概述，默认显示2行，点击展开按钮，显示所有，点击收回，有显示2行（转载）

项目中有这样的需求，要显示一本书的概述，默认显示2行，点击展开按钮，显示所有，点击收回，有显示2行。

开始的时候按钮事件中，可能写的是这样一段代码：

if (isExpand) {

        [lblBrief setNumberOfLines:2];

        lblBrief.text = [StringUtil subString:strBrief AndSubLength:90];

        [btnBrief setImage:[UIImage imageNamed:@"detailBriefDown"] forState:UIControlStateNormal];

        [btnBrief setImage:[UIImage imageNamed:@"detailBriefDown"] forState:UIControlStateHighlighted];

    }else{

        [lblBrief setNumberOfLines:0];

        lblBrief.text = strBrief;

        [btnBrief setImage:[UIImage imageNamed:@"detailBriefUp"] forState:UIControlStateNormal];

        [btnBrief setImage:[UIImage imageNamed:@"detailBriefUp"] forState:UIControlStateHighlighted];

    }

能够经过setNumberOfLines:0,来让概述的因此内容显示出来，但若是，不计算所要显示所有内容的总高度，label的宽高是不会自动增大的。

else{

        [lblBrief setNumberOfLines:0];

        lblBrief.text = strBrief;

        CGSize constraint = CGSizeMake(self.view.frame.size.width - (15 * 2), 20000.0f);

        

        CGSize size = [strBrief sizeWithFont:[UIFont systemFontOfSize:10]

        

        [brief setFrame:CGRectMake(15,160,size.width,size.height)];

        [btnBrief setImage:[UIImage imageNamed:@"detailBriefUp"]forState:UIControlStateNormal];

        [btnBrief setImage:[UIImage imageNamed:@"detailBriefUp"]forState:UIControlStateHighlighted];

    }