IList.Item Property
Microsoft Silverlight will reach end of support after October 2021. Learn more.
Gets or sets the element at the specified index.
Namespace: System.Collections
Assembly: mscorlib (in mscorlib.dll)
Syntax
'Declaration
Property Item ( _
index As Integer _
) As Object
Object this[
int index
] { get; set; }
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.
Exceptions
| Exception | Condition |
|---|---|
| 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(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
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(System.Windows.Controls.TextBlock outputBlock)
{
outputBlock.Text += String.Format("List has a capacity of {0} and currently has {1} elements.", _contents.Length, _count) + "\n";
outputBlock.Text += "List contents:";
for (int i = 0; i < Count; i++)
{
outputBlock.Text += String.Format(" {0}", _contents[i]);
}
outputBlock.Text += "\n";
}
}
Version Information
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
Platforms
For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.