由于Value属性本身可能包含多个值，您无法使用==运算符将其与特定字符串直接比较。请改用Contains()：

.....
if (item.Value.Contains("test"))
{
    .....
}

...或在方法链版本中：

string nodePointingToThisOne = dic.Where(x => x.Value.Contains("test"))
                                  .Select(x => x.Key)
                                  .FirstOrDefault();

尝试按Keys进行迭代，然后比较值，仅当Value匹配时才返回Key。
就像这样：

foreach (var key in dic.Keys)
{
    if(dic[key].Contains("your value"))
        return key;
}

可以像这样迭代键

foreach (var key in dic.Keys)
    {
        if(key == "your key")
            return key;
    }

您还可以像这样迭代值

foreach (var v in dic.Values)
    {
        if(v == "your value")
            return v;
    }

• • 示例：**

Dictionary<string, string> c = new Dictionary<string, string>();
        c.Add("Pk", "Pakistan");
        c.Add("Aus", "Australia");
        c.Add("Ind", "India");
        c.Add("Nz", "New Zeland");
        c.Add("SA", "South Africa");

        foreach (var v in c.Values)
        {
            if (v == "Australia")
            {
                 Console.WriteLine("Your Value is = " + v);
                // perform your task 
            }
        }

        foreach (var k in c.Keys)
        {
            if (k == "Aus")
            {
                // perform your task    
                Console.WriteLine("Your Key is = " + k);
            }
        }

• • 输出：**

您的值为="澳大利亚"
您的密钥为="Aus"

如果你看一下MultiValueDictionary,，第81行会给予你一个提示，它是：

[TestInitialize]
 public void TestInitialize()
 {
     MultiValueDictionary = new MultiValueDictionary<TestKey, string>();
 }

 protected static void AssertAreEqual( IDictionary<TestKey, string[]> expected,
 IMultiValueDictionary<TestKey, string> actual )
 {
     Assert.AreEqual( expected.Count, actual.Count );
     foreach ( var k in expected.Keys )
     {
         var expectedValues = expected[ k ];
         var actualValues = actual[ k ];
         AssertAreEqual( expectedValues, actualValues );
     }
 }

因此，对于您的情况，解决方案类似：

foreach (var item in dic.keys)
{
    if(dict[item] == "test")
    {
        nodePointingToThisOne = item;
        return nodePointingToThisOne;
    }
}

为我工作：

foreach (int i in Dictionary.Keys)
{
   if (Dictionary.Values.ToString() == "Your Value")
   {
      return Dictionary.Keys;
   }
}