boundingRectWithSize 的使用, 计算UILable高度, 包含Emoji及多属性string.

iOS的文字高度计算一直是个问题, 苹果也一直在改, 这几天看了一下 boundingRectWithSize 方法.

- (CGRect)boundingRectWithSize:(CGSize)size options:(NSStringDrawingOptions)options context:(NSStringDrawingContext *)context NS_AVAILABLE_IOS(6_0);

　　
踩了几个坑后, 总算找到比较好的使用方法.

参考: http://stackoverflow.com/questions/13621084/boundingrectwithsize-for-nsattributedstring-returning-wrong-size 使用时的注意事项:
1: NSAttributedString 的每个部分都要至少设置两个属性:
NSFontAttributeName
NSForegroundColorAttributeName

2: NSStringDrawingOptions 的值, 在多行的情况下, 至少要有
NSStringDrawingUsesLineFragmentOrigin
NSStringDrawingUsesFontLeading

3: 如果文字中可能会出现emoji表情的话, emoji的高度比文字要高一点点,
我的方便是简单的在高度基础上加了两个像素.
(用CoreText可能会好一些, 但相对复杂.)

附代码:

NSMutableAttributedString *attrStr = [[NSMutableAttributedString alloc] initWithString:fullDescAndTagStr];

NSRange allRange = [fullDescAndTagStr rangeOfString:fullDescAndTagStr];

[attrStr addAttribute:NSFontAttributeName

value:[UIFont systemFontOfSize:13.0]

range:allRange];

[attrStr addAttribute:NSForegroundColorAttributeName

value:[UIColor blackColor]

range:allRange];

NSRange destRange = [fullDescAndTagStr rangeOfString:tagStr];

[attrStr addAttribute:NSForegroundColorAttributeName

value:HEXCOLOR(0x009cdd)

range:destRange];

CGFloat titleHeight;

NSStringDrawingOptions options =  NSStringDrawingUsesLineFragmentOrigin | NSStringDrawingUsesFontLeading;

CGRect rect = [attrStr boundingRectWithSize:CGSizeMake(labelWidth, CGFLOAT_MAX)

options:options

context:nil];

titleHeight = ceilf(rect.size.height);

return titleHeight+2;  // 加两个像素,防止emoji被切掉.