How to make NSStringDrawingContext shrink text?

Question

I'm trying to use the attributed string API of iOS 6 to calculate the size of text and shrink the font size if necessary. However, I can't get it to work as the documentation says.

NSString *string = @"This is a long text that doesn't shrink as it should";

NSStringDrawingContext *context = [NSStringDrawingContext new];
context.minimumScaleFactor = 0.5;

UIFont *font = [UIFont fontWithName:@"SourceSansPro-Bold" size:32.f];

NSMutableParagraphStyle *paragraphStyle = [NSMutableParagraphStyle new];
paragraphStyle.lineBreakMode = NSLineBreakByClipping;

NSDictionary *attributes = @{ NSFontAttributeName: font,
                              NSParagraphStyleAttributeName: paragraphStyle };

NSAttributedString *attributedString = [[NSAttributedString alloc] initWithString:self.title attributes:attributes];

CGRect rect = [attributedString boundingRectWithSize:CGSizeMake(512.f, 512.f) options:NSStringDrawingUsesLineFragmentOrigin context:context];

NSLog(@"rect: %@, context: %@", NSStringFromCGRect(rect), context.debugDescription);

But the text doesn't shrink and is truncated. actualScaleFactor is always 1. The log results are:

rect:{{0, 0}, {431.64801, 80.447998}}, context:<NSStringDrawingContext: 0x14e85770> minimumScaleFactor:0.500000 minimumTrackingAdjustment:0.000000 actualScaleFactor:1.000000 actualTrackingAdjustment:0.000000 totalBounds:{{0, 0}, {431.64801, 80.447998}}

The result is the same if I use the actual drawing method and not the measuring method. If I remove the paragraph style, it makes the text wrap and doesn't shrink it. If I remove the paragraph style AND I choose a size that only allows one line of text, the text is truncated too instead of being shrunk. What is wrong? There is very little documentation or online resources dealing with NSStringDrawingContext. And I'm trying to avoid the use of sizeWithFont:minFontSize:actualFontSize:forWidth:lineBreakMode: which is deprecated in iOS 7.

Answer 1

NSStringDrawingContext's minimumScaleFactor appears to be broken in iOS 7.

As far as I can make out, even in iOS 6, it didn't work for drawing; it worked for measuring, so you could work out what would happen in a context where it does work for drawing, like a UILabel. That way, you know the correct minimum height for the label.

Or, you could use the resulting scale factor to shrink the text yourself, in the knowledge that now it will fit.

Example:

- (void)drawRect:(CGRect)rect
{
    // rect is 0,0,210,31

    NSMutableAttributedString* s = 
        [[NSMutableAttributedString alloc] initWithString: @"This is the army Mister Jones."];
    [s addAttributes:@{NSFontAttributeName:[UIFont fontWithName:@"GillSans" size:20]} 
        range:NSMakeRange(0,s.length)];

    NSMutableParagraphStyle* para = [[NSMutableParagraphStyle alloc] init];
    para.lineBreakMode = NSLineBreakByTruncatingTail;
    [s addAttributes:@{NSParagraphStyleAttributeName:para} 
        range:NSMakeRange(0,s.length)];

    NSStringDrawingContext* con = [[NSStringDrawingContext alloc] init];
    con.minimumScaleFactor = 0.5;

    CGRect result = 
        [s boundingRectWithSize:rect.size 
            options:NSStringDrawingUsesLineFragmentOrigin context:con];
    CGFloat scale = con.actualScaleFactor;
    // ...(could have a check here to see if result fits in target rect)...

    // fix font to use scale factor, and draw
    [s addAttributes:@{NSFontAttributeName:[UIFont fontWithName:@"GillSans" size:20*scale]} 
        range:NSMakeRange(0,s.length)];
    [s drawWithRect:rect options:NSStringDrawingUsesLineFragmentOrigin context:nil];

}

In iOS 6, scale is about 0.85 and you can use it as shown to shrink the text. But in iOS 7, scale remains at 1, suggesting that no shrinkage is happening and this feature of NSStringDrawingContext is now useless. I can't tell whether that's a bug or whether the feature has been deliberately abandoned.