StringDictionary.Item[String] Propriété

Référence

Définition

Espace de noms:: System.Collections.Specialized

Assemblys:: System.dll, System.Collections.Specialized.dll

Assembly:: System.Collections.Specialized.dll

Assembly:: System.dll

Assembly:: netstandard.dll

Source:: StringDictionary.cs

Source:: StringDictionary.cs

Source:: StringDictionary.cs

Important

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Obtient ou définit la valeur associée à la clé spécifiée.

public:
 virtual property System::String ^ default[System::String ^] { System::String ^ get(System::String ^ key); void set(System::String ^ key, System::String ^ value); };

public virtual string this[string key] { get; set; }

public virtual string? this[string key] { get; set; }

member this.Item(string) : string with get, set

Default Public Overridable Property Item(key As String) As String

Paramètres

key: String

Clé dont la valeur doit être obtenue ou définie.

Valeur de propriété

String

Valeur associée à la clé spécifiée. Si la clé spécifiée est introuvable, Get retourne null et Set crée une nouvelle entrée avec la clé spécifiée.

Exceptions

ArgumentNullException

key a la valeur null.

Exemples

L’exemple de code suivant énumère les éléments d’un StringDictionary.

#using <System.dll>

using namespace System;
using namespace System::Collections;
using namespace System::Collections::Specialized;

void PrintKeysAndValues1( StringDictionary^ myCol );
void PrintKeysAndValues2( StringDictionary^ myCol );
void PrintKeysAndValues3( StringDictionary^ myCol );

int main()
{
   // Creates and initializes a new StringDictionary.
   StringDictionary^ myCol = gcnew StringDictionary;
   myCol->Add( "red", "rojo" );
   myCol->Add( "green", "verde" );
   myCol->Add( "blue", "azul" );
   
   // Display the contents of the collection using for each. This is the preferred method.
   Console::WriteLine( "Displays the elements using for each:" );
   PrintKeysAndValues1( myCol );

   // Display the contents of the collection using the enumerator.
   Console::WriteLine( "Displays the elements using the IEnumerator:" );
   PrintKeysAndValues2( myCol );
   
   // Display the contents of the collection using the Keys, Values, Count, and Item properties.
   Console::WriteLine( "Displays the elements using the Keys, Values, Count, and Item properties:" );
   PrintKeysAndValues3( myCol );
}

// Uses the for each statement which hides the complexity of the enumerator.
// NOTE: The for each statement is the preferred way of enumerating the contents of a collection.
void PrintKeysAndValues1( StringDictionary^ myCol )  {
   Console::WriteLine( "   KEY                       VALUE" );
   for each ( DictionaryEntry^ de in myCol )
      Console::WriteLine( "   {0,-25} {1}", de->Key, de->Value );
   Console::WriteLine();
}

// Uses the enumerator. 
void PrintKeysAndValues2( StringDictionary^ myCol )
{
   IEnumerator^ myEnumerator = myCol->GetEnumerator();
   DictionaryEntry^ de;
   Console::WriteLine( "   KEY                       VALUE" );
   while ( myEnumerator->MoveNext() )
   {
      de =  (DictionaryEntry^)(myEnumerator->Current);
      Console::WriteLine( "   {0,-25} {1}", de->Key, de->Value );
   }
   Console::WriteLine();
}

// Uses the Keys, Values, Count, and Item properties.
void PrintKeysAndValues3( StringDictionary^ myCol )
{
   array<String^>^myKeys = gcnew array<String^>(myCol->Count);
   myCol->Keys->CopyTo( myKeys, 0 );
   Console::WriteLine( "   INDEX KEY                       VALUE" );
   for ( int i = 0; i < myCol->Count; i++ )
      Console::WriteLine( "   {0,-5} {1,-25} {2}", i, myKeys[ i ], myCol[ myKeys[ i ] ] );
   Console::WriteLine();
}

/*
This code produces the following output.

Displays the elements using for each:
   KEY                       VALUE
   red                       rojo
   blue                      azul
   green                     verde

Displays the elements using the IEnumerator:
   KEY                       VALUE
   red                       rojo
   blue                      azul
   green                     verde

Displays the elements using the Keys, Values, Count, and Item properties:
   INDEX KEY                       VALUE
   0     red                       rojo
   1     blue                      azul
   2     green                     verde

*/

using System;
using System.Collections;
using System.Collections.Specialized;

public class SamplesStringDictionary  {

   public static void Main()  {

      // Creates and initializes a new StringDictionary.
      StringDictionary myCol = new StringDictionary();
      myCol.Add( "red", "rojo" );
      myCol.Add( "green", "verde" );
      myCol.Add( "blue", "azul" );

      // Display the contents of the collection using foreach. This is the preferred method.
      Console.WriteLine( "Displays the elements using foreach:" );
      PrintKeysAndValues1( myCol );

      // Display the contents of the collection using the enumerator.
      Console.WriteLine( "Displays the elements using the IEnumerator:" );
      PrintKeysAndValues2( myCol );

      // Display the contents of the collection using the Keys, Values, Count, and Item properties.
      Console.WriteLine( "Displays the elements using the Keys, Values, Count, and Item properties:" );
      PrintKeysAndValues3( myCol );
   }

   // Uses the foreach statement which hides the complexity of the enumerator.
   // NOTE: The foreach statement is the preferred way of enumerating the contents of a collection.
   public static void PrintKeysAndValues1( StringDictionary myCol )  {
      Console.WriteLine( "   KEY                       VALUE" );
      foreach ( DictionaryEntry de in myCol )
         Console.WriteLine( "   {0,-25} {1}", de.Key, de.Value );
      Console.WriteLine();
   }

   // Uses the enumerator.
   // NOTE: The foreach statement is the preferred way of enumerating the contents of a collection.
   public static void PrintKeysAndValues2( StringDictionary myCol )  {
      IEnumerator myEnumerator = myCol.GetEnumerator();
      DictionaryEntry de;
      Console.WriteLine( "   KEY                       VALUE" );
      while ( myEnumerator.MoveNext() )  {
         de = (DictionaryEntry) myEnumerator.Current;
         Console.WriteLine( "   {0,-25} {1}", de.Key, de.Value );
      }
      Console.WriteLine();
   }

   // Uses the Keys, Values, Count, and Item properties.
   public static void PrintKeysAndValues3( StringDictionary myCol )  {
      String[] myKeys = new String[myCol.Count];
      myCol.Keys.CopyTo( myKeys, 0 );

      Console.WriteLine( "   INDEX KEY                       VALUE" );
      for ( int i = 0; i < myCol.Count; i++ )
         Console.WriteLine( "   {0,-5} {1,-25} {2}", i, myKeys[i], myCol[myKeys[i]] );
      Console.WriteLine();
   }
}

/*
This code produces the following output.

Displays the elements using foreach:
   KEY                       VALUE
   red                       rojo
   blue                      azul
   green                     verde

Displays the elements using the IEnumerator:
   KEY                       VALUE
   red                       rojo
   blue                      azul
   green                     verde

Displays the elements using the Keys, Values, Count, and Item properties:
   INDEX KEY                       VALUE
   0     red                       rojo
   1     blue                      azul
   2     green                     verde

*/

Imports System.Collections
Imports System.Collections.Specialized

Public Class SamplesStringDictionary

   Public Shared Sub Main()

      ' Creates and initializes a new StringDictionary.
      Dim myCol As New StringDictionary()
      myCol.Add("red", "rojo")
      myCol.Add("green", "verde")
      myCol.Add("blue", "azul")

      ' Display the contents of the collection using For Each. This is the preferred method.
      Console.WriteLine("Displays the elements using For Each:")
      PrintKeysAndValues1(myCol)

      ' Display the contents of the collection using the enumerator.
      Console.WriteLine("Displays the elements using the IEnumerator:")
      PrintKeysAndValues2(myCol)

      ' Display the contents of the collection using the Keys, Values, Count, and Item properties.
      Console.WriteLine("Displays the elements using the Keys, Values, Count, and Item properties:")
      PrintKeysAndValues3(myCol)

   End Sub


   ' Uses the For Each statement which hides the complexity of the enumerator.
   ' NOTE: The For Each statement is the preferred way of enumerating the contents of a collection.
   Public Shared Sub PrintKeysAndValues1(myCol As StringDictionary)
      Console.WriteLine("   KEY                       VALUE")
      Dim de As DictionaryEntry
      For Each de In  myCol
         Console.WriteLine("   {0,-25} {1}", de.Key, de.Value)
      Next de
      Console.WriteLine()
   End Sub


   ' Uses the enumerator. 
   ' NOTE: The For Each statement is the preferred way of enumerating the contents of a collection.
   Public Shared Sub PrintKeysAndValues2(myCol As StringDictionary)
      Dim myEnumerator As IEnumerator = myCol.GetEnumerator()
      Dim de As DictionaryEntry
      Console.WriteLine("   KEY                       VALUE")
      While myEnumerator.MoveNext()
         de = CType(myEnumerator.Current, DictionaryEntry)
         Console.WriteLine("   {0,-25} {1}", de.Key, de.Value)
      End While
      Console.WriteLine()
   End Sub


   ' Uses the Keys, Values, Count, and Item properties.
   Public Shared Sub PrintKeysAndValues3(myCol As StringDictionary)
      Dim myKeys(myCol.Count) As String
      myCol.Keys.CopyTo(myKeys, 0)

      Console.WriteLine("   INDEX KEY                       VALUE")
      Dim i As Integer
      For i = 0 To myCol.Count - 1
         Console.WriteLine("   {0,-5} {1,-25} {2}", i, myKeys(i), myCol(myKeys(i)))
      Next i
      Console.WriteLine()
   End Sub

End Class


'This code produces the following output.
'
'Displays the elements using For Each:
'   KEY                       VALUE
'   red                       rojo
'   blue                      azul
'   green                     verde
'
'Displays the elements using the IEnumerator:
'   KEY                       VALUE
'   red                       rojo
'   blue                      azul
'   green                     verde
'
'Displays the elements using the Keys, Values, Count, and Item properties:
'   INDEX KEY                       VALUE
'   0     red                       rojo
'   1     blue                      azul
'   2     green                     verde

Remarques

La clé est gérée de manière non respectant la casse ; il est traduit en minuscules avant d’être utilisé.

Une clé ne peut pas être null, mais une valeur peut. Pour faire la distinction entre null qui est retourné parce que la clé spécifiée est introuvable et null qui est retournée parce que la valeur de la clé spécifiée est null, utilisez la ContainsKey méthode pour déterminer si la clé existe dans la liste.

Le langage C# utilise cette mot clé pour définir les indexeurs au lieu d’implémenter la Item[] propriété. Visual Basic implémente Item[] comme propriété par défaut, ce qui fournit les mêmes fonctionnalités d'indexation.

La récupération de la valeur de cette propriété est une opération O(1) ; la définition de la propriété est également une opération O(1).

S’applique à

Voir aussi

Exécution d'opérations de chaînes indépendantes de la culture