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;
         }