells me the size of the whole block.  
// I'd like it to be aware of numberOfLines
//
CGSize priceSize = [_price.text sizeWithFont:_price.font
        constrainedToSize:CGSizeMake(maxWidth, CGFLOAT_MAX)
        lineBreakMode:UILineBreakModeWordWrap];

Does anyone know how to do this using the iPhone SDK?

Answer 1

Instead of CGFLOAT_MAX for the max height of your text calculation, try getting the size of one line with this:

[_price.text sizeWithFont:_price.font].height

and then multiplying that by the maximum # of lines you want, then plugging that into the height of the size you are constraining yourself to. It'd probably look like this:

_price = [[UILabel alloc] init];
_price.text = myPriceValue;
_price.lineBreakMode = UILineBreakModeWordWrap;
_price.numberOfLines = 3;
_price.backgroundColor = [UIColor clearColor];
_price.textColor = TTSTYLEVAR(colorPrice);
CGFloat lineHeight = [_price.text sizeWithFont:_price.font].height;
CGSize priceSize = [_price.text sizeWithFont:_price.font
        constrainedToSize:CGSizeMake(maxWidth, lineHeight * _price.numberOfLines)
        lineBreakMode:UILineBreakModeWordWrap];

Don't use this if you ever set number of lines to 0 as your max height will be 0 in that case; you should use CGFLOAT_MAX then.

Answer 2

Use the UILabel's sizeToFit instead of sizeWithFont: to layout a multi-line UILabel, since sizeWithFont: will truncate the string (see apple docs). The following code reduces the font size of a label until the text fit into a the specified size... multiple lines of text will be used as soon as they fit into the specified height:

-(void)setFontSizeOfMultiLineLabel: (UILabel*)label 
        toFitSize: (CGSize) size 
        forMaxFontSize: (CGFloat) maxFontSize 
        andMinFontSize: (CGFloat) minFontSize 
        startCharacterWrapAtSize: (CGFloat)characterWrapSize{

CGRect constraintSize = CGRectMake(0, 0, size.width, 0);
label.frame = constraintSize;
label.lineBreakMode = UILineBreakModeWordWrap;
label.numberOfLines = 0; // allow any number of lines

for (int i = maxFontSize; i > minFontSize; i--) {

    if((i < characterWrapSize) && (label.lineBreakMode == UILineBreakModeWordWrap)){
        // start over again with lineBreakeMode set to character wrap 
        i = maxFontSize;
        label.lineBreakMode = UILineBreakModeCharacterWrap;
    }

    label.font = [label.font fontWithSize:i];
    [label sizeToFit];
    if(label.frame.size.height < size.height){
        break;
    }       
    label.frame = constraintSize;
  } 
}

Call this with a label that has your favorite text and font:

UILabel *label = [[UILabel alloc] initWithFrame: CGRectZero];   
label.backgroundColor = [UIColor clearColor];   
label.textColor = [UIColor whiteColor];
label.text = text;
label.font = [UIFont fontWithName: @"Helvetica" size: 16];
[self setFontSizeOfMultiLineLabel: label toFitSize: CGSizeMake(200, 44) forMaxFontSize: 16 andMinFontSize: 8 startCharacterWrapAtSize: 11]; 

The startCharacterWrapAtSize parameter lets you choose to use characterWrap starting at the giving font size. This should save space in the case wordWrap would use really small fonts.

edit: bugfix