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generic <typename TKey, typename TValue>
public interface class IDictionary : System::Collections::Generic::ICollection<System::Collections::Generic::KeyValuePair<TKey, TValue>>, System::Collections::Generic::IEnumerable<System::Collections::Generic::KeyValuePair<TKey, TValue>>
public interface IDictionary<TKey,TValue> : System.Collections.Generic.ICollection<System.Collections.Generic.KeyValuePair<TKey,TValue>>, System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<TKey,TValue>>
type IDictionary<'Key, 'Value> = interface
interface ICollection<KeyValuePair<'Key, 'Value>>
interface seq<KeyValuePair<'Key, 'Value>>
interface IEnumerable
Public Interface IDictionary(Of TKey, TValue)
Implements ICollection(Of KeyValuePair(Of TKey, TValue)), IEnumerable(Of KeyValuePair(Of TKey, TValue))
Type Parameters
Examples
The following code example creates an empty
Dictionary<TKey,TValue>
of strings, with string keys, and accesses it through the
IDictionary<TKey,TValue>
interface.
The code example uses the
Add
method to add some elements. The example demonstrates that the
Add
method throws
ArgumentException
when attempting to add a duplicate key.
The example uses the
Item[]
property (the indexer in C#) to retrieve values, demonstrating that a
KeyNotFoundException
is thrown when a requested key is not present, and showing that the value associated with a key can be replaced.
The example shows how to use the
TryGetValue
method as a more efficient way to retrieve values if a program often must try key values that are not in the dictionary, and how to use the
ContainsKey
method to test whether a key exists prior to calling the
Add
method.
Finally, the example shows how to enumerate the keys and values in the dictionary, and how to enumerate the values alone using the
Values
property.
using namespace System;
using namespace System::Collections::Generic;
public ref class Example
public:
static void Main()
// Create a new dictionary of strings, with string keys,
// and access it through the IDictionary generic interface.
IDictionary<String^, String^>^ openWith =
gcnew Dictionary<String^, String^>();
// Add some elements to the dictionary. There are no
// duplicate keys, but some of the values are duplicates.
openWith->Add("txt", "notepad.exe");
openWith->Add("bmp", "paint.exe");
openWith->Add("dib", "paint.exe");
openWith->Add("rtf", "wordpad.exe");
// The Add method throws an exception if the new key is
// already in the dictionary.
openWith->Add("txt", "winword.exe");
catch (ArgumentException^)
Console::WriteLine("An element with Key = \"txt\" already exists.");
// The Item property is another name for the indexer, so you
// can omit its name when accessing elements.
Console::WriteLine("For key = \"rtf\", value = {0}.",
openWith["rtf"]);
// The indexer can be used to change the value associated
// with a key.
openWith["rtf"] = "winword.exe";
Console::WriteLine("For key = \"rtf\", value = {0}.",
openWith["rtf"]);
// If a key does not exist, setting the indexer for that key
// adds a new key/value pair.
openWith["doc"] = "winword.exe";
// The indexer throws an exception if the requested key is
// not in the dictionary.
Console::WriteLine("For key = \"tif\", value = {0}.",
openWith["tif"]);
catch (KeyNotFoundException^)
Console::WriteLine("Key = \"tif\" is not found.");
// When a program often has to try keys that turn out not to
// be in the dictionary, TryGetValue can be a more efficient
// way to retrieve values.
String^ value = "";
if (openWith->TryGetValue("tif", value))
Console::WriteLine("For key = \"tif\", value = {0}.", value);
Console::WriteLine("Key = \"tif\" is not found.");
// ContainsKey can be used to test keys before inserting
// them.
if (!openWith->ContainsKey("ht"))
openWith->Add("ht", "hypertrm.exe");
Console::WriteLine("Value added for key = \"ht\": {0}",
openWith["ht"]);
// When you use foreach to enumerate dictionary elements,
// the elements are retrieved as KeyValuePair objects.
Console::WriteLine();
for each( KeyValuePair<String^, String^> kvp in openWith )
Console::WriteLine("Key = {0}, Value = {1}",
kvp.Key, kvp.Value);
// To get the values alone, use the Values property.
ICollection<String^>^ icoll = openWith->Values;
// The elements of the ValueCollection are strongly typed
// with the type that was specified for dictionary values.
Console::WriteLine();
for each( String^ s in icoll )
Console::WriteLine("Value = {0}", s);
// To get the keys alone, use the Keys property.
icoll = openWith->Keys;
// The elements of the ValueCollection are strongly typed
// with the type that was specified for dictionary values.
Console::WriteLine();
for each( String^ s in icoll )
Console::WriteLine("Key = {0}", s);
// Use the Remove method to remove a key/value pair.
Console::WriteLine("\nRemove(\"doc\")");
openWith->Remove("doc");
if (!openWith->ContainsKey("doc"))
Console::WriteLine("Key \"doc\" is not found.");
int main()
Example::Main();
/* This code example produces the following output:
An element with Key = "txt" already exists.
For key = "rtf", value = wordpad.exe.
For key = "rtf", value = winword.exe.
Key = "tif" is not found.
Key = "tif" is not found.
Value added for key = "ht": hypertrm.exe
Key = txt, Value = notepad.exe
Key = bmp, Value = paint.exe
Key = dib, Value = paint.exe
Key = rtf, Value = winword.exe
Key = doc, Value = winword.exe
Key = ht, Value = hypertrm.exe
Value = notepad.exe
Value = paint.exe
Value = paint.exe
Value = winword.exe
Value = winword.exe
Value = hypertrm.exe
Key = txt
Key = bmp
Key = dib
Key = rtf
Key = doc
Key = ht
Remove("doc")
Key "doc" is not found.
using System;
using System.Collections.Generic;
public class Example
public static void Main()
// Create a new dictionary of strings, with string keys,
// and access it through the IDictionary generic interface.
IDictionary<string, string> openWith =
new Dictionary<string, string>();
// Add some elements to the dictionary. There are no
// duplicate keys, but some of the values are duplicates.
openWith.Add("txt", "notepad.exe");
openWith.Add("bmp", "paint.exe");
openWith.Add("dib", "paint.exe");
openWith.Add("rtf", "wordpad.exe");
// The Add method throws an exception if the new key is
// already in the dictionary.
openWith.Add("txt", "winword.exe");
catch (ArgumentException)
Console.WriteLine("An element with Key = \"txt\" already exists.");
// The Item property is another name for the indexer, so you
// can omit its name when accessing elements.
Console.WriteLine("For key = \"rtf\", value = {0}.",
openWith["rtf"]);
// The indexer can be used to change the value associated
// with a key.
openWith["rtf"] = "winword.exe";
Console.WriteLine("For key = \"rtf\", value = {0}.",
openWith["rtf"]);
// If a key does not exist, setting the indexer for that key
// adds a new key/value pair.
openWith["doc"] = "winword.exe";
// The indexer throws an exception if the requested key is
// not in the dictionary.
Console.WriteLine("For key = \"tif\", value = {0}.",
openWith["tif"]);
catch (KeyNotFoundException)
Console.WriteLine("Key = \"tif\" is not found.");
// When a program often has to try keys that turn out not to
// be in the dictionary, TryGetValue can be a more efficient
// way to retrieve values.
string value = "";
if (openWith.TryGetValue("tif", out value))
Console.WriteLine("For key = \"tif\", value = {0}.", value);
Console.WriteLine("Key = \"tif\" is not found.");
// ContainsKey can be used to test keys before inserting
// them.
if (!openWith.ContainsKey("ht"))
openWith.Add("ht", "hypertrm.exe");
Console.WriteLine("Value added for key = \"ht\": {0}",
openWith["ht"]);
// When you use foreach to enumerate dictionary elements,
// the elements are retrieved as KeyValuePair objects.
Console.WriteLine();
foreach( KeyValuePair<string, string> kvp in openWith )
Console.WriteLine("Key = {0}, Value = {1}",
kvp.Key, kvp.Value);
// To get the values alone, use the Values property.
ICollection<string> icoll = openWith.Values;
// The elements of the ValueCollection are strongly typed
// with the type that was specified for dictionary values.
Console.WriteLine();
foreach( string s in icoll )
Console.WriteLine("Value = {0}", s);
// To get the keys alone, use the Keys property.
icoll = openWith.Keys;
// The elements of the ValueCollection are strongly typed
// with the type that was specified for dictionary values.
Console.WriteLine();
foreach( string s in icoll )
Console.WriteLine("Key = {0}", s);
// Use the Remove method to remove a key/value pair.
Console.WriteLine("\nRemove(\"doc\")");
openWith.Remove("doc");
if (!openWith.ContainsKey("doc"))
Console.WriteLine("Key \"doc\" is not found.");
/* This code example produces the following output:
An element with Key = "txt" already exists.
For key = "rtf", value = wordpad.exe.
For key = "rtf", value = winword.exe.
Key = "tif" is not found.
Key = "tif" is not found.
Value added for key = "ht": hypertrm.exe
Key = txt, Value = notepad.exe
Key = bmp, Value = paint.exe
Key = dib, Value = paint.exe
Key = rtf, Value = winword.exe
Key = doc, Value = winword.exe
Key = ht, Value = hypertrm.exe
Value = notepad.exe
Value = paint.exe
Value = paint.exe
Value = winword.exe
Value = winword.exe
Value = hypertrm.exe
Key = txt
Key = bmp
Key = dib
Key = rtf
Key = doc
Key = ht
Remove("doc")
Key "doc" is not found.
Imports System.Collections.Generic
Public Class Example
Public Shared Sub Main()
' Create a new dictionary of strings, with string keys,
' and access it through the IDictionary generic interface.
Dim openWith As IDictionary(Of String, String) = _
New Dictionary(Of String, String)
' Add some elements to the dictionary. There are no
' duplicate keys, but some of the values are duplicates.
openWith.Add("txt", "notepad.exe")
openWith.Add("bmp", "paint.exe")
openWith.Add("dib", "paint.exe")
openWith.Add("rtf", "wordpad.exe")
' The Add method throws an exception if the new key is
' already in the dictionary.
openWith.Add("txt", "winword.exe")
Catch
Console.WriteLine("An element with Key = ""txt"" already exists.")
End Try
' The Item property is the default property, so you
' can omit its name when accessing elements.
Console.WriteLine("For key = ""rtf"", value = {0}.", _
openWith("rtf"))
' The default Item property can be used to change the value
' associated with a key.
openWith("rtf") = "winword.exe"
Console.WriteLine("For key = ""rtf"", value = {0}.", _
openWith("rtf"))
' If a key does not exist, setting the default item property
' for that key adds a new key/value pair.
openWith("doc") = "winword.exe"
' The default Item property throws an exception if the requested
' key is not in the dictionary.
Console.WriteLine("For key = ""tif"", value = {0}.", _
openWith("tif"))
Catch
Console.WriteLine("Key = ""tif"" is not found.")
End Try
' When a program often has to try keys that turn out not to
' be in the dictionary, TryGetValue can be a more efficient
' way to retrieve values.
Dim value As String = ""
If openWith.TryGetValue("tif", value) Then
Console.WriteLine("For key = ""tif"", value = {0}.", value)
Console.WriteLine("Key = ""tif"" is not found.")
End If
' ContainsKey can be used to test keys before inserting
' them.
If Not openWith.ContainsKey("ht") Then
openWith.Add("ht", "hypertrm.exe")
Console.WriteLine("Value added for key = ""ht"": {0}", _
openWith("ht"))
End If
' When you use foreach to enumerate dictionary elements,
' the elements are retrieved as KeyValuePair objects.
Console.WriteLine()
For Each kvp As KeyValuePair(Of String, String) In openWith
Console.WriteLine("Key = {0}, Value = {1}", _
kvp.Key, kvp.Value)
Next kvp
' To get the values alone, use the Values property.
Dim icoll As ICollection(Of String) = openWith.Values
' The elements of the ValueCollection are strongly typed
' with the type that was specified for dictionary values.
Console.WriteLine()
For Each s As String In icoll
Console.WriteLine("Value = {0}", s)
Next s
' To get the keys alone, use the Keys property.
icoll = openWith.Keys
' The elements of the ValueCollection are strongly typed
' with the type that was specified for dictionary values.
Console.WriteLine()
For Each s As String In icoll
Console.WriteLine("Key = {0}", s)
Next s
' Use the Remove method to remove a key/value pair.
Console.WriteLine(vbLf + "Remove(""doc"")")
openWith.Remove("doc")
If Not openWith.ContainsKey("doc") Then
Console.WriteLine("Key ""doc"" is not found.")
End If
End Sub
End Class
' This code example produces the following output:
'An element with Key = "txt" already exists.
'For key = "rtf", value = wordpad.exe.
'For key = "rtf", value = winword.exe.
'Key = "tif" is not found.
'Key = "tif" is not found.
'Value added for key = "ht": hypertrm.exe
'Key = txt, Value = notepad.exe
'Key = bmp, Value = paint.exe
'Key = dib, Value = paint.exe
'Key = rtf, Value = winword.exe
'Key = doc, Value = winword.exe
'Key = ht, Value = hypertrm.exe
'Value = notepad.exe
'Value = paint.exe
'Value = paint.exe
'Value = winword.exe
'Value = winword.exe
'Value = hypertrm.exe
'Key = txt
'Key = bmp
'Key = dib
'Key = rtf
'Key = doc
'Key = ht
'Remove("doc")
'Key "doc" is not found.
The
IDictionary<TKey,TValue>
interface is the base interface for generic collections of key/value pairs.
Each element is a key/value pair stored in a
KeyValuePair<TKey,TValue>
object.
Each pair must have a unique key. Implementations can vary in whether they allow
key
to be
null
. The value can be
null
and does not have to be unique. The
IDictionary<TKey,TValue>
interface allows the contained keys and values to be enumerated, but it does not imply any particular sort order.
The
foreach
statement of the C# language (
For Each
in Visual Basic,
for each
in C++) returns an object of the type of the elements in the collection. Since each element of the
IDictionary<TKey,TValue>
is a key/value pair, the element type is not the type of the key or the type of the value. Instead, the element type is
KeyValuePair<TKey,TValue>
. For example:
for each(KeyValuePair<int, String^> kvp in myDictionary)
Console::WriteLine("Key = {0}, Value = {1}", kvp.Key, kvp.Value);
foreach (KeyValuePair<int, string> kvp in myDictionary)
Console.WriteLine("Key = {0}, Value = {1}", kvp.Key, kvp.Value);
For Each kvp As KeyValuePair(Of Integer, String) In myDictionary
Console.WriteLine("Key = {0}, Value = {1}", kvp.Key, kvp.Value)
Next kvp
The
foreach
statement is a wrapper around the enumerator, which only allows reading from, not writing to, the collection.
Because keys can be inherited and their behavior changed, their absolute uniqueness cannot be guaranteed by comparisons using the
Equals
method.
Notes to Implementers
The implementing class must have a means to compare keys.
Copies the elements of the
ICollection<T>
to an
Array
, starting at a particular
Array
index.
(Inherited from
ICollection<T>
)
ToImmutableDictionary<TSource,TKey,TValue>(IEnumerable<TSource>,
Func<TSource,TKey>, Func<TSource,TValue>, IEqualityComparer<TKey>,
IEqualityComparer<TValue>)
Enumerates and transforms a sequence, and produces an immutable dictionary of its contents by using the specified key and value comparers.
GroupBy<TSource,TKey,TElement,TResult>(IEnumerable<TSource>, Func<TSource,
TKey>, Func<TSource,TElement>, Func<TKey,IEnumerable<TElement>,
TResult>, IEqualityComparer<TKey>)
Groups the elements of a sequence according to a specified key selector function and creates a result value from each group and its key. Key values are compared by using a specified comparer, and the elements of each group are projected by using a specified function.
GroupJoin<TOuter,TInner,TKey,TResult>(IEnumerable<TOuter>, IEnumerable<TInner>,
Func<TOuter,TKey>, Func<TInner,TKey>, Func<TOuter,IEnumerable<TInner>,
TResult>)
Correlates the elements of two sequences based on equality of keys and groups the results. The default equality comparer is used to compare keys.
GroupJoin<TOuter,TInner,TKey,TResult>(IEnumerable<TOuter>, IEnumerable<TInner>,
Func<TOuter,TKey>, Func<TInner,TKey>, Func<TOuter,IEnumerable<TInner>,
TResult>, IEqualityComparer<TKey>)
Correlates the elements of two sequences based on key equality and groups the results. A specified
IEqualityComparer<T>
is used to compare keys.
Join<TOuter,TInner,TKey,TResult>(IEnumerable<TOuter>, IEnumerable<TInner>,
Func<TOuter,TKey>, Func<TInner,TKey>, Func<TOuter,TInner,TResult>,
IEqualityComparer<TKey>)
Correlates the elements of two sequences based on matching keys. A specified
IEqualityComparer<T>
is used to compare keys.
