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HybridDictionary Class

Implements IDictionary by using a ListDictionary while the collection is small, and then switching to a Hashtable when the collection gets large.

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

'Declaration
<SerializableAttribute> _
Public Class HybridDictionary _
	Implements IDictionary, ICollection, IEnumerable
'Usage
Dim instance As HybridDictionary

This class is recommended for cases where the number of elements in a dictionary is unknown. It takes advantage of the improved performance of a ListDictionary with small collections, and offers the flexibility of switching to a Hashtable which handles larger collections better than ListDictionary.

If the initial size of the collection is greater than the optimal size for a ListDictionary, the collection is stored in a Hashtable to avoid the overhead of copying elements from the ListDictionary to a Hashtable.

The constructor accepts a Boolean parameter that allows the user to specify whether the collection ignores the case when comparing strings. If the collection is case-sensitive, it uses the key's implementations of Object.GetHashCode and Object.Equals. If the collection is case-insensitive, it performs a simple ordinal case-insensitive comparison, which obeys the casing rules of the invariant culture only. By default, the collection is case-sensitive. For more information on the invariant culture, see System.Globalization.CultureInfo.

A key cannot be Nothing, but a value can.

[Visual Basic, C#]

The foreach statement of the C# language (for each in Visual Basic) requires the type of each element in the collection. Since each element of the HybridDictionary is a key/value pair, the element type is not the type of the key or the type of the value. Instead, the element type is DictionaryEntry. For example:

For Each de As DictionaryEntry In myHybridDictionary
  ...
Next de

[Visual Basic, C#]

The foreach statement is a wrapper around the enumerator, which only allows reading from, not writing to, the collection.

Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows CE Platform Note: All keys added to a case-insensitive HybridDictionary must have string values.

The following code example demonstrates several of the properties and methods of HybridDictionary.

Imports System
Imports System.Collections
Imports System.Collections.Specialized

Public Class SamplesHybridDictionary   

   Public Shared Sub Main()

      ' Creates and initializes a new HybridDictionary. 
      Dim myCol As New HybridDictionary()
      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")
      myCol.Add("Plantain Bananas", "1.49")
      myCol.Add("Yellow Bananas", "0.79")
      myCol.Add("Strawberries", "3.33")
      myCol.Add("Cranberries", "5.98")
      myCol.Add("Navel Oranges", "1.29")
      myCol.Add("Grapes", "1.99")
      myCol.Add("Honeydew Melon", "0.59")
      myCol.Add("Seedless Watermelon", "0.49")
      myCol.Add("Pineapple", "1.49")
      myCol.Add("Nectarine", "1.99")
      myCol.Add("Plums", "1.69")
      myCol.Add("Peaches", "1.99")

      ' Display the contents of the collection using For Each. This is the preferred method.
      Console.WriteLine("Displays the elements using For Each:")
      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)

      ' Copies the HybridDictionary to an array with DictionaryEntry elements. 
      Dim myArr(myCol.Count) As DictionaryEntry
      myCol.CopyTo(myArr, 0)

      ' Displays the values in the array.
      Console.WriteLine("Displays the elements in the array:")
      Console.WriteLine("   KEY                       VALUE")
      Dim i As Integer 
      For i = 0 To myArr.Length - 1
         Console.WriteLine("   {0,-25} {1}", myArr(i).Key, myArr(i).Value)
      Next i
      Console.WriteLine()

      ' Searches for a key. 
      If myCol.Contains("Kiwis") Then
         Console.WriteLine("The collection contains the key ""Kiwis"".")
      Else
         Console.WriteLine("The collection does not contain the key ""Kiwis"".")
      End If
      Console.WriteLine()

      ' Deletes a key.
      myCol.Remove("Plums")
      Console.WriteLine("The collection contains the following elements after removing ""Plums"":")
      PrintKeysAndValues1(myCol)

      ' Clears the entire collection.
      myCol.Clear()
      Console.WriteLine("The collection contains the following elements after it is cleared:")
      PrintKeysAndValues1(myCol)

   End Sub 'Main

   ' Uses the For Each statement which hides the complexity of the enumerator. 
   ' NOTE: The For Each statement is the preferred way of enumerating the contents of a collection. 
   Public Shared Sub PrintKeysAndValues1(myCol As IDictionary)

      Console.WriteLine("   KEY                       VALUE")
      Dim de As DictionaryEntry
      For Each de In  myCol
         Console.WriteLine("   {0,-25} {1}", de.Key, de.Value)
      Next de
      Console.WriteLine()

   End Sub 'PrintKeysAndValues


   ' Uses the enumerator.  
   ' NOTE: The For Each statement is the preferred way of enumerating the contents of a collection. 
   Public Shared Sub PrintKeysAndValues2(myCol As IDictionary)
      Dim myEnumerator As IDictionaryEnumerator = myCol.GetEnumerator()

      Console.WriteLine("   KEY                       VALUE")
      While myEnumerator.MoveNext()
         Console.WriteLine("   {0,-25} {1}", myEnumerator.Key, myEnumerator.Value)
      End While
      Console.WriteLine()

   End Sub 'PrintKeysAndValues2


   ' Uses the Keys, Values, Count, and Item properties. 
   Public Shared Sub PrintKeysAndValues3(myCol As HybridDictionary)
      Dim myKeys(myCol.Count) As [String]
      myCol.Keys.CopyTo(myKeys, 0)

      Console.WriteLine("   INDEX KEY                       VALUE")
      Dim i As Integer 
      For i = 0 To myCol.Count - 1
         Console.WriteLine("   {0,-5} {1,-25} {2}", i, myKeys(i), myCol(myKeys(i)))
      Next i
      Console.WriteLine()

   End Sub 'PrintKeysAndValues3

End Class 'SamplesHybridDictionary 


'This code produces the following output. 

'Displays the elements using For Each: 
'   KEY                       VALUE 
'   Strawberries              3.33 
'   Yellow Bananas            0.79 
'   Cranberries               5.98 
'   Grapes                    1.99 
'   Granny Smith Apples       0.89 
'   Seedless Watermelon       0.49 
'   Honeydew Melon            0.59 
'   Red Delicious Apples      0.99 
'   Navel Oranges             1.29 
'   Fuji Apples               1.29 
'   Plantain Bananas          1.49 
'   Gala Apples               1.49 
'   Pineapple                 1.49 
'   Plums                     1.69 
'   Braeburn Apples           1.49 
'   Peaches                   1.99 
'   Golden Delicious Apples   1.29 
'   Nectarine                 1.99 

'Displays the elements using the IDictionaryEnumerator: 
'   KEY                       VALUE 
'   Strawberries              3.33 
'   Yellow Bananas            0.79 
'   Cranberries               5.98 
'   Grapes                    1.99 
'   Granny Smith Apples       0.89 
'   Seedless Watermelon       0.49 
'   Honeydew Melon            0.59 
'   Red Delicious Apples      0.99 
'   Navel Oranges             1.29 
'   Fuji Apples               1.29 
'   Plantain Bananas          1.49 
'   Gala Apples               1.49 
'   Pineapple                 1.49 
'   Plums                     1.69 
'   Braeburn Apples           1.49 
'   Peaches                   1.99 
'   Golden Delicious Apples   1.29 
'   Nectarine                 1.99 

'Displays the elements using the Keys, Values, Count, and Item properties: 
'   INDEX KEY                       VALUE 
'   0     Strawberries              3.33 
'   1     Yellow Bananas            0.79 
'   2     Cranberries               5.98 
'   3     Grapes                    1.99 
'   4     Granny Smith Apples       0.89 
'   5     Seedless Watermelon       0.49 
'   6     Honeydew Melon            0.59 
'   7     Red Delicious Apples      0.99 
'   8     Navel Oranges             1.29 
'   9     Fuji Apples               1.29 
'   10    Plantain Bananas          1.49 
'   11    Gala Apples               1.49 
'   12    Pineapple                 1.49 
'   13    Plums                     1.69 
'   14    Braeburn Apples           1.49 
'   15    Peaches                   1.99 
'   16    Golden Delicious Apples   1.29 
'   17    Nectarine                 1.99 

'Displays the elements in the array: 
'   KEY                       VALUE 
'   Strawberries              3.33 
'   Yellow Bananas            0.79 
'   Cranberries               5.98 
'   Grapes                    1.99 
'   Granny Smith Apples       0.89 
'   Seedless Watermelon       0.49 
'   Honeydew Melon            0.59 
'   Red Delicious Apples      0.99 
'   Navel Oranges             1.29 
'   Fuji Apples               1.29 
'   Plantain Bananas          1.49 
'   Gala Apples               1.49 
'   Pineapple                 1.49 
'   Plums                     1.69 
'   Braeburn Apples           1.49 
'   Peaches                   1.99 
'   Golden Delicious Apples   1.29 
'   Nectarine                 1.99 

'The collection does not contain the key "Kiwis". 

'The collection contains the following elements after removing "Plums": 
'   KEY                       VALUE 
'   Strawberries              3.33 
'   Yellow Bananas            0.79 
'   Cranberries               5.98 
'   Grapes                    1.99 
'   Granny Smith Apples       0.89 
'   Seedless Watermelon       0.49 
'   Honeydew Melon            0.59 
'   Red Delicious Apples      0.99 
'   Navel Oranges             1.29 
'   Fuji Apples               1.29 
'   Plantain Bananas          1.49 
'   Gala Apples               1.49 
'   Pineapple                 1.49 
'   Braeburn Apples           1.49 
'   Peaches                   1.99 
'   Golden Delicious Apples   1.29 
'   Nectarine                 1.99 

'The collection contains the following elements after it is cleared: 
'   KEY                       VALUE

System.Object
  System.Collections.Specialized.HybridDictionary
    System.Web.Mobile.CookielessData

Public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

This implementation does not provide a synchronized (thread safe) wrapper for a HybridDictionary, but derived classes can create their own synchronized versions of the HybridDictionary using the SyncRoot property.

Enumerating through a collection is intrinsically not a thread-safe procedure. Even when a collection is synchronized, other threads can still modify the collection, which causes the enumerator to throw an exception. To guarantee thread safety during enumeration, you can either lock the collection during the entire enumeration or catch the exceptions resulting from changes made by other threads.

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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