Swift计算字符串高度,宽度,size方法

计算字符串的高度
swift的原生方法名，基本跟OC一致

OC旧方法, 用了会警告

    CGSize size = [self.message sizeWithFont:[UIFont systemFontOfSize:17] constrainedToSize:CGSizeMake(200, 9999)];

OC新方法

    CGSize size = [topicModel.content boundingRectWithSize:CGSizeMake(278, MAXFLOAT) options: NSStringDrawingUsesLineFragmentOrigin attributes:@{NSFontAttributeName:[UIFont systemFontOfSize:15]} context:nil].size;

swift

    boundingRectWithSize(size: CGSize, options: NSStringDrawingOptions, attributes: [NSObject : AnyObject]!, context: NSStringDrawingContext!) -> CGRect

例

    var size = CGRect();    var size2 = CGSize();    size = string.boundingRectWithSize(size2, options: NSStringDrawingOptions.UsesFontLeading, attributes: nil, context: nil);