UILabel size incorrect for single line of text with lineSpacing and multiple colors

问题

I'm pretty sure this is actually a UIKit bug but want to get some input to see if I'm missing something silly here.

Here is the code I have:

// single line with modified line spacing and 2 colors - broken, line spacing is added to the bottom!
UILabel *brokenLabel = [[UILabel alloc] init];
brokenLabel.backgroundColor = [UIColor greenColor];

NSMutableAttributedString *attributedString = [[NSMutableAttributedString alloc] initWithString:@"Just some text"];

[attributedString addAttributes:@{NSForegroundColorAttributeName : [UIColor redColor]} range:[attributedString.string rangeOfString:@"text"]];

attributedString = attributedStringFromAttributedStringWithLineSpacing(attributedString, 20, NSTextAlignmentCenter);

brokenLabel.attributedText = attributedString;
[brokenLabel sizeToFit];
brokenLabel.frame = CGRectOffset(brokenLabel.frame, 50, 100);
[self.view addSubview:brokenLabel];
// end

// single line with modified line spacing and 1 color - correct
UILabel *workingLabel = [[UILabel alloc] init];
workingLabel.backgroundColor = [UIColor greenColor];

attributedString = [[NSMutableAttributedString alloc] initWithString:@"Just some text"];

attributedString = attributedStringFromAttributedStringWithLineSpacing(attributedString, 20, NSTextAlignmentCenter);

workingLabel.attributedText = attributedString;
[workingLabel sizeToFit];
workingLabel.frame = CGRectOffset(workingLabel.frame, 200, 100);
[self.view addSubview:workingLabel];
//end

// multiple lines with modified line spacing and 1 color - correct
UILabel *workingLabel2 = [[UILabel alloc] init];
workingLabel2.frame = CGRectMake(0, 0, 100, 0);
workingLabel2.numberOfLines = 0;
workingLabel2.backgroundColor = [UIColor greenColor];

attributedString = [[NSMutableAttributedString alloc] initWithString:@"Just some text"];

attributedString = attributedStringFromAttributedStringWithLineSpacing(attributedString, 20, NSTextAlignmentCenter);

workingLabel2.attributedText = attributedString;
[workingLabel2 sizeToFit];
workingLabel2.frame = CGRectOffset(workingLabel2.frame, 50, 300);
[self.view addSubview:workingLabel2];
//end

// multiple lines with modified line spacing and 2 color - correct
UILabel *workingLabel3 = [[UILabel alloc] init];
workingLabel3.frame = CGRectMake(0, 0, 100, 0);
workingLabel3.numberOfLines = 0;
workingLabel3.backgroundColor = [UIColor greenColor];

attributedString = [[NSMutableAttributedString alloc] initWithString:@"Just some text"];

[attributedString addAttributes:@{NSForegroundColorAttributeName : [UIColor redColor]} range:[attributedString.string rangeOfString:@"text"]];

attributedString = attributedStringFromAttributedStringWithLineSpacing(attributedString, 20, NSTextAlignmentCenter);

workingLabel3.attributedText = attributedString;
[workingLabel3 sizeToFit];
workingLabel3.frame = CGRectOffset(workingLabel3.frame, 200, 300);
[self.view addSubview:workingLabel3];

along with a simple convenience function to change the lineSpacing of an attributed string:

NSMutableAttributedString *attributedStringFromAttributedStringWithLineSpacing(NSAttributedString *string, CGFloat lineSpacing, NSTextAlignment textAlignment)
{
    NSMutableAttributedString *mutable = string.mutableCopy;

    NSMutableParagraphStyle *par = [NSMutableParagraphStyle new];
    par.alignment = textAlignment;
    par.lineSpacing = lineSpacing;
    [mutable addAttributes:@{NSParagraphStyleAttributeName : par} range:NSMakeRange(0, mutable.length)];
    return mutable;
}

However, this is what it looks like

As you can see, the height of the first label is way too big (or the height that it should be + my custom line spacing, to be precise). When simply adding another color to the first attributed string, it causes the sizeToFit size to increase by adding the lineSpacing below it. I also tried using the boundingRectWithSize: methods on the strings directly and the same issue is visible. So this is not specific to the label sizing code but is an issue with the strings themselves. I don't see any possible reason why this should be happening. Does anyone have any insight?

回答1:

In your Attributes Dictionary add

 [attrDic setObject:@0 forKey:NSBaselineOffsetAttributeName];

来源：https://stackoverflow.com/questions/23575958/uilabel-size-incorrect-for-single-line-of-text-with-linespacing-and-multiple-col