Objective c CtlineGetGlyph使用NSAttributedString运行奇怪的行为

我有一个字符串，比如说，

“Hello”

我需要在前面和后面添加“

”，“

所以字符串看起来像这样：

”，Hello，“

现在我希望文本是白色的，而“，”是不同颜色的。所以我做了这样的事情：

[attributedString addAttribute:(__bridge NSString *)kCTForegroundColorAttributeName value:[UIColor whiteColor] range:NSMakeRange(range.location+1, range.length-1)];
[attributedString addAttribute:(__bridge NSString *)kCTForegroundColorAttributeName value:[UIColor yellowColor] range:NSMakeRange(range.location, 1)];
[attributedString addAttribute:(__bridge NSString *)kCTForegroundColorAttributeName value:[UIColor yellowColor] range:NSMakeRange(range.length-1, 1)];

后来我用

CTFrameSetterRed

，

CGContextRef

CTLineRef line = CFArrayGetValueAtIndex((CFArrayRef)lines, index);
CFArrayRef glyphRuns = CTLineGetGlyphRuns(line);
CFIndex glyphCount = CFArrayGetCount(glyphRuns);

在这个

“，Hello，”

示例中，glyphCount返回

3

！当我将代码更改为：

[attributedString addAttribute:(__bridge NSString *)kCTForegroundColorAttributeName value:[UIColor whiteColor] range:NSMakeRange(range.location+1, range.length-1)];
[attributedString addAttribute:(__bridge NSString *)kCTForegroundColorAttributeName value:[UIColor whiteColor] range:NSMakeRange(range.location, 1)];
[attributedString addAttribute:(__bridge NSString *)kCTForegroundColorAttributeName value:[UIColor whiteColor] range:NSMakeRange(range.length-1, 1)];

（现在整个消息“Hello”是白色的，这是唯一的更改）glyphCount返回

1

为什么会这样？如何避免？这看起来很奇怪