动态计算 UILabel 的高度的代码

旧方法：

  self.bookInfoRecCentLab.text = summaryStr;

        self.bookInfoRecCentLab.font = 0;

        size1 = [summaryStr sizeWithFont:[UIFont systemFontOfSize:15] constrainedToSize:CGSizeMake(bookInfoCentLabW, 900)];

        self.bookInfoRecCentLab.font = [UIFont systemFontOfSize:15];

新方法：

    CGSize size_1=CGSizeMake(280, 200);

    NSString *detailString=@"简洁打算将开放和大厦开奖号爱的色放空间哈斯短发科技爱的色放离开";

    NSDictionary *dic1=[NSDictionary dictionaryWithObject:[UIFont systemFontOfSize:12] forKey:NSFontAttributeName];

    _size1=[detailString boundingRectWithSize:size_1 options:NSStringDrawingUsesLineFragmentOrigin|NSStringDrawingUsesFontLeading attributes:dic1 context:nil].size;