C# Iterate through NameValueCollection

问题:

I have a NameValueCollection, and want to iterate through the values. Currently, I’m doing this, but it seems like there should be a neater way to do it:

NameValueCollection nvc = new NameValueCollection();
nvc.Add("Test", "Val1");
nvc.Add("Test2", "Val1");
nvc.Add("Test2", "Val1");
nvc.Add("Test2", "Val2");
nvc.Add("Test3", "Val1");
nvc.Add("Test4", "Val4");

foreach (string s in nvc)
    foreach (string v in nvc.GetValues(s))
        Console.WriteLine("{0} {1}", s, v);

Console.ReadLine();

Is there?

回答1:

You can flatten the collection with Linq, but it's still a foreach loop but now more implicit.

var items = nvc.AllKeys.SelectMany(nvc.GetValues, (k, v) => new {key = k, value = v});
foreach (var item in items)
    Console.WriteLine("{0} {1}", item.key, item.value);

The first line, converts the nested collection to a (non-nested) collection of anonymous objects with the properties key and value.

It's flatten in the way that it's now a mapping key -> value instead of key -> collection of values. The example data:

Before:

Test -> [Val],

Test2 -> [Val1, Val1, Val2],

Test3 -> [Val1],

Test4 -> [Val4]

After:

Test -> Val,

Test2 -> Val1,

Test2 -> Val1,

Test2 -> Val2,

Test3 -> Val1,

Test4 -> Val4

回答2:

You can use the key for lookup instead of having two loops:

foreach (string key in nvc)
{
    Console.WriteLine("{0} {1}", key, nvc[key]);
}

回答3:

Nothing new to see here (@Julian's +1'd by me answer is functionally equivalent), y'all move along y'all please.

---

I have an [overkill for this case but possibly relevant] set of extension methods in an answer to a related question, which would let you do:

foreach ( KeyValuePair<string,string> item in nvc.AsEnumerable().AsKeyValuePairs() )
    Console.WriteLine("{0} {1}", item.key, item.value);

回答4:

The only way I found to avoid the nested loops is using additional List to store the values:

List<string> arrValues = new List<string>();
for (int i = 0; i < nvc.Count; i++)
    arrValues.AddRange(nvc.GetValues(i));
foreach (string value in arrValues)
    Console.WriteLine(value);

(Requires [only] .NET 2.0 or later)

回答5:

I think this is simpler:

For i As Integer = 0 To nvc.Count - 1
   Console.Write("No", "Key", "Value")
   Console.Write(i, nvc.GetKey(i), nvc.Get(i))
Next

回答6:

foreach ( string key in nvc.Keys )
   Console.WriteLine("{0} {1}", key, nvc[key]);

This will return you all keys and corresponding values.