foreach KeyValuePair in NameValueCollection?

NameValueCollection nv = HttpUtility.ParseQueryString(queryString);        
foreach (KeyValuePair<String,String> pr in nv) {
    //process KeyValuePair          
}

首先，NameValueCollection不使用KeyValuePair<String,String>。同样，foreach只公开键:

NameValueCollection nv = HttpUtility.ParseQueryString(queryString);        
foreach (string key in nv) {
    var value = nv[key];
}

您不能直接这样做，但是您可以创建一个扩展方法，像这样:

public static IEnumerable<KeyValuePair<string, string>> AsKVP(
        this NameValueCollection source
)
{
    return source.AllKeys.SelectMany(
        source.GetValues,
        (k, v) => new KeyValuePair<string, string>(k, v));
}

那么你可以这样做:

NameValueCollection nv = HttpUtility.ParseQueryString(queryString);
foreach (KeyValuePair<String,String> pr in nv.AsKVP()) {
    //process KeyValuePair          
}

注意:受此启发。需要SelectMany来处理重复的键。

vb.net版本:

<Extension>
Public Function AsKVP(
        source As Specialized.NameValueCollection
) As IEnumerable(Of KeyValuePair(Of String, String))
    Dim result = source.AllKeys.SelectMany(
        AddressOf source.GetValues,
        Function(k, v) New KeyValuePair(Of String, String)(k, v))
    Return result
End Function

对于将来的参考，您还可以使用以下语法:

foreach(string key in Request.QueryString)
{
    var value = Request.QueryString[key];
}

另一个扩展方法，用于学习:

    public static IEnumerable<KeyValuePair<string, string>> ToIEnumerable(this NameValueCollection nvc)
    {
        foreach (string key in nvc.AllKeys)
        {
            yield return new KeyValuePair<string, string>(key, nvc[key]);
        }
    }

NameValueCollection使用老式的枚举器:

        var enu = ConfigurationManager.AppSettings.GetEnumerator();
        while(enu.MoveNext())
        {
            string key = (string)enu.Current;
            string value = ConfigurationManager.AppSettings[key];
        }

我这样做了，它工作了:

 foreach (string akey in request.Query.Keys.Cast<string>())
     writer.WriteLine(akey + " = " + request.Query[akey]);

请注意，键名可能在查询字符串中出现多次，并且比较通常是区分大小写的。
如果你只想获得第一个匹配键的值，而不需要考虑大小写，那么使用这个:

        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;
        }

要将nameValueCollection从QueryString转换为List，可以使用如下扩展:

public static List<KeyValuePair<string, string>> GetParams(this HttpRequest request)
{
    var nameValueCollection = HttpUtility.ParseQueryString(request.QueryString.Value);
    List<KeyValuePair<string, string>> keyValueCollections = new List<KeyValuePair<string, string>>();
    if (!nameValueCollection.IsNullOrEmpty())
    {
        foreach (var key in nameValueCollection.AllKeys)
        {
            keyValueCollections.Add(new KeyValuePair<string, string>(key, nameValueCollection[key]));
        }
    }
    return keyValueCollections;
}

如何使用内置的.AsEnumerable()扩展方法?例子:

NameValueCollection nv = HttpUtility.ParseQueryString(queryString);        
foreach (KeyValuePair<String,String> pr in nv.AsEnumerable()) {
    //process KeyValuePair          
}

public static void PrintKeysAndValues2( NameValueCollection myCol )
{
    Console.WriteLine( "   [INDEX] KEY        VALUE" );
    for ( int i = 0; i < myCol.Count; i++ )
        Console.WriteLine( "   [{0}]     {1,-10} {2}", i, myCol.GetKey(i), myCol.Get(i) );
    Console.WriteLine();
}

http://msdn.microsoft.com/en-us/library/system.collections.specialized.namevaluecollection.aspx