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StringDictionary.ContainsKey Method

Determines if the StringDictionary contains a specific key.

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

public virtual bool ContainsKey (
	string key
)
public boolean ContainsKey (
	String key
)
public function ContainsKey (
	key : String
) : boolean
Not applicable.

Parameters

key

The key to locate in the StringDictionary.

Return Value

true if the StringDictionary contains an entry with the specified key; otherwise, false.

Exception typeCondition

ArgumentNullException

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

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

This method is an O(1) operation.

Starting with the .NET Framework 2.0, this method uses the collection’s objects’ Equals and CompareTo methods on item to determine whether item exists. In the earlier versions of the .NET Framework, this determination was made by using the Equals and CompareTo methods of the item parameter on the objects in the collection.

The following code example searches for an element in a 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" );

      // Displays the values in the StringDictionary.
      Console.WriteLine( "Initial contents of the StringDictionary:" );
      PrintKeysAndValues( myCol );

      // Searches for a key.
      if ( myCol.ContainsKey( "red" ) )
         Console.WriteLine( "The collection contains the key \"red\"." );
      else
         Console.WriteLine( "The collection does not contain the key \"red\"." );
      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();

   }

   public static void PrintKeysAndValues( StringDictionary myCol )  {
      Console.WriteLine( "   KEY        VALUE" );
      foreach ( DictionaryEntry de in myCol )
         Console.WriteLine( "   {0,-10} {1}", de.Key, de.Value );
      Console.WriteLine();
   }

}

/*
This code produces the following output.

Initial contents of the StringDictionary:
   KEY        VALUE
   green      verde
   red        rojo
   blue       azul

The collection contains the key "red".

The collection does not contain the value "amarillo".

*/

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");
          
        // Displays the values in the StringDictionary.
        Console.WriteLine("Initial contents of the StringDictionary:");
        PrintKeysAndValues(myCol);
          
        // Searches for a key.
        if ( myCol.ContainsKey("red")  ) {
            Console.WriteLine("The collection contains the key \"red\".");
        }
        else {
            Console.WriteLine("The collection does not contain the key "
                + "\"red\".");
        }
        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();
    } //main
        
    public static void PrintKeysAndValues(StringDictionary myCol) 
    {
        Console.WriteLine("   KEY        VALUE");
        IEnumerator objEnum = myCol.GetEnumerator();
        while (objEnum.MoveNext()) {
            DictionaryEntry de = (DictionaryEntry)objEnum.get_Current();
            Console.WriteLine("   {0,-10} {1}", de.get_Key(), de.get_Value());
        }
        Console.WriteLine();
    } //PrintKeysAndValues
} //SamplesStringDictionary
 
/*
This code produces the following output.

Initial contents of the StringDictionary:
   KEY        VALUE
   red        rojo
   blue       azul
   green      verde

The collection contains the key "red".

The collection does not contain the value "amarillo".

*/

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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