ListDictionary Class
Implements IDictionary using a singly linked list. Recommended for collections that typically contain 10 items or less.
For a list of all members of this type, see ListDictionary Members.
System.Object
System.Collections.Specialized.ListDictionary
[Visual Basic] <Serializable> Public Class ListDictionary Implements IDictionary, ICollection, IEnumerable [C#] [Serializable] public class ListDictionary : IDictionary, ICollection, IEnumerable [C++] [Serializable] public __gc class ListDictionary : public IDictionary, ICollection, IEnumerable [JScript] public Serializable class ListDictionary implements IDictionary, ICollection, IEnumerable
Thread Safety
Public static (Shared in Visual Basic) members of this type are safe for multithreaded operations. Instance members are not guaranteed to be thread-safe.
This implementation does not provide a synchronized (thread-safe) wrapper for a ListDictionary, but derived classes can create their own synchronized versions of the ListDictionary using the SyncRoot property.
Enumerating through a collection is intrinsically not a thread-safe procedure. Even when a collection is synchronized, other threads could 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.
Remarks
This is a simple implementation of IDictionary using a singly linked list. It is smaller and faster than a Hashtable if the number of elements is 10 or less. This should not be used if performance is important for large numbers of elements.
Members, such as Item, Add, Remove, and Contains are O(n) operations, where n is Count.
A key cannot be a null reference (Nothing in Visual Basic), 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 ListDictionary is a key-and-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:
[C#] foreach (DictionaryEntry myDE in myListDictionary) {...} [Visual Basic] Dim myDE As DictionaryEntry For Each myDE In myListDictionary ... Next myDE
[Visual Basic, C#] The foreach statement is a wrapper around the enumerator, which only allows reading from, not writing to, the collection.
Example
[Visual Basic, C#, C++] The following code example demonstrates several of the properties and methods of ListDictionary.
[Visual Basic] Imports System Imports System.Collections Imports System.Collections.Specialized Public Class SamplesListDictionary Public Shared Sub Main() ' Creates and initializes a new ListDictionary. Dim myCol As 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") ' Displays the values in the ListDictionary in three different ways. Console.WriteLine("Displays the elements using for each:") PrintKeysAndValues(myCol) Console.WriteLine("Displays the elements using the IDictionaryEnumerator:") PrintKeysAndValues2(myCol) Console.WriteLine("Displays the elements using the Keys, Values, Count, and indexer properties:") PrintKeysAndValues3(myCol) ' Copies the ListDictionary 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"":") PrintKeysAndValues(myCol) ' Clears the entire collection. myCol.Clear() Console.WriteLine("The collection contains the following elements after it is cleared:") PrintKeysAndValues(myCol) End Sub 'Main Public Shared Sub PrintKeysAndValues(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 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 Public Shared Sub PrintKeysAndValues3(myCol As ListDictionary) 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 'SamplesListDictionary 'This code produces the following output. ' 'Displays the elements using for each: ' 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 indexer 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 ' 'Displays the elements in the array: ' 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 ' 'The collection does not contain the key "Kiwis". ' 'The collection contains the following elements after removing "Plums": ' 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 ' 'The collection contains the following elements after it is cleared: ' KEY VALUE ' [C#] 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" ); // Displays the values in the ListDictionary in three different ways. Console.WriteLine( "Displays the elements using foreach:" ); PrintKeysAndValues( myCol ); Console.WriteLine( "Displays the elements using the IDictionaryEnumerator:" ); PrintKeysAndValues2( myCol ); Console.WriteLine( "Displays the elements using the Keys, Values, Count, and indexer properties:" ); PrintKeysAndValues3( myCol ); // Copies the ListDictionary to an array with DictionaryEntry elements. DictionaryEntry[] myArr = new DictionaryEntry[myCol.Count]; myCol.CopyTo( myArr, 0 ); // Displays the values in the array. Console.WriteLine( "Displays the elements in the array:" ); Console.WriteLine( " KEY VALUE" ); for ( int i = 0; i < myArr.Length; i++ ) Console.WriteLine( " {0,-25} {1}", myArr[i].Key, myArr[i].Value ); Console.WriteLine(); // Searches for a key. if ( myCol.Contains( "Kiwis" ) ) Console.WriteLine( "The collection contains the key \"Kiwis\"." ); else Console.WriteLine( "The collection does not contain the key \"Kiwis\"." ); Console.WriteLine(); // Deletes a key. myCol.Remove( "Plums" ); Console.WriteLine( "The collection contains the following elements after removing \"Plums\":" ); PrintKeysAndValues( myCol ); // Clears the entire collection. myCol.Clear(); Console.WriteLine( "The collection contains the following elements after it is cleared:" ); PrintKeysAndValues( myCol ); } public static void PrintKeysAndValues( IDictionary myCol ) { Console.WriteLine( " KEY VALUE" ); foreach ( DictionaryEntry de in myCol ) Console.WriteLine( " {0,-25} {1}", de.Key, de.Value ); Console.WriteLine(); } 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(); } 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 indexer 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 Displays the elements in the array: 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 The collection does not contain the key "Kiwis". The collection contains the following elements after removing "Plums": 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 The collection contains the following elements after it is cleared: KEY VALUE */ [C++] #using <mscorlib.dll> #using <System.dll> using namespace System; using namespace System::Collections; using namespace System::Collections::Specialized; void PrintKeysAndValues( IDictionary* myCol ) { Console::WriteLine( S" KEY VALUE" ); IEnumerator* myEnum = myCol->GetEnumerator(); while (myEnum->MoveNext()) { DictionaryEntry de = *__try_cast<DictionaryEntry*>(myEnum->Current); Console::WriteLine( S" {0,-25} {1}", de.Key, de.Value ); } Console::WriteLine(); } void PrintKeysAndValues2( IDictionary* myCol ) { IDictionaryEnumerator* myEnumerator = myCol->GetEnumerator(); Console::WriteLine( S" KEY VALUE" ); while ( myEnumerator->MoveNext() ) Console::WriteLine( S" {0,-25} {1}", myEnumerator->Key, myEnumerator->Value ); Console::WriteLine(); } void PrintKeysAndValues3( ListDictionary* myCol ) { String* myKeys[] = new String*[myCol->Count]; myCol->Keys->CopyTo( myKeys, 0 ); Console::WriteLine( S" INDEX KEY VALUE" ); for ( int i = 0; i < myCol->Count; i++ ) Console::WriteLine( S" {0,-5} {1,-25} {2}", __box(i), myKeys->Item[i], myCol->Item[myKeys[i]] ); Console::WriteLine(); } int main() { // Creates and initializes a new ListDictionary. ListDictionary* myCol = new ListDictionary(); myCol->Add( S"Braeburn Apples", S"1.49" ); myCol->Add( S"Fuji Apples", S"1.29" ); myCol->Add( S"Gala Apples", S"1.49" ); myCol->Add( S"Golden Delicious Apples", S"1.29" ); myCol->Add( S"Granny Smith Apples", S"0.89" ); myCol->Add( S"Red Delicious Apples", S"0.99" ); // Displays the values in the ListDictionary in three different ways. Console::WriteLine( S"Displays the elements using foreach:" ); PrintKeysAndValues( myCol ); Console::WriteLine( S"Displays the elements using the IDictionaryEnumerator:" ); PrintKeysAndValues2( myCol ); Console::WriteLine( S"Displays the elements using the Keys, Values, Count, and indexer properties:" ); PrintKeysAndValues3( myCol ); // Copies the ListDictionary to an array with DictionaryEntry elements. DictionaryEntry myArr[] = new DictionaryEntry[myCol->Count]; myCol->CopyTo( myArr, 0 ); // Displays the values in the array. Console::WriteLine( S"Displays the elements in the array:" ); Console::WriteLine( S" KEY VALUE" ); for ( int i = 0; i < myArr->Length; i++ ) Console::WriteLine( S" {0,-25} {1}", myArr[i].Key, myArr[i].Value ); Console::WriteLine(); // Searches for a key. if ( myCol->Contains( S"Kiwis" ) ) Console::WriteLine( S"The collection contains the key \"Kiwis\"." ); else Console::WriteLine( S"The collection does not contain the key \"Kiwis\"." ); Console::WriteLine(); // Deletes a key. myCol->Remove( S"Plums" ); Console::WriteLine( S"The collection contains the following elements after removing \"Plums\":" ); PrintKeysAndValues( myCol ); // Clears the entire collection. myCol->Clear(); Console::WriteLine( S"The collection contains the following elements after it is cleared:" ); PrintKeysAndValues( myCol ); } /* 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 indexer 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 Displays the elements in the array: 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 The collection does not contain the key "Kiwis". The collection contains the following elements after removing "Plums": 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 The collection contains the following elements after it is cleared: KEY VALUE */
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Requirements
Namespace: System.Collections.Specialized
Platforms: Windows 98, Windows NT 4.0, Windows Millennium Edition, Windows 2000, Windows XP Home Edition, Windows XP Professional, Windows Server 2003 family, .NET Compact Framework
Assembly: System (in System.dll)
See Also
ListDictionary Members | System.Collections.Specialized Namespace | IDictionary | Hashtable | Performing Culture-Insensitive String Operations