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.
We use it in a foreach-loop to see all the keys in the collection. NameValueCollection allows many values for one key. It is found in System.
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. Property Foreach. Add "Sam", "Dot Net Perls" ; collection. Add "Bill", "Microsoft" ; collection. Add "Bill", "White House" ; collection. Get value. Here we get a value in the collection using a string key. 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. 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.Part 1: Here we initialize a List of pairs. Each pair has 2 types separated by a comma string, int.
Part 2: KeyValuePairs are immutable, so we cannot change them after they are created, but we can print them. Var: For simpler and shorter syntax, we can use the var keyword with the foreach-loop over the Dictionary.
Tip: For descending, we take the second argument, and compare it to the first instead of the other way around. C program that uses lambda, sorts KeyValuePairs using System.
Use reverse order of A and B to mean descending sort. CompareTo a. Here is the basic layout of the KeyValuePair struct. The KeyValuePair has 2 private fields, and 2 public properties that retrieve the values of those fields. Write or Console. This will implicitly call ToString. This may cause memory pressure. Avoiding ToString can speed up programs. C program that uses ToString using System; using System.
ToString ; Console. KeyValuePair wastes no memory. It is compact. Consider this example program: it has 2 versions of code, each of which store keys and values. Version 1: The keys and values are stored in 2 separate arrays. The GC. GetTotalMemory method measures the memory usage. Version 2: This version uses a single array of KeyValuePair structs. Again, the GC. GetTotalMemory method is used. Result: The version that uses 1 array of KeyValuePairs uses a few bytes less of memory.
So KeyValuePair wastes no space. Tip: Performance may be affected by the KeyValuePair version, as we must access properties rather than array elements. Collect ; Console. Is there any advantage to using custom structs instead of KeyValuePair generic types? The 2 approaches are equivalent in functionality. Next: We look at a benchmark that compares 2 structs. It seems logical the methods should have the same performance. Version 1: This code calls a method that receives a CustomPair struct instance.
Version 2: This code calls a method overload that receives a KeyValuePair struct method overloading selects the correct method.
C# NameValueCollection Usage
Result: It is possible to improve performance by replacing a KeyValuePair with a regular struct. The behavior of the inliner is sometimes hard to determine. Sort, no lambdas. How can we sort a collection of KeyValuePair instances?NameValueCollection implements IEnumerablewhich is different. Try OfType it accepts the non-generic interface.
A dictionary is probably actually closer to what you want to use since it will actually fill more of the roles that NameValueCollection fills.
This is a variation of Bryan Watts' solution:. I don't really see why anyone would need to add an extension method. Here's some different ways to do it in VB. For the C equivalent go to converter. I know I'm late to the party but just wanted to add my answer that doesn't involve the. Cast extension method but instead uses the AllKeys property:. It has been suggested that you use OfType but that is a filtering method.
What you're doing is the equivalent of a cast, for which there is the Cast operator:. As Frans pointed out, this only provides access to the keys.
How to convert NameValueCollection to a (Query) String
You would still need to index into the collection for the values. Edit: In response to Ruben Bartelink's request, here is how to access the full set of values for each key using ToLookup :.
Cast Of String. Cast Of Object. Cast Of String Select Tuple. ToDictionary Function tuple tuple. Item1, Function tuple tuple. ToDictionary Function anon anon. X, Function anon anon. ToDictionary Function kvp kvp. Key, Function kvp kvp. First and when to use.NameValueCollection is used to store a collection of associated String keys and String values that can be accessed either with the key or with the index.
NameValueCollection can hold multiple string values under a single key. As elements are added to a NameValueCollection, the capacity is automatically increased as required through reallocation. The one important thing is that you have to import System. Specialized Class in your program for using NameValueCollection. Home C VB.
How to use C NameValueCollection Class NameValueCollection is used to store a collection of associated String keys and String values that can be accessed either with the key or with the index.
Adding new pairs NameValueCollection. Download Source Code. Print Source Code. Collections; using System. Forms; using System. Add "Very High", "80" ; markStatus. Add "High", "60" ; markStatus. Add "medium", "50" ; markStatus. Add "Pass", "40" ; foreach string key in markStatus. Byte Array to a text file String Array to a text file. All other trademarks are property of their respective owners.Represents a collection of associated String keys and String values that can be accessed either with the key or with the index.
This collection is based on the NameObjectCollectionBase class. However, unlike the NameObjectCollectionBasethis class can store multiple string values under a single key.
Collections of this type do not preserve the ordering of elements, and no particular ordering is guaranteed when enumerating the collection. As elements are added, its capacity is automatically increased as required through reallocation. The hash code provider dispenses hash codes for keys in the NameValueCollection. The comparer determines whether two keys are equal.
The default comparer is a CaseInsensitiveComparer that uses the conventions of the invariant culture ; that is, key comparisons are case-insensitive by default.06 key value pair connection string
To perform case-sensitive key comparisons, call the NameValueCollection. CurrentCultureStringComparer. InvariantCultureor StringComparer. Ordinal as the equalityComparer argument. For more information about how culture affects comparisons and sorting, see Performing Culture-Insensitive String Operations.
The Get method does not distinguish between null which is returned because the specified key is not found and null which is returned because the value associated with the key is null.
Initializes a new instance of the NameValueCollection class that is empty, has the default initial capacity and uses the default case-insensitive hash code provider and the default case-insensitive comparer. Initializes a new instance of the NameValueCollection class that is empty, has the default initial capacity, and uses the specified IEqualityComparer object. Initializes a new instance of the NameValueCollection class that is empty, has the default initial capacity and uses the specified hash code provider and the specified comparer.
Initializes a new instance of the NameValueCollection class that is empty, has the specified initial capacity and uses the default case-insensitive hash code provider and the default case-insensitive comparer. Initializes a new instance of the NameValueCollection class that is empty, has the specified initial capacity, and uses the specified IEqualityComparer object. Initializes a new instance of the NameValueCollection class that is empty, has the specified initial capacity and uses the specified hash code provider and the specified comparer.
The dark mode beta is finally here. Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. Why is this? Also, foreach only exposes the key:. Note: inspired by this. SelectMany is required to handle duplicate keys. Be aware that the key name might appear more than once in the query string 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:.
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C# NameValueCollection Usage
I like this as I can init a dictionary without having to create a backing dictionary variable in addition to a foreach. ParseQueryString Request. Active Oldest Votes. Hmm, that's kind of weird. I would have expected there to be a way to get both at once.If I wish to submit a http get request using System. HttpClient there seems to be no api to add parameters, is this correct? Is there any simple api available to build the query string that doesn't involve building a name value collection and url encoding those and then finally concatenating them?
I was hoping to use something like RestSharp's api i. So, If you're dealing with characters which need to be encoded, accepted solution leads to double encoding:. As you may see, no matter if you do uribuilder. GetStringAsync string or uriBuilder. GetStringAsync Uri you end up sending double encoded parameter. S on my latest. NET on Windows Server, Uri constructor with bool doc comment says "obsolete, dontEscape is always false", but actually works as expected skips escaping. And even this is plain wrong - it send UrlEncodedUnicode to server, not just UrlEncoded what server expects.
Update: one more thing is, NameValueCollection actually does UrlEncodeUnicode, which is not supposed to be used anymore and is incompatible with regular url. ParseQueryString builder. Query ; as it will mess your unicode query parameters. Just build query manually and assign it to UriBuilder. Query which will do necessary encoding and then get Uri using UriBuilder.
For those who do not want to include System. Http and do something like the following:. Good part of accepted answer, modified to use UriBuilder. ParseQueryString instead of HttpUtility. ParseQueryString :. All encoding is handled for you in accordance with that RFC.
At the time of this writing, a beta release is available and the only reason it's not considered a stable 1. To avoid double encoding issue described in taras. You can always use IEnterprise. Easy-HTTP because it has a built in query builder:.
Build query string for System. HttpClient get 10 If I wish to submit a http get request using System. ParseQueryString string.