Dictionary<TKey,TValue>.ContainsKey(TKey) Méthode

Définition

Espace de noms:

System.Collections.Generic

Assembly:

System.Collections.dll

Source:

Dictionary.cs

Détermine si Dictionary<TKey,TValue> contient la clé spécifiée.

public:
 virtual bool ContainsKey(TKey key);

public bool ContainsKey (TKey key);

abstract member ContainsKey : 'Key -> bool
override this.ContainsKey : 'Key -> bool

Public Function ContainsKey (key As TKey) As Boolean

Paramètres

key

TKey

Clé à rechercher dans Dictionary<TKey,TValue>.

Retours

Boolean

true si Dictionary<TKey,TValue> contient un élément correspondant à la clé spécifiée ; sinon, false.

Implémente

ContainsKey(TKey) ContainsKey(TKey)

Exceptions

ArgumentNullException

key a la valeur null.

Exemples

L’exemple de code suivant montre comment utiliser la ContainsKey méthode pour tester si une clé existe avant d’appeler la Add méthode. Il montre également comment utiliser la méthode pour récupérer des TryGetValue valeurs, qui est un moyen efficace de récupérer des valeurs lorsqu’un programme essaie fréquemment des clés qui ne se trouvent pas dans le dictionnaire. Enfin, il montre le moyen le moins efficace de tester si des clés existent, en utilisant la Item[] propriété (l’indexeur en C#).

Cet exemple de code fait partie d’un exemple plus grand fourni pour la Dictionary<TKey,TValue> classe (openWith est le nom du dictionnaire utilisé dans cet exemple).

// 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"]);
}

// 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"]);
}

' 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 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);
}
else
{
    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);
}
else
{
    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.
Dim value As String = ""
If openWith.TryGetValue("tif", value) Then
    Console.WriteLine("For key = ""tif"", value = {0}.", value)
Else
    Console.WriteLine("Key = ""tif"" is not found.")
End If

// The indexer throws an exception if the requested key is
// not in the dictionary.
try
{
    Console::WriteLine("For key = \"tif\", value = {0}.",
        openWith["tif"]);
}
catch (KeyNotFoundException^)
{
    Console::WriteLine("Key = \"tif\" is not found.");
}

// The indexer throws an exception if the requested key is
// not in the dictionary.
try
{
    Console.WriteLine("For key = \"tif\", value = {0}.",
        openWith["tif"]);
}
catch (KeyNotFoundException)
{
    Console.WriteLine("Key = \"tif\" is not found.");
}

' The default Item property throws an exception if the requested
' key is not in the dictionary.
Try
    Console.WriteLine("For key = ""tif"", value = {0}.", _
        openWith("tif"))
Catch 
    Console.WriteLine("Key = ""tif"" is not found.")
End Try

Remarques

Cette méthode approche une opération O(1).

Voir aussi

• ContainsValue(TValue)