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Hashtable.ContainsKey Method

Determines whether the Hashtable contains a specific key.

Namespace:  System.Collections
Assembly:  mscorlib (in mscorlib.dll)

public function ContainsKey(
	key : Object
) : boolean

Parameters

key
Type: System.Object

The key to locate in the Hashtable.

Return Value

Type: System.Boolean
true if the Hashtable contains an element with the specified key; otherwise, false.

ExceptionCondition
ArgumentNullException

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

This method behaves exactly as Contains.

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 example shows how to determine whether the Hashtable contains a specific element.

import System
import System.Collections
import Microsoft.VisualBasic

// Creates and initializes a new Hashtable.
var myHT : Hashtable = new Hashtable()
myHT.Add(0, "zero")
myHT.Add(1, "one")
myHT.Add(2, "two")
myHT.Add(3, "three")
myHT.Add(4, "four")

// Displays the values of the Hashtable.
Console.WriteLine("The Hashtable contains the following values:")
PrintIndexAndKeysAndValues(myHT)

// Searches for a specific key.
var msg : String
var myKey : int = 2
if(myHT.ContainsKey(myKey))
    msg = "in the Hashtable"
else
    msg = "NOT in the Hashtable"
Console.WriteLine("The key \"{0}\" is {1}.", myKey, msg)
myKey = 6
if(myHT.ContainsKey(myKey))
    msg = "in the Hashtable"
else
    msg = "NOT in the Hashtable"
Console.WriteLine("The key \"{0}\" is {1}.", myKey, msg)

// Searches for a specific value.
var myValue : String = "three"
if(myHT.ContainsValue(myValue))
    msg = "in the Hashtable"
else
    msg = "NOT in the Hashtable"
Console.WriteLine("The value \"{0}\" is {1}.", myValue, msg)
myValue = "nine"
if(myHT.ContainsValue(myValue))
    msg = "in the Hashtable"
else
    msg = "NOT in the Hashtable"
Console.WriteLine("The value \"{0}\" is {1}.", myValue, msg)

function PrintIndexAndKeysAndValues(myList : Hashtable){
    var myEnumerator : IDictionaryEnumerator = myList.GetEnumerator()
    var i : int = 0
    Console.WriteLine("\t-INDEX-\t-KEY-\t-VALUE-")
    while(myEnumerator.MoveNext()){
        Console.WriteLine("\t[{0}]:\t{1}\t{2}", i++, myEnumerator.Key,
            myEnumerator.Value)
    }
    Console.WriteLine()
}

// This code produces the following output.
// 
// The Hashtable contains the following values:
//     -INDEX-    -KEY-    -VALUE-
//     [0]:       4        four
//     [1]:       3        three
//     [2]:       2        two
//     [3]:       1        one
//     [4]:       0        zero
// 
// The key "2" is in the Hashtable.
// The key "6" is NOT in the Hashtable.
// The value "three" is in the Hashtable.
// The value "nine" is NOT in the Hashtable. 

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 3.5, 2.0, 1.0

XNA Framework

Supported in: 3.0, 2.0, 1.0

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