For the generic version of this collection, see System.Collections.Generic..::.SortedList<(Of <(TKey, TValue>)>).

A SortedList element can be accessed by its key, like an element in any IDictionary implementation, or by its index, like an element in any IList implementation.

A SortedList object internally maintains two arrays to store the elements of the list; that is, one array for the keys and another array for the associated values. Each element is a key/value pair that can be accessed as a DictionaryEntry object. A key cannot be nullNothingnullptra null reference (Nothing in Visual Basic), but a value can be.

The capacity of a SortedList object is the number of elements the SortedList can hold. As elements are added to a SortedList, the capacity is automatically increased as required through reallocation. The capacity can be decreased by calling TrimToSize or by setting the Capacity property explicitly.

The elements of a SortedList object are sorted by the keys either according to a specific IComparer implementation specified when the SortedList is created or according to the IComparable implementation provided by the keys themselves. In either case, a SortedList does not allow duplicate keys.

The index sequence is based on the sort sequence. When an element is added, it is inserted into SortedList in the correct sort order, and the indexing adjusts accordingly. When an element is removed, the indexing also adjusts accordingly. Therefore, the index of a specific key/value pair might change as elements are added or removed from the SortedList object.

Operations on a SortedList object tend to be slower than operations on a Hashtable object because of the sorting. However, the SortedList offers more flexibility by allowing access to the values either through the associated keys or through the indexes.

Elements in this collection can be accessed using an integer index. Indexes in this collection are zero-based.

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 SortedList object is a key/value pair, the element type is not the type of the key or the type of the value. Rather, the element type is DictionaryEntry. For example:

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

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

The following code example shows how to create and initialize a SortedList object and how to print out its keys and values.

Imports System
Imports System.Collections
Imports Microsoft.VisualBasic

Public Class SamplesSortedList    

    Public Shared Sub Main()

        ' Creates and initializes a new SortedList.
        Dim mySL As New SortedList()
        mySL.Add("Third", "!")
        mySL.Add("Second", "World")
        mySL.Add("First", "Hello")

        ' Displays the properties and values of the SortedList.
        Console.WriteLine("mySL")
        Console.WriteLine("  Count:    {0}", mySL.Count)
        Console.WriteLine("  Capacity: {0}", mySL.Capacity)
        Console.WriteLine("  Keys and Values:")
        PrintKeysAndValues(mySL)
    End Sub

    Public Shared Sub PrintKeysAndValues(myList As SortedList)
        Console.WriteLine(ControlChars.Tab & "-KEY-" & ControlChars.Tab & _
           "-VALUE-")
        Dim i As Integer
        For i = 0 To myList.Count - 1
            Console.WriteLine(ControlChars.Tab & "{0}:" & ControlChars.Tab & _
               "{1}", myList.GetKey(i), myList.GetByIndex(i))
        Next i
        Console.WriteLine()
    End Sub
End Class

' This code produces the following output.
' 
' mySL
'   Count:    3
'   Capacity: 16
'   Keys and Values:
'     -KEY-     -VALUE-
'     First:    Hello
'     Second:   World
'     Third:    !

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

A SortedList object can support multiple readers concurrently, as long as the collection is not modified. To guarantee the thread safety of the SortedList, all operations must be done through the wrapper returned by the Synchronized method.

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.

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.NET Framework

.NET Compact Framework

XNA Framework

Reference

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