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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

The IList type exposes the following members.

  NameDescription
Public propertySupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsCountGets the number of elements contained in the ICollection. (Inherited from ICollection.)
Public propertySupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsIsFixedSizeGets a value indicating whether the IList has a fixed size.
Public propertySupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsIsReadOnlyGets a value indicating whether the IList is read-only.
Public propertySupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsIsSynchronizedGets a value indicating whether access to the ICollection is synchronized (thread safe). (Inherited from ICollection.)
Public propertySupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsItemGets or sets the element at the specified index.
Public propertySupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsSyncRootGets an object that can be used to synchronize access to the ICollection. (Inherited from ICollection.)
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  NameDescription
Public methodSupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsAddAdds an item to the IList.
Public methodSupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsClearRemoves all items from the IList.
Public methodSupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsContainsDetermines whether the IList contains a specific value.
Public methodSupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsCopyToCopies the elements of the ICollection to an Array, starting at a particular Array index. (Inherited from ICollection.)
Public methodSupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsGetEnumeratorReturns an enumerator that iterates through a collection. (Inherited from IEnumerable.)
Public methodSupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsIndexOfDetermines the index of a specific item in the IList.
Public methodSupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsInsertInserts an item to the IList at the specified index.
Public methodSupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsRemoveRemoves the first occurrence of a specific object from the IList.
Public methodSupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsRemoveAtRemoves the IList item at the specified index.
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  NameDescription
Public Extension MethodSupported by Portable Class LibrarySupported in .NET for Windows Store appsAsParallelEnables parallelization of a query. (Defined by ParallelEnumerable.)
Public Extension MethodSupported by Portable Class LibrarySupported in .NET for Windows Store appsAsQueryableConverts an IEnumerable to an IQueryable. (Defined by Queryable.)
Public Extension MethodSupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsCast(Of TResult)Casts the elements of an IEnumerable to the specified type. (Defined by Enumerable.)
Public Extension MethodSupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsOfType(Of TResult)Filters the elements of an IEnumerable based on a specified type. (Defined by Enumerable.)
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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 list, 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

.NET Framework

Supported in: 4.5.1, 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

.NET for Windows Store apps

Supported in: Windows 8

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone 8, Silverlight 8.1

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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