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);