NSString boundingRectWithSize使用CoreText Framesetter缩短剪裁高度？iOS版

Question

我有一个自定义的UIView,它通过CoreText绘制一个NSString:

- (NSMutableAttributedString *)getAttributedString : (NSString *)displayText {
string = [[NSMutableAttributedString alloc]
                                     initWithString:displayText];

helvetica = CTFontCreateWithName(CFSTR("Helvetica"), 20.0, NULL);

[string addAttribute:(id)kCTFontAttributeName
               value:(__bridge id)helvetica
               range:NSMakeRange(0, [string length])];

return string;
}

- (void)drawRect:(CGRect)rect
{

CTFramesetterRef framesetter = CTFramesetterCreateWithAttributedString(
                                                                       (__bridge CFAttributedStringRef)string);
// left column form
leftColumnPath = CGPathCreateMutable();
CGPathAddRect(leftColumnPath, NULL,
              CGRectMake(0, 0,
                         self.bounds.size.width,
                         self.bounds.size.height));

// left column frame
textleftFrame = CTFramesetterCreateFrame(framesetter,
                                     CFRangeMake(0, 0),
                                     leftColumnPath, NULL);

if (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad) {
    // right column form
    rightColumnPath = CGPathCreateMutable();
    CGPathAddRect(rightColumnPath, NULL,
                  CGRectMake(self.bounds.size.width/2.0, 0,
                             self.bounds.size.width/2.0,
                             self.bounds.size.height));

    NSInteger rightColumStart = CTFrameGetVisibleStringRange(textleftFrame).length;

    // right column frame
    textrightFrame = CTFramesetterCreateFrame(framesetter,
                                          CFRangeMake(rightColumStart, 0),
                                          rightColumnPath,
                                          NULL);
}

// flip the coordinate system
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetTextMatrix(context, CGAffineTransformIdentity);
CGContextTranslateCTM(context, 0, self.bounds.size.height);
CGContextScaleCTM(context, 1.0, -1.0);

// draw
CTFrameDraw(textleftFrame, context);
if (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad) {
    CTFrameDraw(textrightFrame, context);
}

// cleanup
CFRelease(textleftFrame);
CGPathRelease(leftColumnPath);
if (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad) {
    CFRelease(textrightFrame);
    CGPathRelease(rightColumnPath);
}
CFRelease(framesetter);
CFRelease(helvetica);
CFRelease(helveticaBold);
}

在另一个类中,我然后尝试使用boundingRectWithSize来计算视图显示文本的时间长度(然后我设置UIScrollView以匹配它):

NSMutableAttributedString * attributedString = [textView getAttributedString:text];

    // Code here for iOS 7.0 - sizeWithFont is deprecated.
    CGRect textBoxSize = [attributedString boundingRectWithSize:CGSizeMake(315.f, CGFLOAT_MAX) options: (NSStringDrawingUsesLineFragmentOrigin|NSStringDrawingUsesFontLeading) context:nil];

    textView.frame = CGRectMake(textView.frame.origin.x, pictureSpace, textBoxSize.size.width, textBoxSize.size.height);

getAttributedString方法在上面.问题是textView的高度略微过短,因此切断了文本的最后一行.任何人都可以提出什么问题？

另外,在旁注中,为什么boundingRectWithSize中的大小必须是315(即略短于屏幕宽度)而不是320才能工作？在320处,textView对于屏幕来说略微过宽.

编辑 - 这似乎只发生在某些字体上 - 例如Verdana工作正常.更有知识的人知道这是否与字形有关吗？

谢谢 !

Answer 1

啊 - 看来 CoreText 的文本间距与boundingBox 方法不同：Core Text 中的行间距如何工作？（为什么它与 NSLayoutManager 不同？）