每次核心文本的CTFramesetterSuggestFrameSizeWithConstraints（）返回错误的大小 [英] Core Text's CTFramesetterSuggestFrameSizeWithConstraints() returns incorrect size every time

问题描述

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

According to the docs, CTFramesetterSuggestFrameSizeWithConstraints () "determines the frame size needed for a string range".

不幸的是此函数返回的大小永远都不准确。这是我在做什么：

Unfortunately the size returned by this function is never accurate. Here is what I am doing:

    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);

返回的尺寸始终具有正确的宽度，但是高度始终比预期的要短。

The returned size always has the correct width calculated, however the height is always slightly shorter than what is expected.

这是使用此方法的正确方法吗？

Is this the correct way to use this method?

还有其他方法可以设置核心文本吗？

Is there any other way to layout Core Text?

似乎我不是唯一遇到这种方法问题的人。参见 https://devforums.apple.com/message/181450 。

Seems I am not the only one to run into problems with this method. See https://devforums.apple.com/message/181450.

编辑：
我使用 sizeWithFont：和Quartz测量了相同的字符串，为属性字符串和Quartz提供了相同的字体。以下是我收到的测量结果：

I measured the same string with Quartz using sizeWithFont:, supplying the same font to both the attributed string, and to Quartz. Here are the measurements I received:

核心文字：133.569336 x 16.592285

Core Text: 133.569336 x 16.592285

石英：135.000000 x 31.000000

Quartz: 135.000000 x 31.000000

推荐答案

尝试一下..似乎可行：

try this.. seem to work:

+(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;
}

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