新的方法采用的是 attributes，attributes参数需要的是一个数组.
我们常用的有几个：
NSMutableParagraphStyle *paragraphStyle = [[NSParagraphStyle defaultParagraphStyle] mutableCopy];
paragraphStyle.lineBreakMode =NSLineBreakByCharWrapping;
NSDictionary *dic=@{
NSFontAttributeName:font,
NSParagraphStyleAttributeName:paragraphStyle,
NSForegroundColorAttributeName:[UIColorlightGrayColor]
};
通过设置 NSParagraphStyleAttributeName，我们可以设置string的段落风格，比如 :
lineBreakMode 段落风格
NSForegroundColorAttributeName 字体颜色
eg：
原先可以这样写：
CGSizesize = [text sizeWithFont:font constrainedToSize:CGSizeMake(300, MAXFLOAT) lineBreakMode:NSLineBreakByCharWrapping];
[text drawInRect:CGRectMake(10,10,300,size.height) withFont:font lineBreakMode:NSLineBreakByCharWrapping];
iOS7 之后需要切换新方法，如下：
NSMutableParagraphStyle *paragraphStyle = [[NSParagraphStyle defaultParagraphStyle] mutableCopy];
paragraphStyle.lineBreakMode = NSLineBreakByCharWrapping;
NSDictionary *attribute=@{
NSFontAttributeName:font,
NSParagraphStyleAttributeName:paragraphStyle
};
CGSizesize= [text boundingRectWithSize:CGSizeMake(300, MAXFLOAT) options:NSStringDrawingUsesLineFragmentOrigin attributes:attribute context:nil].size;
[text drawWithRect:CGRectMake(10,10,300,size.height) options:NSStringDrawingUsesLineFragmentOrigin attributes:attribute context:nil];
