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C# NameValueCollection UsageUse the NameValueCollection type and benchmark its lookup performance.
NameValueCollection allows many values for one key. It is found in System.Collections.Specialized. It does not provide excellent performance. Other collections are likely to be faster for your program.
First, we create a new NameValueCollection. We then adds four string key-value pairs to it. The keys can occur more than once, but map to the same array of values. You can have one key pointing to two values.
String Literal
GetCollection This returns a new NameValueCollection. The collection maps two names (Sam, Bill) to four values.
So In other words, two keys are mapped to two string arrays. The NameValueCollection always acts on strings.
Array
Also The NameValueCollection defines an AllKeys property. We use it in a foreach-loop to see all the keys in the collection.
Property
Foreach
Get value. Here we get a value in the collection using a string key. This is how you can use AppSettings in ASP.NET, or the QueryString collection. The collection returns null as a value if the key is not found.
And If more than one value is found, the string returned contains the values joined by commas.
C# program that uses NameValueCollection
using System; using System.Collections.Specialized; class Program { static NameValueCollection GetCollection() { NameValueCollection collection = new NameValueCollection(); collection.Add("Sam", "Dot Net Perls"); collection.Add("Bill", "Microsoft"); collection.Add("Bill", "White House"); collection.Add("Sam", "IBM"); return collection; } static void Main() { NameValueCollection collection = GetCollection(); foreach (string key in collection.AllKeys) // <-- No duplicates returned. { Console.WriteLine(key); } } }
Sam Bill
Get methods. Here we see that the NameValueCollection also allows you to test whether there are keys, with HasKeys. It also lets you use GetKey with an index to get the key at that index. You can use Get to get the value at that index.
Note My research has shown that the fastest way of accessing values in small NameValueCollections is with these methods.
C# program that uses NameValueCollection indexer
using System; using System.Collections.Specialized; class Program { static void Main() { NameValueCollection collection = GetCollection(); Console.WriteLine(collection["Sam"]); // <-- Same as GetValues Console.WriteLine(collection["X"] == null); // <-- Not found } }
Dot Net Perls,IBM True
Remove value. You can also remove a key-value pair using the Remove method on NameValueCollection. This method requires that you pass it a string key for the pair. I found that you can remove a nonexistent value without throwing an exception.
Also If you remove a key of NameValueCollection, all its values are also removed.
C# program that uses Get
using System; using System.Collections.Specialized; class Program { static void Main() { NameValueCollection collection = GetCollection(); // <-- See first example // Write whether the collection has keys. Console.WriteLine(collection.HasKeys()); // Write the first key. Console.WriteLine(collection.GetKey(0)); // Get the first value. string value = collection.Get(0); Console.WriteLine(value); } }
True Sam Dot Net Perls,IBM
Count pairs. You can count all the key-value pairs in the NameValueCollection. With the Count property, all the duplicate keys are considered separated. Each pair, even if it has the same key as another, is counted separately.
Note To test this, add multiple identical keys, and then check the Count. Duplicates add to the result of Count.
NameValueCollection tested
var collection = new NameValueCollection(); collection.Add("Sam", "Dot Net Perls"); collection.Add("Bill", "Microsoft"); collection.Add("Steve", "Apple"); collection.Add("Rupert", "News Corporation");
var dictionary = new Dictionary<string, string>(); dictionary.Add("Sam", "Dot Net Perls"); dictionary.Add("Bill", "Microsoft"); dictionary.Add("Steve", "Apple"); dictionary.Add("Rupert", "News Corporation");
string value = collection["Steve"];
string value = dictionary["Steve"];
NameValueCollection lookup: 2768 ms Dictionary lookup: 407 ms [faster]
ASP.NET. The NameValueCollection is prevalent in ASP.NET, and it is used in appSettings, QueryString, and Headers collections. First, it is used in appSettings, which allows you to retrieve settings from your Web.config file.
appSettings
QueryString usage. The NameValueCollection is also used in the query string collection in ASP.NET. You can access the query values very quickly simply by specifying the string key. This may not be optimal.
QueryString
Benchmark. Here we see sample code that was benchmarked. To reproduce the benchmark, you will need to paste the code blocks into a test harness and compile in Release mode outside of the debugger.
Result The NameValueCollection's lookup speed on even a small collection was poor. Its performance is likely much worse in many situations.
Therefore The collection must be tested before being used in performance-critical code.
Summary. We used NameValueCollection in the C# language. The collection is located in the System.Collections.Specialized namespace. It allows you to associate one string key with multiple string values.
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