原文：http://www.docin.com/p-721844449.html
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UIFont *font = [UIFont fontWithName:@"PingFangSC-Regular"size:15.f] ?: [UIFont systemFontOfSize:14.f];
CGFloat ascender = font.ascender;
CGFloat descender = font.descender;
CGFloat pointSize = font.pointSize;
CGFloat lineHeight = font.lineHeight;
CGFloat capHeight = font.capHeight;
CGFloat xHeight = font.xHeight;
CGFloat leading = font.leading;
