blocks|key|396915|text|可以，您可以使用Linq检查AllKeys属性：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|396916|using+System.Linq;
...
collection.AllKeys.Contains(key);|code-block|syntax|javascript|396917|然而，Dictionary<string,+string[]>可能更适合于此目的，可能是通过扩展方法创建的：|396918|public+static+void+Dictionary<string,+string[]>+ToDictionary(this+NameValueCollection+collection)+
{
++++return+collection.Cast<string>().ToDictionary(key+=>+key,+key+=>+collection.GetValues(key));
}

var+dictionary+=+collection.ToDictionary();
if+(dictionary.ContainsKey(key))
{
+++...
}|396919|entityMap^0|E|7|0|0|3|S|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|T|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|U|8|@$9|V|A|W|B|C]]|D|@]|E|$]]|$1|M|3|N|5|H|7|X|8|@]|D|@]|E|$I|J]]|$1|O|3|-4|5|6|7|Y|8|@]|D|@]|E|$]]]|P|$]]

Yes, you can use Linq to check the <code>AllKeys</code> property:

<pre><code>using System.Linq;
...
collection.AllKeys.Contains(key);
</code></pre>

However a <code>Dictionary&lt;string, string[]&gt;</code> would be far more suited to this purpose, perhaps created via an extension method:

<pre><code>public static void Dictionary&lt;string, string[]&gt; ToDictionary(this NameValueCollection collection) 
{
 return collection.Cast&lt;string&gt;().ToDictionary(key =&gt; key, key =&gt; collection.GetValues(key));
}

var dictionary = collection.ToDictionary();
if (dictionary.ContainsKey(key))
{
 ...
}
</code></pre>

blocks|key|613036|text|您可以使用Get方法并检查null，因为如果NameValueCollection不包含指定的键，该方法将返回null。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|613037|参见MSDN。|613038|entityMap|0|LINK|mutability|MUTABLE|url|http://msdn.microsoft.com/en-us/library/s8e7f4s6.aspx^0|5|3|D|4|1J|4|0|2|4|0|0^^$0|@$1|2|3|4|5|6|7|P|8|@$9|Q|A|R|B|C]|$9|S|A|T|B|C]|$9|U|A|V|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|W|8|@]|D|@$9|X|A|Y|1|Z]]|E|$]]|$1|H|3|-4|5|6|7|10|8|@]|D|@]|E|$]]]|I|$J|$5|K|L|M|E|$N|O]]]]

You could use the <code>Get</code> method and check for <code>null</code> as the method will return <code>null</code> if the NameValueCollection does not contain the specified key.

See <a href="http://msdn.microsoft.com/en-us/library/s8e7f4s6.aspx" rel="nofollow">MSDN</a>.

blocks|key|396976|text|使用此方法：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|396977|private+static+bool+ContainsKey(this+NameValueCollection+collection,+string+key)
{
++++if+(collection.Get(key)+==+null)
++++{
++++++++return+collection.AllKeys.Contains(key);
++++}

++++return+true;
}|code-block|syntax|javascript|396978|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Use this method:
<pre><code>private static bool ContainsKey(this NameValueCollection collection, string key)
{
 if (collection.Get(key) == null)
 {
 return collection.AllKeys.Contains(key);
 }

 return true;
}
</code></pre>

blocks|key|397055|text|如果集合大小较小，您可以使用rich.okelly提供的解决方案。但是，较大的集合意味着字典的生成可能比仅搜索关键字集合的速度慢得多。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|397056|此外，如果您的使用场景是在不同的时间点搜索密钥，其中NameValueCollection可能已被修改，则每次生成字典可能比仅搜索密钥集合慢。|397057|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

If the collection size is small you could go with the solution provided by rich.okelly. However, a large collection means that the generation of the dictionary may be noticeably slower than just searching the keys collection. 

Also, if your usage scenario is searching for keys in different points in time, where the NameValueCollection may have been modified, generating the dictionary each time may, again, be slower than just searching the keys collection.

blocks|key|397127|text|我不认为这些答案中的任何一个都是非常正确/最优的。NameValueCollection不仅不区分空值和缺失值，而且它的键也不区分大小写。因此，我认为一个完整的解决方案应该是：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|397128|public+static+bool+ContainsKey(this+NameValueCollection+@this,+string+key)
{
++++return+@this.Get(key)+!=+null+
++++++++//+I'm+using+Keys+instead+of+AllKeys+because+AllKeys,+being+a+mutable+array,
++++++++//+can+get+out-of-sync+if+mutated+(it+weirdly+re-syncs+when+you+modify+the+collection).
++++++++//+I'm+also+not+100%25+sure+that+OrdinalIgnoreCase+is+the+right+comparer+to+use+here.
++++++++//+The+MSDN+docs+only+say+that+the+"default"+case-insensitive+comparer+is+used
++++++++//+but+it+could+be+current+culture+or+invariant+culture
++++++++%7C%7C+@this.Keys.Cast<string>().Contains(key,+StringComparer.OrdinalIgnoreCase);
}|code-block|syntax|javascript|397129|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

I don't think any of these answers are quite right/optimal. NameValueCollection not only doesn't distinguish between null values and missing values, it's also case-insensitive with regards to it's keys. Thus, I think a full solution would be:

<pre><code>public static bool ContainsKey(this NameValueCollection @this, string key)
{
 return @this.Get(key) != null 
 // I'm using Keys instead of AllKeys because AllKeys, being a mutable array,
 // can get out-of-sync if mutated (it weirdly re-syncs when you modify the collection).
 // I'm also not 100% sure that OrdinalIgnoreCase is the right comparer to use here.
 // The MSDN docs only say that the "default" case-insensitive comparer is used
 // but it could be current culture or invariant culture
 || @this.Keys.Cast&lt;string&gt;().Contains(key, StringComparer.OrdinalIgnoreCase);
}
</code></pre>

blocks|key|613181|text|这也可以是一种不需要引入新方法的解决方案：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|613182|++++item+=+collection["item"]+!=+null+?+collection["item"].ToString()+:+null;|code-block|syntax|javascript|613183|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

This could also be a solution without having to introduce a new method:

<pre><code> item = collection["item"] != null ? collection["item"].ToString() : null;
</code></pre>

blocks|key|397225|text|正如您在参考资料中所看到的，NameValueCollection继承自NameObjectCollectionBase。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|397226|因此，您可以使用base-type，通过反射获取私有哈希表，并检查它是否包含特定的键。|397227|为了让它在Mono中也能工作，您需要查看哈希表的名称是mono，这是您可以看到的here+(m_ItemsContainer)，并且如果初始FieldInfo为null+(单运行时)，则获取mono字段。|397228|像这样|397229|public+static+class+ParameterExtensions
{

++++private+static+System.Reflection.FieldInfo+InitFieldInfo()
++++{
++++++++System.Type+t+=+typeof(System.Collections.Specialized.NameObjectCollectionBase);
++++++++System.Reflection.FieldInfo+fi+=+t.GetField("_entriesTable",+System.Reflection.BindingFlags.Instance+%7C+System.Reflection.BindingFlags.NonPublic);

++++++++if(fi+==+null)+//+Mono
++++++++++++fi+=+t.GetField("m_ItemsContainer",+System.Reflection.BindingFlags.Instance+%7C+System.Reflection.BindingFlags.NonPublic);

++++++++return+fi;
++++}

++++private+static+System.Reflection.FieldInfo+m_fi+=+InitFieldInfo();


++++public+static+bool+Contains(this+System.Collections.Specialized.NameValueCollection+nvc,+string+key)
++++{
++++++++//System.Collections.Specialized.NameValueCollection+nvc+=+new+System.Collections.Specialized.NameValueCollection();
++++++++//nvc.Add("hello",+"world");
++++++++//nvc.Add("test",+"case");

++++++++//+The+Hashtable+is+case-INsensitive
++++++++System.Collections.Hashtable+ent+=+(System.Collections.Hashtable)m_fi.GetValue(nvc);
++++++++return+ent.ContainsKey(key);
++++}
}|code-block|syntax|javascript|397230|对于超纯、无反射的.NET+2.0代码，您可以循环遍历键，而不是使用哈希表，但这很慢。|397231|private+static+bool+ContainsKey(System.Collections.Specialized.NameValueCollection+nvc,+string+key)
{
++++foreach+(string+str+in+nvc.AllKeys)
++++{
++++++++if+(System.StringComparer.InvariantCultureIgnoreCase.Equals(str,+key))
++++++++++++return+true;
++++}

++++return+false;
}|397232|entityMap|0|LINK|mutability|MUTABLE|url|http://referencesource.microsoft.com/#System/compmod/system/collections/specialized/namevaluecollection.cs|1|http://referencesource.microsoft.com/#System/compmod/system/collections/specialized/nameobjectcollectionbase.cs,d5a7f1ad2a09df6f|2|https://github.com/mono/mono/blob/master/mcs/tools/cil-strip/Mono.Cecil/NameObjectCollectionBase.cs^0|E|J|0|10|O|1|0|0|14|4|2|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|14|8|@]|9|@$A|15|B|16|1|17]|$A|18|B|19|1|1A]]|C|$]]|$1|D|3|E|5|6|7|1B|8|@]|9|@]|C|$]]|$1|F|3|G|5|6|7|1C|8|@]|9|@$A|1D|B|1E|1|1F]]|C|$]]|$1|H|3|I|5|6|7|1G|8|@]|9|@]|C|$]]|$1|J|3|K|5|L|7|1H|8|@]|9|@]|C|$M|N]]|$1|O|3|P|5|6|7|1I|8|@]|9|@]|C|$]]|$1|Q|3|R|5|L|7|1J|8|@]|9|@]|C|$M|N]]|$1|S|3|-4|5|6|7|1K|8|@]|9|@]|C|$]]]|T|$U|$5|V|W|X|C|$Y|Z]]|10|$5|V|W|X|C|$Y|11]]|12|$5|V|W|X|C|$Y|13]]]]

As you can see in the reference sources, <a href="http://referencesource.microsoft.com/#System/compmod/system/collections/specialized/namevaluecollection.cs" rel="nofollow">NameValueCollection</a> inherits from <a href="http://referencesource.microsoft.com/#System/compmod/system/collections/specialized/nameobjectcollectionbase.cs,d5a7f1ad2a09df6f" rel="nofollow">NameObjectCollectionBase</a>. 

So you take the base-type, get the private hashtable via reflection, and check if it contains a specific key.

For it to work in Mono as well, you need to see what the name of the hashtable is in mono, which is something you can see <a href="https://github.com/mono/mono/blob/master/mcs/tools/cil-strip/Mono.Cecil/NameObjectCollectionBase.cs" rel="nofollow">here</a> (m_ItemsContainer), and get the mono-field, if the initial FieldInfo is null (mono-runtime).

Like this

<pre><code>public static class ParameterExtensions
{

 private static System.Reflection.FieldInfo InitFieldInfo()
 {
 System.Type t = typeof(System.Collections.Specialized.NameObjectCollectionBase);
 System.Reflection.FieldInfo fi = t.GetField("_entriesTable", System.Reflection.BindingFlags.Instance | System.Reflection.BindingFlags.NonPublic);

 if(fi == null) // Mono
 fi = t.GetField("m_ItemsContainer", System.Reflection.BindingFlags.Instance | System.Reflection.BindingFlags.NonPublic);

 return fi;
 }

 private static System.Reflection.FieldInfo m_fi = InitFieldInfo();


 public static bool Contains(this System.Collections.Specialized.NameValueCollection nvc, string key)
 {
 //System.Collections.Specialized.NameValueCollection nvc = new System.Collections.Specialized.NameValueCollection();
 //nvc.Add("hello", "world");
 //nvc.Add("test", "case");

 // The Hashtable is case-INsensitive
 System.Collections.Hashtable ent = (System.Collections.Hashtable)m_fi.GetValue(nvc);
 return ent.ContainsKey(key);
 }
}
</code></pre>

for ultra-pure non-reflective .NET 2.0 code, you can loop over the keys, instead of using the hash-table, but that is slow.

<pre><code>private static bool ContainsKey(System.Collections.Specialized.NameValueCollection nvc, string key)
{
 foreach (string str in nvc.AllKeys)
 {
 if (System.StringComparer.InvariantCultureIgnoreCase.Equals(str, key))
 return true;
 }

 return false;
}
</code></pre>

blocks|key|397289|text|在VB中，它是：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|397290|if+not+MyNameValueCollection(Key)+is+Nothing+then
.......
end+if|code-block|syntax|javascript|397291|在C#中应该是：|397292|if+(MyNameValueCollection(Key)+!=+null)+{+}|397293|我不确定它应该是null还是""，但这应该会有所帮助。|offset|length|style|CODE|397294|entityMap^0|0|0|0|0|8|4|E|2|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|W|8|@$M|X|N|Y|O|P]|$M|Z|N|10|O|P]]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|11|8|@]|9|@]|A|$]]]|R|$]]

In VB it's:

<pre><code>if not MyNameValueCollection(Key) is Nothing then
.......
end if
</code></pre>

In C# should just be:

<pre><code>if (MyNameValueCollection(Key) != null) { }
</code></pre>

Not sure if it should be <code>null</code> or <code>""</code> but this should help.

blocks|key|613352|text|NameValueCollection+n+=+Request.QueryString;

if+(n.HasKeys())
+++{
+++++++//something
+++}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|613353|返回值类型:如果NameValueCollection包含非空的键，则返回System.Boolean+true；否则返回false。LINK|unstyled|offset|length|613354|entityMap|0|LINK|mutability|MUTABLE|url|https://msdn.microsoft.com/en-us/library/system.collections.specialized.namevaluecollection.haskeys(v=vs.110).aspx^0|0|1V|4|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|R|8|@]|9|@$G|S|H|T|1|U]]|A|$]]|$1|I|3|-4|5|F|7|V|8|@]|9|@]|A|$]]]|J|$K|$5|L|M|N|A|$O|P]]]]

<pre><code>NameValueCollection n = Request.QueryString;

if (n.HasKeys())
 {
 //something
 }
</code></pre>

Return Value
Type: System.Boolean
true if the NameValueCollection contains keys that are not null; otherwise, false. <a href="https://msdn.microsoft.com/en-us/library/system.collections.specialized.namevaluecollection.haskeys(v=vs.110).aspx" rel="nofollow noreferrer">LINK</a>

blocks|key|397419|text|当我在small+elements集合中工作时，我正在使用这个集合。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|397420|在元素较多的地方，我认为需要使用“字典”。我的代码：|397421|NameValueCollection+ProdIdes;
string+prodId+=+_cfg.ProdIdes[key];
if+(string.IsNullOrEmpty(prodId))
{
++++......
}|code-block|syntax|javascript|397422|或者可以使用以下命令：|397423|+string+prodId+=+_cfg.ProdIdes[key]+!=null+?+"found"+:+"not+found";|397424|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|P|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|Q|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|S|8|@]|9|@]|A|$G|H]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

I am using this collection, when I worked in small elements collection.

Where elements lot, I think need use "Dictionary".
My code:

<pre><code>NameValueCollection ProdIdes;
string prodId = _cfg.ProdIdes[key];
if (string.IsNullOrEmpty(prodId))
{
 ......
}
</code></pre>

Or may be use this:

<pre><code> string prodId = _cfg.ProdIdes[key] !=null ? "found" : "not found";
</code></pre>

blocks|key|613512|text|queryItems.AllKeys.Contains(key)|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|613513|请注意，键可能不是唯一的，并且比较通常区分大小写。如果您只想获取第一个匹配键的值，而不需要考虑大小写，那么可以使用以下命令：|unstyled|613514|++++++++public+string+GetQueryValue(string+queryKey)
++++++++{
++++++++++++foreach+(string+key+in+QueryItems)
++++++++++++{
++++++++++++++++if(queryKey.Equals(key,+StringComparison.OrdinalIgnoreCase))
++++++++++++++++++++return+QueryItems.GetValues(key).First();+//+There+might+be+multiple+keys+of+the+same+name,+but+just+return+the+first+match
++++++++++++}
++++++++++++return+null;
++++++++}|613515|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|L|8|@]|9|@]|A|$]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$B|C]]|$1|I|3|-4|5|F|7|N|8|@]|9|@]|A|$]]]|J|$]]

<pre><code>queryItems.AllKeys.Contains(key)
</code></pre>

Be aware that key may not be unique and that the comparison is usually case sensitive. If you want to just get the value of the first matching key and not bothered about case then use this:

<pre><code> public string GetQueryValue(string queryKey)
 {
 foreach (string key in QueryItems)
 {
 if(queryKey.Equals(key, StringComparison.OrdinalIgnoreCase))
 return QueryItems.GetValues(key).First(); // There might be multiple keys of the same name, but just return the first match
 }
 return null;
 }
</code></pre>

Is there a quick and simple way to check if a key exists in a NameValueCollection without looping through it?

Looking for something like Dictionary.ContainsKey() or similar.

There are many ways to solve this of course. Just wondering if someone can help scratch my brain itch.

Check if Key Exists in NameValueCollection

有没有一种快速而简单的方法来检查一个键是否存在于NameValueCollection中，而不是遍历它？寻找类似于Dictionary.ContainsKey()或类似的东西。当然，有很多方法可以解决这个问题。只是想知道有没有人能帮我挠挠我的脑部。

问检查NameValueCollection中是否存在密钥
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