Core Text的CTFramesetterSuggestFrameSizeWithConstraints()每次都返回不正确的大小

Question

根据文档,CTFramesetterSuggestFrameSizeWithConstraints ()"确定字符串范围所需的帧大小".

不幸的是,这个函数返回的大小永远不准确.这是我在做的事情:

    NSAttributedString *string = [[[NSAttributedString alloc] initWithString:@"lorem ipsum" attributes:nil] autorelease];
    CTFramesetterRef framesetter = CTFramesetterCreateWithAttributedString((CFAttributedStringRef) string);
    CGSize textSize = CTFramesetterSuggestFrameSizeWithConstraints(framesetter, CFRangeMake(0,0), NULL, CGSizeMake(rect.size.width, CGFLOAT_MAX), NULL);

返回的大小始终具有正确的宽度计算,但高度始终略短于预期.

这是使用此方法的正确方法吗？

有没有其他方法来布局核心文本？

似乎我不是唯一遇到此方法问题的人.请参阅https://devforums.apple.com/message/181450.

编辑:我使用Quartz测量相同的字符串sizeWithFont:,为属性字符串和Quartz提供相同的字体.以下是我收到的测量数据:

核心文字:133.569336 x 16.592285

石英:135.000000 x 31.000000

Answer 1

试试这个..似乎工作:

+(CGFloat)heightForAttributedString:(NSAttributedString *)attrString forWidth:(CGFloat)inWidth
{
    CGFloat H = 0;

    // Create the framesetter with the attributed string.
    CTFramesetterRef framesetter = CTFramesetterCreateWithAttributedString( (CFMutableAttributedStringRef) attrString); 

    CGRect box = CGRectMake(0,0, inWidth, CGFLOAT_MAX);

    CFIndex startIndex = 0;

    CGMutablePathRef path = CGPathCreateMutable();
    CGPathAddRect(path, NULL, box);

    // Create a frame for this column and draw it.
    CTFrameRef frame = CTFramesetterCreateFrame(framesetter, CFRangeMake(startIndex, 0), path, NULL);

    // Start the next frame at the first character not visible in this frame.
    //CFRange frameRange = CTFrameGetVisibleStringRange(frame);
    //startIndex += frameRange.length;

    CFArrayRef lineArray = CTFrameGetLines(frame);
    CFIndex j = 0, lineCount = CFArrayGetCount(lineArray);
    CGFloat h, ascent, descent, leading;

    for (j=0; j < lineCount; j++)
    {
        CTLineRef currentLine = (CTLineRef)CFArrayGetValueAtIndex(lineArray, j);
        CTLineGetTypographicBounds(currentLine, &ascent, &descent, &leading);
        h = ascent + descent + leading;
        NSLog(@"%f", h);
        H+=h;
    }

    CFRelease(frame);
    CFRelease(path);
    CFRelease(framesetter);


    return H;
}

Answer 2

对于单行框架,请尝试以下方法:

line = CTLineCreateWithAttributedString((CFAttributedStringRef) string);
CGFloat ascent;
CGFloat descent;
CGFloat width = CTLineGetTypographicBounds(line, &ascent, &descent, NULL);
CGFloat height = ascent+descent;
CGSize textSize = CGSizeMake(width,height);

对于多线框架,您还需要添加线条的引线(请参阅" 核心文本编程指南"中的示例代码)

出于某种原因,CTFramesetterSuggestFrameSizeWithConstraints()使用上升和下降的差异来计算高度:

CGFloat wrongHeight = ascent-descent;
CGSize textSize = CGSizeMake(width, wrongHeight);

这可能是一个错误？

我的框架宽度还有其他一些问题; 它值得一试,因为它只在特殊情况下显示.有关更多信息,请参阅此问