iOS之動態計算文字的高度

+ (CGSize)boundingALLRectWithSize:(NSString *)txt Font:(UIFont *)font Size:(CGSize)size {    
    NSMutableAttributedString *attributedString = [[NSMutableAttributedString alloc] initWithString:txt];
    NSMutableParagraphStyle *style = [[NSMutableParagraphStyle alloc] init];
    [style setLineSpacing:2.0f];//切記LineSapcing >= 2,不然會顯示不全
    [attributedString addAttribute:NSParagraphStyleAttributeName value:style range:NSMakeRange(0, [txt length])];
    
    CGSize realSize = CGSizeZero;

#if __IPHONE_OS_VERSION_MAX_ALLOWED > __IPHONE_6_1
    CGRect textRect = [txt boundingRectWithSize:size options:NSStringDrawingUsesLineFragmentOrigin attributes:@{NSFontAttributeName:font, NSParagraphStyleAttributeName:style} context:nil];
    realSize = textRect.size;
#else
    realSize = [txt sizeWithFont:font constrainedToSize:size];
#endif
    
    realSize.width = ceilf(realSize.width);
    realSize.height = ceilf(realSize.height);
    return realSize;
}

調用：float strHeight = [Util boundingALLRectWithSize:str Font:[UIFont systemFontOfSize:14] Size:CGSizeMake(SCREEN_WIDTH-24, MAXFLOAT)].height;