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.NET Framework Class Library
IListItem Property

Gets or sets the element at the specified index.

Namespace:   System.Collections
Assembly:  mscorlib (in mscorlib.dll)
Syntax
Property Item ( _
	index As [%$TOPIC/fda941x1_en-us_VS_110_1_0_0_0_0%] _
) As [%$TOPIC/fda941x1_en-us_VS_110_1_0_0_0_1%]
[%$TOPIC/fda941x1_en-us_VS_110_1_0_1_0_0%] this[
	[%$TOPIC/fda941x1_en-us_VS_110_1_0_1_0_1%] index
] { get; set; }
property [%$TOPIC/fda941x1_en-us_VS_110_1_0_2_0_0%]^ Item[[%$TOPIC/fda941x1_en-us_VS_110_1_0_2_0_1%] index] {
	[%$TOPIC/fda941x1_en-us_VS_110_1_0_2_0_2%]^ get ([%$TOPIC/fda941x1_en-us_VS_110_1_0_2_0_3%] index);
	void set ([%$TOPIC/fda941x1_en-us_VS_110_1_0_2_0_4%] index, [%$TOPIC/fda941x1_en-us_VS_110_1_0_2_0_5%]^ value);
}
abstract Item : 
        index:[%$TOPIC/fda941x1_en-us_VS_110_1_0_3_0_0%] -> [%$TOPIC/fda941x1_en-us_VS_110_1_0_3_0_1%] with get, set

Parameters

index
Type: SystemInt32

The zero-based index of the element to get or set.

Property Value

Type: SystemObject
The element at the specified index.
Exceptions
ExceptionCondition
ArgumentOutOfRangeException

index is not a valid index in the IList.

NotSupportedException

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

Remarks

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.

Examples

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()

        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
class SimpleList : IList
{
    private object[] _contents = new object[8];
    private int _count;

    public SimpleList()
    {
        _count = 0;
    }

    // IList Members 
    public int Add(object value)
    {
        if (_count < _contents.Length)
        {
            _contents[_count] = value;
            _count++;

            return (_count - 1);
        }
        else
        {
            return -1;
        }
    }

    public void Clear()
    {
        _count = 0;
    }

    public bool Contains(object value)
    {
        bool inList = false;
        for (int i = 0; i < Count; i++)
        {
            if (_contents[i] == value)
            {
                inList = true;
                break;
            }
        }
        return inList;
    }

    public int IndexOf(object value)
    {
        int itemIndex = -1;
        for (int i = 0; i < Count; i++)
        {
            if (_contents[i] == value)
            {
                itemIndex = i;
                break;
            }
        }
        return itemIndex;
    }

    public void Insert(int index, object value)
    {
        if ((_count + 1 <= _contents.Length) && (index < Count) && (index >= 0))
        {
            _count++;

            for (int i = Count - 1; i > index; i--)
            {
                _contents[i] = _contents[i - 1];
            }
            _contents[index] = value;
        }
    }

    public bool IsFixedSize
    {
        get
        {
            return true;
        }
    }

    public bool IsReadOnly
    {
        get
        {
            return false;
        }
    }

    public void Remove(object value)
    {
        RemoveAt(IndexOf(value));
    }

    public void RemoveAt(int index)
    {
        if ((index >= 0) && (index < Count))
        {
            for (int i = index; i < Count - 1; i++)
            {
                _contents[i] = _contents[i + 1];
            }
            _count--;
        }
    }

    public object this[int index]
    {
        get
        {
            return _contents[index];
        }
        set
        {
            _contents[index] = value;
        }
    }

    // ICollection Members 

    public void CopyTo(Array array, int index)
    {
        int j = index;
        for (int i = 0; i < Count; i++)
        {
            array.SetValue(_contents[i], j);
            j++;
        }
    }

    public int Count
    {
        get
        {
            return _count;
        }
    }

    public bool IsSynchronized
    {
        get
        {
            return false;
        }
    }

    // Return the current instance since the underlying store is not 
    // publicly available. 
    public object SyncRoot
    {
        get
        {
            return this;
        }
    }

    // IEnumerable Members 

    public IEnumerator GetEnumerator()
    {
        // Refer to the IEnumerator documentation for an example of 
        // implementing an enumerator. 
        throw new Exception("The method or operation is not implemented.");
    }

    public void PrintContents()
    {
        Console.WriteLine("List has a capacity of {0} and currently has {1} elements.", _contents.Length, _count);
        Console.Write("List contents:");
        for (int i = 0; i < Count; i++)
        {
            Console.Write(" {0}", _contents[i]);
        }
        Console.WriteLine();
    }
}
Version Information

.NET Framework

Supported in: 4.6, 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

Supported in: Windows Phone 8.1

Supported in: Windows Phone Silverlight 8.1

Supported in: Windows Phone Silverlight 8
Platforms

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.