UILabel *hah = [[UILabel alloc]initWithFrame:CGRectMake(100, 15, 100, 0)];
    hah.font = [UIFont systemFontOfSize:100];
    hah.text = @"fffff";
    hah.backgroundColor = [UIColor blueColor];
    [hah sizeToFit];
    [label addSubview:hah];
    
    CGRect titleRect = [@"fffffffawgawdpumkjff" boundingRectWithSize:CGSizeMake(MAXFLOAT, 20) options:NSStringDrawingUsesLineFragmentOrigin attributes:@{NSFontAttributeName:[UIFont systemFontOfSize:100]} context:nil];
    
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2.0 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
        NSLog(@"---- %f  %f",titleRect.size.width,titleRect.size.height);
        NSLog(@"----pointSize: %f height: %f  ascender: %f  descender: %f   capHeight: %f   xHeight: %f   lineHeight: %f   leading: %f",hah.font.pointSize,hah.frame.size.height,hah.font.ascender,hah.font.descender,hah.font.capHeight,hah.font.xHeight,hah.font.lineHeight,hah.font.leading);
    });

测试发现  单行 .font.lineHeight == titleRect.size.height
  ascender + descender = lineHeight

苹果的descender 与 descent的值是不一样的

1688086-dc9d65ae561579ed.png