我想仅使用 attributedText NSAttributedString 属性在 UILabel 中设置首字下沉第一个字符。像这样:

_{(来源:interpretationbydesign.com)}

我已经尝试将第一个字符范围的基线调整为负值，并且它适用于将第一个字符的顶部与第一行其余部分的顶部对齐。但我还没有找到任何方法让其他行流到下沉字符的右侧。

这可以仅使用 NSAttributedString 来解决吗，还是我必须拆分字符串并使用 Core Text 自己呈现它？

最佳答案

正如其他人所提到的，仅使用 NSAttributedString 是不可能做到这一点的。 Nikolai 有正确的方法，使用 CTFrameSetters。但是，可以告诉框架 setter 在特定区域(即由 CGPath 定义)中呈现文本。

您必须创建 2 个框架 setter ，一个用于首字下沉，另一个用于文本的其余部分。

然后，您捕获首字下沉的框架并构建一个围绕首字下沉框架空间运行的 CGPathRef。

然后，您将两个框架 setter 渲染到您的 View 中。

我创建了一个示例项目，其中包含一个名为 DropCapView 的对象，它是 UIView 的子类。此 View 呈现第一个字符并将其余文本环绕在其周围。

看起来像这样:

有相当多的步骤，所以我添加了指向托管该示例的 github 项目的链接。项目中有评论可以帮助您。

DropCap project on GitHub

您必须尝试使用​​ textBox 元素(即 CGPathRef)的形状来填充 View 的边缘，并将其收紧到首字下沉字母.

下面是绘图方法的内容:

- (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);
}

附言这来自于一些灵感:https://stackoverflow.com/a/9272955/1218605

关于ios - 带 NSAttributedString 的首字下沉，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/14214900/