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StringDictionary.ContainsKey Method

Determines if the StringDictionary contains a specific key.

[Visual Basic]
Public Overridable Function ContainsKey( _
   ByVal key As String _
) As Boolean
[C#]
public virtual bool ContainsKey(
 string key
);
[C++]
public: virtual bool ContainsKey(
 String* key
);
[JScript]
public function ContainsKey(
   key : String
) : Boolean;

Parameters

key
The key to locate in the StringDictionary.

Return Value

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

Exceptions

Exception Type Condition
ArgumentNullException The key is a null reference (Nothing in Visual Basic).

Remarks

This implementation is an O(1) operation.

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

Example

[Visual Basic, C#, C++] The following code example searches for an element in a StringDictionary.

[Visual Basic] 
Imports System
Imports System.Collections
Imports System.Collections.Specialized

Public Class SamplesStringDictionary   

   Public Shared Sub Main()

      ' Creates and initializes a new StringDictionary.
      Dim myCol As 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") Then
         Console.WriteLine("The collection contains the key ""red"".")
      Else
         Console.WriteLine("The collection does not contain the key ""red"".")
      End If
      Console.WriteLine()

      ' Searches for a value.
      If myCol.ContainsValue("amarillo") Then
         Console.WriteLine("The collection contains the value ""amarillo"".")
      Else
         Console.WriteLine("The collection does not contain the value ""amarillo"".")
      End If
      Console.WriteLine()

   End Sub 'Main

   Public Shared Sub PrintKeysAndValues(myCol As StringDictionary)
      Dim de As DictionaryEntry

      Console.WriteLine("   KEY        VALUE")
      For Each de In  myCol
         Console.WriteLine("   {0,-10} {1}", de.Key, de.Value)
      Next de
      Console.WriteLine()

   End Sub 'PrintKeysAndValues

End Class 'SamplesStringDictionary 


'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".


[C#] 
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".

*/

[C++] 
#using <mscorlib.dll>
#using <System.dll>

using namespace System;
using namespace System::Collections;
using namespace System::Collections::Specialized;

void PrintKeysAndValues( StringDictionary* myCol )  {
   Console::WriteLine( S"   KEY        VALUE" );
   IEnumerator* enum0 = myCol->GetEnumerator();
   while (enum0->MoveNext())
   {
      DictionaryEntry* de = __try_cast<DictionaryEntry*>(enum0->Current);
      Console::WriteLine( S"   {0,-10} {1}", de->Key, de->Value );
   }
   Console::WriteLine();
}

int main()  {

   // Creates and initializes a new StringDictionary.
   StringDictionary* myCol = new StringDictionary();
   myCol->Add( S"red", S"rojo" );
   myCol->Add( S"green", S"verde" );
   myCol->Add( S"blue", S"azul" );

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

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

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

*/

[JScript] No example is available for JScript. To view a Visual Basic, C#, or C++ example, click the Language Filter button Language Filter in the upper-left corner of the page.

Requirements

Platforms: Windows 98, Windows NT 4.0, Windows Millennium Edition, Windows 2000, Windows XP Home Edition, Windows XP Professional, Windows Server 2003 family

See Also

StringDictionary Class | StringDictionary Members | System.Collections.Specialized Namespace | Performing Culture-Insensitive String Operations

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