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ListDictionary.Item Property

Gets or sets the value associated with the specified key.

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

public Object this [
	Object key
] { get; set; }
/** @property */
public final Object get_Item (Object key)

/** @property */
public final void set_Item (Object key, Object value)

Not applicable.

Parameters

key

The key whose value to get or set.

Property Value

The value associated with the specified key. If the specified key is not found, attempting to get it returns a null reference (Nothing in Visual Basic), and attempting to set it creates a new entry using the specified key.

Exception typeCondition

ArgumentNullException

key is a null reference (Nothing in Visual Basic).

This property provides the ability to access a specific element in the collection by using the following syntax: myCollection[key].

You can also use the Item property to add new elements by setting the value of a key that does not exist in the ListDictionary; for example, myCollection["myNonexistentKey"] = myValue. However, if the specified key already exists in the ListDictionary, setting the Item property overwrites the old value. In contrast, the Add method does not modify existing elements.

A key cannot be a null reference (Nothing in Visual Basic), but a value can. To distinguish between a null reference (Nothing in Visual Basic) that is returned because the specified key is not found and a null reference (Nothing in Visual Basic) that is returned because the value of the specified key is a null reference (Nothing in Visual Basic), use the Contains method to determine if the key exists in the list.

The C# language uses the this keyword to define the indexers instead of implementing the Item property. Visual Basic implements Item as a default property, which provides the same indexing functionality.

This method is an O(n) operation, where n is Count.

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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