determining UIFont's pointSize for a specific CGSize - ios

Question

I have a specific CGSize of a UILabel, where I cannot expand the frame of UILabel and since it is a multi-line UILabels adjustsFontSizeToFitWidth method does not work.
So I figured I should create such function which looked like;
- (CGFloat)fontSizeWithText:(NSString*)text andFont:(UIFont*)font constrainedSize:(CGSize)size LBM:(UILineBreakMode)LBM
{
// check if text fits to label
CGSize labelSize = [text sizeWithFont:font constrainedToSize:CGSizeMake(size.width, 9999) lineBreakMode:LBM];
// if not, decrease font size until it fits to the given size
while (labelSize.height > size.height) {
font = [UIFont fontWithName:font.fontName size:font.pointSize - 0.5];
labelSize = [text sizeWithFont:font constrainedToSize:CGSizeMake(size.width, 9999) lineBreakMode:LBM];
}
return font.pointSize;
}
Usage:
// fit detail label by arranging font's size
CGFloat fontSize = [self fontSizeWithText:self.titleLabel.text andFont:self.titleLabel.font constrainedSize:self.titleLabel.frame.size LBM:self.titleLabel.lineBreakMode];
self.titleLabel.font = [UIFont fontWithName:self.titleLabel.font.fontName size:fontSize];
But with this method, I see that some of my texts doesn't fit to the UILabel s frame and gets truncated. There must be something I am missing. Any help for the code or any other suggestions on resolving "fitting a text with given font to a specific multi-line UILabel" would be great.

Answer 1

First lets quickly take a look at the problem as a whole. You're trying to fit text into a predefined frame and adjust the font size. This generally will not work terribly well, as you will quickly hit sizes FAR too small to read, even on a retina display. You should adjust the frame of your label to accommodate the excess text (where possible. Sometimes, truncation is the only option.)
Now that, that is out of the way, lets take a look at adjusting the font size. Despite not recommending it, I will still explain how best to go about it.
Important, this code is untested, and will more than likely require some tweaks, but that can be an exercise of the reader.
So the first thing we need to know is the height of a single line. Now, we have the height of the label, and the number of lines it can display, so we can determine this by simply dividing the label height by the number of lines.
CGFloat optimalLineHeight = CGRectGetHeight(label.frame) / label.numberOfLines;
You may have noticed that this may return lines taller than are actually needed. You will be able to implement additional checks and constraints to deal with this. At current though, the font size will also be able to grow, and not just shrink.
Now, getting the optimal line height is just part of the story. We now need to optimise the font size. Here's some code:
CGFloat optimumFontSize = 0.0;
BOOL optimumFontSizeFound = NO;
do {
CGSize charSize = [#"M" sizeWithFont:[UIFont systemFontOfSize:optimumFontSize]
constrainedToSize:CGSizeMake(100, 9999)
lineBreakMode:0];
if ( CGSizeGetHeight(charSize) > optimalLineHeight ) {
optimumFontSizeFound = YES;
}
else {
optimumFontSize++;
}
} while ( !optimumFontSizeFound );
So what does this do? In this we keep track of the optimumFontSize so far. We start with the assumption of a font size of 0, and we see how tall a single character using that font size is. If that height is greater than the optimal line height previously calculated, then the previous height is the optimal one. If not, we increase the size and repeat until we do find the optimal one.
There are still a lot of issues to overcome in this to make it work perfectly in all situations. This should ensure that you don't get visible vertical clipping of characters, but it can't ensure that all the text content will display in the frame. To do that you'll need to be more intelligent in how you determine the number of lines required, but again I'll leave that as an exercise of the reader.
Hope this helps you towards your goal.