在显示文字时，首先计算显示当前的文字需要多宽和多高，然后将对应的UILabel的大小改变成对应的宽度和高度.
该方法的代码如下:
UILabel *introduceLabel= [[UILabel alloc]init];
    CGSize maximumSize = CGSizeMake(screenBounds.size.width-20, 9999);
    NSString *dateString = self.businessInfo[0].vendorsIntroduction;
    UIFont *dateFont = [UIFont fontWithName:@"Helvetica" size:14];
    CGSize dateStringSize = [dateString sizeWithFont:dateFont 
                                   constrainedToSize:maximumSize 
                                       lineBreakMode:introduceLabel.lineBreakMode];
    CGRect dateFrame = CGRectMake(10.0f, 110.0f, screenBounds.size.width-20, dateStringSize.height);
    
    introduceLabel.text = self.businessInfo[0].vendorsIntroduction;
    introduceLabel.font = dateFont;
    introduceLabel.backgroundColor = [UIColor clearColor];
    introduceLabel.lineBreakMode = UILineBreakModeWordWrap;
    introduceLabel.numberOfLines = 0;
    introduceLabel.frame = dateFrame;
    [myscrollview addSubview:introduceLabel];
    [introduceLabel release];