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IList.Item Property

Gets or sets the element at the specified index.

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

'Declaration
Property Item ( _
	index As Integer _
) As Object

Parameters

index
Type: System.Int32
The zero-based index of the element to get or set.

Property Value

Type: System.Object
The element at the specified index.

ExceptionCondition
ArgumentOutOfRangeException

index is not a valid index in the IList.

NotSupportedException

The property is set and the IList is read-only.

This property provides the ability to access a specific element in the collection by using the following syntax: myCollection[index].

The C# language uses the this keyword to define the indexers instead of implementing the Item property. Visual Basic implements Item as a default property, which provides the same indexing functionality.

The following example demonstrates the implementation of the IList interface to create a simple list, fixed-size list. This code is part of a larger example for the IList interface.


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(ByVal outputBlock As System.Windows.Controls.TextBlock)

      outputBlock.Text += String.Format("List has a capacity of {0} and currently has {1} elements.", _contents.Length - 1, _count) & vbCrLf
      outputBlock.Text &= "List contents:"

      Dim i As Integer
      For i = 0 To Count

         outputBlock.Text += String.Format(" {0}", _contents(i))
      Next i

      outputBlock.Text &= vbCrLf

   End Sub
End Class


Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

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