C#合并两个Dictionary的方法

直接代码：

 public Dictionary<string, string> MergeDictionary(Dictionary<string, string> first, Dictionary<string, string> second)
        {
            if (first == null) first = new Dictionary<string, string>();
            if (second == null) return first;

            foreach (var item in second)
            {
                 if (!first.ContainsKey(item.Key))
                     first.Add(item.Key, item.Value);                
            }

            return first;
        }

第二种：

 public Dictionary<string, string> MergeDictionary(Dictionary<string, string> first, Dictionary<string, string> second)
        {
            if (first == null) first = new Dictionary<string, string>();
            if (second == null) return first;

            //相对于第一种只是修改了遍历的方法
            foreach (string key in second.Keys)
            {
                if (!first.ContainsKey(key))
                    first.Add(key,second[key]);
            }
            return first;
        }