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ListDictionary.GetEnumerator Method

Returns an IDictionaryEnumerator that iterates through the ListDictionary.

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

public IDictionaryEnumerator GetEnumerator ()
public final IDictionaryEnumerator GetEnumerator ()
public final function GetEnumerator () : IDictionaryEnumerator
Not applicable.

Return Value

An IDictionaryEnumerator for the ListDictionary.

The foreach statement of the C# language (for each in Visual Basic) hides the complexity of the enumerators. Therefore, using foreach is recommended, instead of directly manipulating the enumerator.

Enumerators can be used to read the data in the collection, but they cannot be used to modify the underlying collection.

Initially, the enumerator is positioned before the first element in the collection. Reset also brings the enumerator back to this position. At this position, Current is undefined. Therefore, you must call MoveNext to advance the enumerator to the first element of the collection before reading the value of Current.

Current returns the same object until either MoveNext or Reset is called. MoveNext sets Current to the next element.

If MoveNext passes the end of the collection, the enumerator is positioned after the last element in the collection and MoveNext returns false. When the enumerator is at this position, subsequent calls to MoveNext also return false. If the last call to MoveNext returned false, Current is undefined. To set Current to the first element of the collection again, you can call Reset followed by MoveNext.

An enumerator remains valid as long as the collection remains unchanged. If changes are made to the collection, such as adding, modifying, or deleting elements, the enumerator is irrecoverably invalidated and its behavior is undefined.

The enumerator does not have exclusive access to the collection; therefore, enumerating through a collection is intrinsically not a thread-safe procedure. To guarantee thread safety during enumeration, you can lock the collection during the entire enumeration. To allow the collection to be accessed by multiple threads for reading and writing, you must implement your own synchronization.

This method is an O(1) operation.

The following code example enumerates the elements of a ListDictionary.

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

public class SamplesListDictionary  {

   public static void Main()  {

      // Creates and initializes a new ListDictionary.
      ListDictionary myCol = new ListDictionary();
      myCol.Add( "Braeburn Apples", "1.49" );
      myCol.Add( "Fuji Apples", "1.29" );
      myCol.Add( "Gala Apples", "1.49" );
      myCol.Add( "Golden Delicious Apples", "1.29" );
      myCol.Add( "Granny Smith Apples", "0.89" );
      myCol.Add( "Red Delicious Apples", "0.99" );

      // 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 IDictionaryEnumerator:" );
      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( IDictionary 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( IDictionary myCol )  {
      IDictionaryEnumerator myEnumerator = myCol.GetEnumerator();
      Console.WriteLine( "   KEY                       VALUE" );
      while ( myEnumerator.MoveNext() )
         Console.WriteLine( "   {0,-25} {1}", myEnumerator.Key, myEnumerator.Value );
      Console.WriteLine();
   }

   // Uses the Keys, Values, Count, and Item properties.
   public static void PrintKeysAndValues3( ListDictionary 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
   Braeburn Apples           1.49
   Fuji Apples               1.29
   Gala Apples               1.49
   Golden Delicious Apples   1.29
   Granny Smith Apples       0.89
   Red Delicious Apples      0.99

Displays the elements using the IDictionaryEnumerator:
   KEY                       VALUE
   Braeburn Apples           1.49
   Fuji Apples               1.29
   Gala Apples               1.49
   Golden Delicious Apples   1.29
   Granny Smith Apples       0.89
   Red Delicious Apples      0.99

Displays the elements using the Keys, Values, Count, and Item properties:
   INDEX KEY                       VALUE
   0     Braeburn Apples           1.49
   1     Fuji Apples               1.29
   2     Gala Apples               1.49
   3     Golden Delicious Apples   1.29
   4     Granny Smith Apples       0.89
   5     Red Delicious Apples      0.99

*/


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

public class SamplesListDictionary
{
    public static void main(String[] args)
    {
        // Creates and initializes a new ListDictionary.
        ListDictionary myCol = new ListDictionary();

        myCol.Add("Braeburn Apples", "1.49");
        myCol.Add("Fuji Apples", "1.29");
        myCol.Add("Gala Apples", "1.49");
        myCol.Add("Golden Delicious Apples", "1.29");
        myCol.Add("Granny Smith Apples", "0.89");
        myCol.Add("Red Delicious Apples", "0.99");

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

        // Display the contents of the collection using the enumerator.
        Console.WriteLine("Displays the elements using the"
            + " IDictionaryEnumerator:");
        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);
    } //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(IDictionary myCol)
    {
        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++) {
            Console.WriteLine("   {0,-25} {1}", strKeys[iCtr],
                myCol.get_Item(strKeys[iCtr]));
        }
        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(IDictionary myCol)
    {
        IDictionaryEnumerator myEnumerator = myCol.GetEnumerator();

        Console.WriteLine("   KEY                       VALUE");
        while (myEnumerator.MoveNext()) {
            Console.WriteLine("   {0,-25} {1}", myEnumerator.get_Key(),
            myEnumerator.get_Value());
        }

        Console.WriteLine();
    } //PrintKeysAndValues2

    // Uses the Keys, Values, Count, and Item properties.
    public static void PrintKeysAndValues3(ListDictionary 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
}//SamplesListDictionary
 
/*
This code produces the following output.

Displays the elements using for:
   KEY                       VALUE
   Braeburn Apples           1.49
   Fuji Apples               1.29
   Gala Apples               1.49
   Golden Delicious Apples   1.29
   Granny Smith Apples       0.89
   Red Delicious Apples      0.99

Displays the elements using the IDictionaryEnumerator:
   KEY                       VALUE
   Braeburn Apples           1.49
   Fuji Apples               1.29
   Gala Apples               1.49
   Golden Delicious Apples   1.29
   Granny Smith Apples       0.89
   Red Delicious Apples      0.99

Displays the elements using the Keys, Values, Count, and Item properties:
   INDEX KEY                       VALUE
   0     Braeburn Apples           1.49
   1     Fuji Apples               1.29
   2     Gala Apples               1.49
   3     Golden Delicious Apples   1.29
   4     Granny Smith Apples       0.89
   5     Red Delicious Apples      0.99

*/

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, 1.0

XNA Framework

Supported in: 1.0

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