I want to take a standard UILabel and increase the font size so that it fills the vertical space. Taking inspiration from the accepted answer for this question, I defined a subclass on UILabel with this drawRect implementation:
- (void)drawRect:(CGRect)rect
{
// Size required to render string
CGSize size = [self.text sizeWithFont:self.font];
// For current font point size, calculate points per pixel
float pointsPerPixel = size.height / self.font.pointSize;
// Scale up point size for the height of the label
float desiredPointSize = rect.size.height * pointsPerPixel;
// Create and assign new UIFont with desired point Size
UIFont *newFont = [UIFont fontWithName:self.font.fontName size:desiredPointSize];
self.font = newFont;
// Call super
[super drawRect:rect];
}
But this doesn't work as it scales the font beyond the bottom of the label. If you want to replicate this, I started with a label 289x122 (w x h), Helvetica as the font and a starting pointSize of 60 which fits comfortably in the label. Here is example output from the standard UILabel and my subclass using the string "{Hg":
I've looked at font descenders and ascenders, tried scaling taking these into account in different combinations, but still haven't had any luck. Any ideas, is this something to do with different fonts having varying descender and ascender lengths?
Your calculation for pointsPerPixel is the wrong way up, it should be...
float pointsPerPixel = self.font.pointSize / size.height;
Also, maybe this code should be in layoutSubviews as the only time the font should be changed is when the frame size changes.
layoutSubviews, but I don't think it works. I think the reason is that assigning a new font to the UILabel subclass triggers another invocation of layoutSubviews, which is problematic. In my implementation, one of my app's queues got locked up.
– user444731
Mar 18 '15 at 16:25
I wonder if its a rounding error inching up to the next larger font size. Could you just scale the rec.size.height slightly? Something like:
float desiredPointSize = rect.size.height *.90 * pointsPerPixel;
Update: Your pointPerPixel calculation is backwards. You're actually dividing pixels by font points, instead of points by Pixels. Swap those and it works every time. Just for thoroughness, here's the sample code I tested:
//text to render
NSString *soString = [NSString stringWithFormat:@"{Hg"];
UIFont *soFont = [UIFont fontWithName:@"Helvetica" size:12];
//box to render in
CGRect rect = soLabel.frame;
//calculate number of pixels used vertically for a given point size.
//We assume that pixel-to-point ratio remains constant.
CGSize size = [soString sizeWithFont:soFont];
float pointsPerPixel;
pointsPerPixel = soFont.pointSize / size.height; //this calc works
//pointsPerPixel = size.height / soFont.pointSize; //this calc does not work
//now calc which fontsize fits in the label
float desiredPointSize = rect.size.height * pointsPerPixel;
UIFont *newFont = [UIFont fontWithName:@"Helvetica" size:desiredPointSize];
//and update the display
[soLabel setFont:newFont];
soLabel.text = soString;
That scaled and fit inside the label box for every size I tested, ranging from 40pt to 60pt fonts. When I reversed the calculation, then I saw the same results with the font being too tall for the box.
