问题
I would like to do a drop cap first character in a UILabel using the attributedText NSAttributedString property only. Like this:
(source: interpretationbydesign.com)
I have experimented with adjusting the base line for the range of the first character to a negative value, and it works for aligning the top of the first char with the top of the rest of the first line. But I have not found any way to make the other lines flow to the right of the drop capped character.
Can this be solved using NSAttributedString only, or do I have to split the string and render it myself using Core Text?
回答1:
CoreText cannot do drop caps because it consists of lines made up of glyph runs. A drop cap would cover multiple lines which is not supported.
To achieve this effect you would have to draw the cap separately and then draw the rest of the text in a path that goes around it.
Long story short: not possible in UILabel, possible, but a fair bit of work with CoreText.
The steps to do it with CoreText are:
- create a framesetter for the single character.
- get its bounds
- create a path that spares out the frame of the drop cap
- create a framesetter for the remaining characters with this path
- draw first glyph
- draw rest
回答2:
As everyone else mentioned, it's not possible to do this with only NSAttributedString. Nikolai has the right approach, using CTFrameSetters. However it is possible to tell the framesetter to render text in a specific area (i.e. defined by a CGPath).
You'll have to create 2 framesetters, one for the drop cap and the other for the rest of the text.
Then, you grab the frame of the drop cap and build a CGPathRef that runs around the space of the frame of the drop cap.
Then, you render both framesetters into your view.
I've created a sample project with an object called DropCapView which is a subclass of UIView. This view renders the first character and wraps the remaining text around it.
It looks like this:
There are quite a few steps, so I've added a link to a github project hosting the example. There are comments in the project that will help you along.
DropCap project on GitHub
You'll have to play around with the shape of the textBox element (i.e. the CGPathRef) for padding around the edges of the view, and to tighten it up to the drop cap letter as well.
Here are the guts of the drawing method:
- (void)drawRect:(CGRect)rect {
//make sure that all the variables exist and are non-nil
NSAssert(_text != nil, @"text is nil");
NSAssert(_textColor != nil, @"textColor is nil");
NSAssert(_fontName != nil, @"fontName is nil");
NSAssert(_dropCapFontSize > 0, @"dropCapFontSize is <= 0");
NSAssert(_textFontSize > 0, @"textFontSize is <=0");
//convert the text aligment from NSTextAligment to CTTextAlignment
CTTextAlignment ctTextAlignment = NSTextAlignmentToCTTextAlignment(_textAlignment);
//create a paragraph style
CTParagraphStyleSetting paragraphStyleSettings[] = { {
.spec = kCTParagraphStyleSpecifierAlignment,
.valueSize = sizeof ctTextAlignment,
.value = &ctTextAlignment
}
};
CFIndex settingCount = sizeof paragraphStyleSettings / sizeof *paragraphStyleSettings;
CTParagraphStyleRef style = CTParagraphStyleCreate(paragraphStyleSettings, settingCount);
//create two fonts, with the same name but differing font sizes
CTFontRef dropCapFontRef = CTFontCreateWithName((__bridge CFStringRef)_fontName, _dropCapFontSize, NULL);
CTFontRef textFontRef = CTFontCreateWithName((__bridge CFStringRef)_fontName, _textFontSize, NULL);
//create a dictionary of style elements for the drop cap letter
NSDictionary *dropCapDict = [NSDictionary dictionaryWithObjectsAndKeys:
(__bridge id)dropCapFontRef, kCTFontAttributeName,
_textColor.CGColor, kCTForegroundColorAttributeName,
style, kCTParagraphStyleAttributeName,
@(_dropCapKernValue) , kCTKernAttributeName,
nil];
//convert it to a CFDictionaryRef
CFDictionaryRef dropCapAttributes = (__bridge CFDictionaryRef)dropCapDict;
//create a dictionary of style elements for the main text body
NSDictionary *textDict = [NSDictionary dictionaryWithObjectsAndKeys:
(__bridge id)textFontRef, kCTFontAttributeName,
_textColor.CGColor, kCTForegroundColorAttributeName,
style, kCTParagraphStyleAttributeName,
nil];
//convert it to a CFDictionaryRef
CFDictionaryRef textAttributes = (__bridge CFDictionaryRef)textDict;
//clean up, because the dictionaries now have copies
CFRelease(dropCapFontRef);
CFRelease(textFontRef);
CFRelease(style);
//create an attributed string for the dropcap
CFAttributedStringRef dropCapString = CFAttributedStringCreate(kCFAllocatorDefault,
(__bridge CFStringRef)[_text substringToIndex:1],
dropCapAttributes);
//create an attributed string for the text body
CFAttributedStringRef textString = CFAttributedStringCreate(kCFAllocatorDefault,
(__bridge CFStringRef)[_text substringFromIndex:1],
textAttributes);
//create an frame setter for the dropcap
CTFramesetterRef dropCapSetter = CTFramesetterCreateWithAttributedString(dropCapString);
//create an frame setter for the dropcap
CTFramesetterRef textSetter = CTFramesetterCreateWithAttributedString(textString);
//clean up
CFRelease(dropCapString);
CFRelease(textString);
//get the size of the drop cap letter
CFRange range;
CGSize maxSizeConstraint = CGSizeMake(200.0f, 200.0f);
CGSize dropCapSize = CTFramesetterSuggestFrameSizeWithConstraints(dropCapSetter,
CFRangeMake(0, 1),
dropCapAttributes,
maxSizeConstraint,
&range);
//create the path that the main body of text will be drawn into
//i create the path based on the dropCapSize
//adjusting to tighten things up (e.g. the *0.8,done by eye)
//to get some padding around the edges of the screen
//you could go to +5 (x) and self.frame.size.width -5 (same for height)
CGMutablePathRef textBox = CGPathCreateMutable();
CGPathMoveToPoint(textBox, nil, dropCapSize.width, 0);
CGPathAddLineToPoint(textBox, nil, dropCapSize.width, dropCapSize.height * 0.8);
CGPathAddLineToPoint(textBox, nil, 0, dropCapSize.height * 0.8);
CGPathAddLineToPoint(textBox, nil, 0, self.frame.size.height);
CGPathAddLineToPoint(textBox, nil, self.frame.size.width, self.frame.size.height);
CGPathAddLineToPoint(textBox, nil, self.frame.size.width, 0);
CGPathCloseSubpath(textBox);
//create a transform which will flip the CGContext into the same orientation as the UIView
CGAffineTransform flipTransform = CGAffineTransformIdentity;
flipTransform = CGAffineTransformTranslate(flipTransform,
0,
self.bounds.size.height);
flipTransform = CGAffineTransformScale(flipTransform, 1, -1);
//invert the path for the text box
CGPathRef invertedTextBox = CGPathCreateCopyByTransformingPath(textBox,
&flipTransform);
CFRelease(textBox);
//create the CTFrame that will hold the main body of text
CTFrameRef textFrame = CTFramesetterCreateFrame(textSetter,
CFRangeMake(0, 0),
invertedTextBox,
NULL);
CFRelease(invertedTextBox);
CFRelease(textSetter);
//create the drop cap text box
//it is inverted already because we don't have to create an independent cgpathref (like above)
CGPathRef dropCapTextBox = CGPathCreateWithRect(CGRectMake(_dropCapKernValue/2.0f,
0,
dropCapSize.width,
dropCapSize.height),
&flipTransform);
CTFrameRef dropCapFrame = CTFramesetterCreateFrame(dropCapSetter,
CFRangeMake(0, 0),
dropCapTextBox,
NULL);
CFRelease(dropCapTextBox);
CFRelease(dropCapSetter);
//draw the frames into our graphic context
CGContextRef gc = UIGraphicsGetCurrentContext();
CGContextSaveGState(gc); {
CGContextConcatCTM(gc, flipTransform);
CTFrameDraw(dropCapFrame, gc);
CTFrameDraw(textFrame, gc);
} CGContextRestoreGState(gc);
CFRelease(dropCapFrame);
CFRelease(textFrame);
}
P.S. this comes with some inspiration from: https://stackoverflow.com/a/9272955/1218605
回答3:
No, this cannot be done with an NSAttributedString and standard string drawing only.
Since the drop cap is a property of a paragraph the CTParagraphStyle would have to contain the information about the drop cap. The only property in CTParagraphStyle that affects indentation of the start of the paragraph is kCTParagraphStyleSpecifierFirstLineHeadIndent, but that affects the first line only.
There's just no way to tell the CTFramesetter how to calculate the beginnings for the second and more rows.
The only way is to define your own attribute and write code to draw the string using CTFramesetter and CTTypesetter that acknowledge this custom attribute.
回答4:
If you're using a UITextView you can use textView.textContainer.exclusionPaths as Dannie P suggested here.
Example in Swift:
class WrappingTextVC: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
let textView = UITextView()
textView.translatesAutoresizingMaskIntoConstraints = false
textView.text = "ropcap example. Lorem ipsum dolor sit amet, consectetur adipiscing elit. Mauris aliquam vulputate ex. Fusce interdum ultricies justo in tempus. Sed ornare justo in purus dignissim, et rutrum diam pulvinar. Quisque tristique eros ligula, at dictum odio tempor sed. Fusce non nisi sapien. Donec libero orci, finibus ac libero ac, tristique pretium ex. Aenean eu lorem ut nulla elementum imperdiet. Ut posuere, nulla ut tincidunt viverra, diam massa tincidunt arcu, in lobortis erat ex sed quam. Mauris lobortis libero magna, suscipit luctus lacus imperdiet eu. Ut non dignissim lacus. Vivamus eget odio massa. Aenean pretium eget erat sed ornare. In quis tortor urna. Quisque euismod, augue vel pretium suscipit, magna diam consequat urna, id aliquet est ligula id eros. Duis eget tristique orci, quis porta turpis. Donec commodo ullamcorper purus. Suspendisse et hendrerit mi. Nulla pellentesque semper nibh vitae vulputate. Pellentesque quis volutpat velit, ut bibendum magna. Morbi sagittis, erat rutrum Suspendisse potenti. Nulla facilisi. Praesent libero est, tincidunt sit amet tempus id, blandit sit amet mi. Morbi sed odio nunc. Mauris lobortis elementum orci, at consectetur nisl egestas a. Pellentesque vel lectus maximus, semper lorem eget, accumsan mi. Etiam semper tellus ac leo porta lobortis."
textView.backgroundColor = .lightGray
textView.textColor = .black
view.addSubview(textView)
textView.leadingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.leadingAnchor, constant: 20).isActive = true
textView.trailingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.trailingAnchor, constant: -20).isActive = true
textView.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor, constant: 20).isActive = true
textView.bottomAnchor.constraint(equalTo: view.safeAreaLayoutGuide.bottomAnchor, constant: -40).isActive = true
let dropCap = UILabel()
dropCap.text = "D"
dropCap.font = UIFont.boldSystemFont(ofSize: 60)
dropCap.backgroundColor = .lightText
dropCap.sizeToFit()
textView.addSubview(dropCap)
textView.textContainer.exclusionPaths = [UIBezierPath(rect: dropCap.frame)]
}
}
Result:
Full example on github
回答5:
Not a perfect solution, but you should give DTCoreText a try and render your normal NSString as an formatted HTML. Within HTML it is possible to "Drop cap" a letter.
来源：https://stackoverflow.com/questions/14214900/drop-cap-with-nsattributedstring