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StringDictionary Class

Implements a hash table with the key and the value strongly typed to be strings rather than objects.

Namespace: System.Collections.Specialized
Assembly: System (in system.dll)

[SerializableAttribute] 
public class StringDictionary : IEnumerable
/** @attribute SerializableAttribute() */ 
public class StringDictionary implements IEnumerable
SerializableAttribute 
public class StringDictionary implements IEnumerable
Not applicable.

A key cannot be a null reference (Nothing in Visual Basic), but a value can.

The key is handled in a case-insensitive manner; it is translated to lowercase before it is used with the string dictionary.

In .NET Framework version 1.0, this class uses culture-sensitive string comparisons. However, in .NET Framework version 1.1 and later, this class uses CultureInfo.InvariantCulture when comparing strings. For more information about how culture affects comparisons and sorting, see Comparing and Sorting Data for a Specific Culture and Performing Culture-Insensitive String Operations.

The following code example demonstrates several of the properties and methods of StringDictionary.

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 );

      // Copies the StringDictionary to an array with DictionaryEntry elements.
      DictionaryEntry[] myArr = new DictionaryEntry[myCol.Count];
      myCol.CopyTo( myArr, 0 );

      // Displays the values in the array.
      Console.WriteLine( "Displays the elements in the array:" );
      Console.WriteLine( "   KEY        VALUE" );
      for ( int i = 0; i < myArr.Length; i++ )
         Console.WriteLine( "   {0,-10} {1}", myArr[i].Key, myArr[i].Value );
      Console.WriteLine();

      // Searches for a value.
      if ( myCol.ContainsValue( "amarillo" ) )
         Console.WriteLine( "The collection contains the value \"amarillo\"." );
      else
         Console.WriteLine( "The collection does not contain the value \"amarillo\"." );
      Console.WriteLine();

      // Searches for a key and deletes it.
      if ( myCol.ContainsKey( "green" ) )
         myCol.Remove( "green" );
      Console.WriteLine( "The collection contains the following elements after removing \"green\":" );
      PrintKeysAndValues1( myCol );

      // Clears the entire collection.
      myCol.Clear();
      Console.WriteLine( "The collection contains the following elements after it is cleared:" );
      PrintKeysAndValues1( 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

Displays the elements in the array:
   KEY        VALUE
   red        rojo
   blue       azul
   green      verde

The collection does not contain the value "amarillo".

The collection contains the following elements after removing "green":
   KEY                       VALUE
   red                       rojo
   blue                      azul

The collection contains the following elements after it is cleared:
   KEY                       VALUE

*/

import System.*;
import System.Collections.*; 
import System.Collections.Specialized.*;

public class SamplesStringDictionary
{
    public static void main(String[] args) 
    {
        // 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 for loop.
        // This is the preferred method.
        Console.WriteLine("Displays the elements using for loop:");
        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);
          
        // Copies the StringDictionary to an array with DictionaryEntry 
        // elements.
        DictionaryEntry myArr[] = new DictionaryEntry[myCol.get_Count()];
        myCol.CopyTo(myArr, 0);
             
        // Displays the values in the array.
        Console.WriteLine("Displays the elements in the array:");
        Console.WriteLine("   KEY        VALUE");
        for(int i = 0; i < myArr.length; i++) {
            Console.WriteLine("   {0,-10} {1}", myArr[i].get_Key(), 
                myArr[i].get_Value());
        } 
        Console.WriteLine();
          
        // Searches for a value.
        if (myCol.ContainsValue("amarillo")) {
            Console.WriteLine("The collection contains the value \"amarillo\".");
        }
        else {
            Console.WriteLine("The collection does not contain the value "
                + "\"amarillo\".");
        }
        Console.WriteLine();
          
        // Searches for a key and deletes it.
        if (myCol.ContainsKey("green")) {
            myCol.Remove("green");
        }
        Console.WriteLine("The collection contains the following elements after"
            + " removing \"green\":");
        PrintKeysAndValues1(myCol);
          
        // Clears the entire collection.
        myCol.Clear();
        Console.WriteLine("The collection contains the following elements"  
            + " after it is cleared:");
        PrintKeysAndValues1(myCol);
    } //main

    // Uses the for statement which hides the complexity of the enumerator.
    // NOTE: The for statement is the preferred way of enumerating the contents 
    // of a collection.
    public static void PrintKeysAndValues1(StringDictionary myCol)
    {
        String strValue;
        String strKeys[] = new String[myCol.get_Count()];
        myCol.get_Keys().CopyTo(strKeys, 0);

        Console.WriteLine("   KEY                       VALUE");
        for (int iCtr = 0; iCtr < myCol.get_Count(); iCtr++) {
            strValue = myCol.get_Item(strKeys[iCtr]);
            Console.WriteLine("   {0,-25} {1}", strKeys[iCtr], strValue);
        }
        Console.WriteLine();
    } //PrintKeysAndValues1
   
    // Uses the enumerator. 
    // NOTE: The for 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.get_Current()));
            Console.WriteLine("   {0,-25} {1}", de.get_Key(), de.get_Value());
        }
        Console.WriteLine();
    } //PrintKeysAndValues2
      
    // Uses the Keys, Values, Count, and Item properties.
    public static void PrintKeysAndValues3(StringDictionary myCol) 
    {
        String myKeys[] = new String[myCol.get_Count()];
        myCol.get_Keys().CopyTo(myKeys, 0);
      
        Console.WriteLine("   INDEX KEY                       VALUE");
        for(int i = 0; i < myCol.get_Count(); i++) {
            Console.WriteLine("   {0,-5} {1,-25} {2}", (Int32)i, myKeys[i], 
                myCol.get_Item(myKeys[i]));
        } 
        Console.WriteLine();
    } //PrintKeysAndValues3
} //SamplesStringDictionary
 
/*
This code produces the following output.

Displays the elements using for loop:
   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

Displays the elements in the array:
   KEY        VALUE
   red        rojo
   blue       azul
   green      verde

The collection does not contain the value "amarillo".

The collection contains the following elements after removing "green":
   KEY                       VALUE
   red                       rojo
   blue                      azul

The collection contains the following elements after it is cleared:
   KEY                       VALUE

*/

System.Object
  System.Collections.Specialized.StringDictionary

Public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

This implementation does not provide a synchronized (thread safe) wrapper for a StringDictionary, but derived classes can create their own synchronized versions of the StringDictionary using the SyncRoot property.

Enumerating through a collection is intrinsically not a thread-safe procedure. Even when a collection is synchronized, other threads can still modify the collection, which causes the enumerator to throw an exception. To guarantee thread safety during enumeration, you can either lock the collection during the entire enumeration or catch the exceptions resulting from changes made by other threads.

Windows 98, Windows Server 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.

.NET Framework

Supported in: 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 2.0

XNA Framework

Supported in: 1.0
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