Was this page helpful?
Your feedback about this content is important. Let us know what you think.
Additional feedback?
1500 characters remaining
IList Interface

IList Interface

Represents a non-generic collection of objects that can be individually accessed by index.

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

'Declaration
<ComVisibleAttribute(True)> _
Public Interface IList _
	Inherits ICollection, IEnumerable
'Usage
Dim instance As IList

IList is a descendant of the ICollection interface and is the base interface of all non-generic lists. IList implementations fall into three categories: read-only, fixed-size, and variable-size. A read-only IList cannot be modified. A fixed-size IList does not allow the addition or removal of elements, but it allows the modification of existing elements. A variable-size IList allows the addition, removal, and modification of elements.

For the generic version of this interface, see System.Collections.Generic.IList(Of T).

The following example demonstrates the implementation of the IList interface to create a simple, fixed-size list.

Imports System
Imports System.Collections

Public Class Program

    Shared Sub Main()

        Dim myList As New SimpleList()

        ' Populate the List
        Console.WriteLine("Populate the List")
        myList.Add("one")
        myList.Add("two")
        myList.Add("three")
        myList.Add("four")
        myList.Add("five")
        myList.Add("six")
        myList.Add("seven")
        myList.Add("eight")
        myList.PrintContents()
        Console.WriteLine()

        ' Remove elements from the list
        Console.WriteLine("Remove elements from the list")
        myList.Remove("six")
        myList.Remove("eight")
        myList.PrintContents()
        Console.WriteLine()

        ' Add an element to the end of the list
        Console.WriteLine("Add an element to the end of the list")
        myList.Add("nine")
        myList.PrintContents()
        Console.WriteLine()

        ' Insert an element into the middle of the list
        Console.WriteLine("Insert an element into the middle of the list")
        myList.Insert(4, "number")
        myList.PrintContents()
        Console.WriteLine()

        ' Check for specific elements in the list
        Console.WriteLine("Check for specific elements in the list")
        Console.WriteLine("List contains 'three': {0}", myList.Contains("three"))
        Console.WriteLine("List contains 'ten': {0}", myList.Contains("ten"))

    End Sub 
End Class ' class Program

Public Class SimpleList
    Implements IList

    Private _contents(8) As Object
    Private _count As Integer 

    Public Sub New()

        _count = 0
    End Sub 

    ' IList Members 
    Public Function Add(ByVal value As Object) As Integer Implements IList.Add

        If (_count < _contents.Length - 1) Then

            _contents(_count) = value
            _count = _count + 1

            Return (_count - 1)

        Else 

            Return -1
        End If 
    End Function 

    Public Sub Clear() Implements IList.Clear
        _count = 0
    End Sub 

    Public Function Contains(ByVal value As Object) As Boolean Implements IList.Contains

        Dim inList As Boolean = False 

        Dim i As Integer 
        For i = 0 To Count

            If _contents(i) = value Then

                inList = True 
                Exit For 

            End If 

        Next i

        Return inList
    End Function 

    Public Function IndexOf(ByVal value As Object) As Integer Implements IList.IndexOf

        Dim itemIndex As Integer = -1

        Dim i As Integer 
        For i = 0 To Count

            If _contents(i) = value Then

                itemIndex = i
                Exit For 

            End If 

        Next i

        Return itemIndex
    End Function 

    Public Sub Insert(ByVal index As Integer, ByVal value As Object) Implements IList.Insert

        If (_count + 1) <= (_contents.Length - 1) And (index < Count) And (index >= 0) Then

            _count = _count + 1

            Dim i As Integer 
            For i = Count - 1 To index

                _contents(i) = _contents(i - 1)
            Next i

            _contents(index) = value
        End If 
    End Sub 

    Public ReadOnly Property IsFixedSize() As Boolean Implements IList.IsFixedSize
        Get 
            Return True 
        End Get 
    End Property 

    Public ReadOnly Property IsReadOnly() As Boolean Implements IList.IsReadOnly

        Get 
            Return False 
        End Get 
    End Property 

    Public Sub Remove(ByVal value As Object) Implements IList.Remove
        RemoveAt(IndexOf(value))
    End Sub 

    Public Sub RemoveAt(ByVal index As Integer) Implements IList.RemoveAt

        If index >= 0 And index < Count Then 

            Dim i As Integer 
            For i = index To Count - 1

                _contents(i) = _contents(i + 1)
            Next i
            _count = _count - 1

        End If 
    End Sub 

    Public Property Item(ByVal index As Integer) As Object Implements IList.Item

        Get 
            Return _contents(index)
        End Get 

        Set(ByVal value As Object)
            _contents(index) = value
        End Set 
    End Property 

    ' ICollection Members 

    Public Sub CopyTo(ByVal array As Array, ByVal index As Integer) Implements ICollection.CopyTo
        Dim j As Integer = index
        Dim i As Integer 
        For i = 0 To Count
            array.SetValue(_contents(i), j)
            j = j + 1
        Next i
    End Sub 

    Public ReadOnly Property Count() As Integer Implements ICollection.Count
        Get 
            Return _count
        End Get 
    End Property 

    Public ReadOnly Property IsSynchronized() As Boolean Implements ICollection.IsSynchronized
        Get 
            Return False 
        End Get 
    End Property 

    ' Return the current instance since the underlying store is not 
    ' publicly available. 
    Public ReadOnly Property SyncRoot() As Object Implements ICollection.SyncRoot
        Get 
            Return Me 
        End Get 
    End Property 

    ' IEnumerable Members 
    Public Function GetEnumerator() As IEnumerator Implements IEnumerable.GetEnumerator

        ' Refer to the IEnumerator documentation for an example of 
        ' implementing an enumerator. 
        Throw New Exception("The method or operation is not implemented.")
    End Function 

    Public Sub PrintContents()

        Console.WriteLine("List has a capacity of {0} and currently has {1} elements.", _contents.Length - 1, _count)
        Console.Write("List contents:")

        Dim i As Integer 
        For i = 0 To Count

            Console.Write(" {0}", _contents(i))
        Next i

        Console.WriteLine()

    End Sub 
End Class 

' This code produces output similar to the following: 
' Populate the List: 
' List has a capacity of 8 and currently has 8 elements. 
' List contents: one two three four five six seven eight 

' Remove elements from the list: 
' List has a capacity of 8 and currently has 6 elements. 
' List contents: one two three four five seven 

' Add an element to the end of the list: 
' List has a capacity of 8 and currently has 7 elements. 
' List contents: one two three four five seven nine 

' Insert an element into the middle of the list: 
' List has a capacity of 8 and currently has 8 elements. 
' List contents: one two three four number five seven nine 

' Check for specific elements in the list: 
' List contains "three": True 
' List contains "ten": False

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

Community Additions

ADD
Show:
© 2015 Microsoft