CollectionBase.System.Collections.IList.Item Property
Note: This namespace, class, or member is supported only in version 1.1 of the .NET Framework.
Gets or sets the element at the specified index.
[C#] In C#, this property is the indexer for the CollectionBase class.
Private Default Property Item( _
ByVal index As Integer _) As Object Implements IList.Item
[C#]
object IList.this[
intindex] {get; set;}
[C++]
private: __property Object* System::Collections::IList::get_Item(intindex);private: __property void System::Collections::IList::set_Item(intindex, Object*);
[JScript]
private function get IList.get_Item(index : int) : Object;private function set IList.set_Item(index : int, value : Object);-or-private function get IList.get_Item(index : int) : Object;private function set IList.set_Item(index : int, value : Object);
[JScript] In JScript, you can use the default indexed properties defined by a type, but you cannot explicitly define your own. However, specifying the expando attribute on a class automatically provides a default indexed property whose type is Object and whose index type is String.
Arguments [JScript]
- index
The zero-based index of the element to get or set.
Parameters [Visual Basic, C#, C++]
- index
The zero-based index of the element to get or set.
Property Value
The element at the specified index.
Implements
Exceptions
| Exception Type | Condition |
|---|---|
| ArgumentOutOfRangeException | index is less than zero.
-or- index is equal to or greater than Count. |
Remarks
This property provides the ability to access a specific element in the collection by using the following syntax: myCollection[index].
Example
[Visual Basic, C#, C++] The following code example implements the CollectionBase class and uses that implementation to create a collection of Int16 objects.
Imports System
Imports System.Collections
Public Class Int16Collection
Inherits CollectionBase
Default Public Property Item(index As Integer) As Int16
Get
Return CType(List(index), Int16)
End Get
Set
List(index) = value
End Set
End Property
Public Function Add(value As Int16) As Integer
Return List.Add(value)
End Function 'Add
Public Function IndexOf(value As Int16) As Integer
Return List.IndexOf(value)
End Function 'IndexOf
Public Sub Insert(index As Integer, value As Int16)
List.Insert(index, value)
End Sub 'Insert
Public Sub Remove(value As Int16)
List.Remove(value)
End Sub 'Remove
Public Function Contains(value As Int16) As Boolean
' If value is not of type Int16, this will return false.
Return List.Contains(value)
End Function 'Contains
Protected Overrides Sub OnInsert(index As Integer, value As [Object])
' Insert additional code to be run only when inserting values.
End Sub 'OnInsert
Protected Overrides Sub OnRemove(index As Integer, value As [Object])
' Insert additional code to be run only when removing values.
End Sub 'OnRemove
Protected Overrides Sub OnSet(index As Integer, oldValue As [Object], newValue As [Object])
' Insert additional code to be run only when setting values.
End Sub 'OnSet
Protected Overrides Sub OnValidate(value As [Object])
If Not value.GetType() Is Type.GetType("System.Int16") Then
Throw New ArgumentException("value must be of type Int16.", "value")
End If
End Sub 'OnValidate
End Class 'Int16Collection
Public Class SamplesCollectionBase
Public Shared Sub Main()
' Creates and initializes a new CollectionBase.
Dim myI16 As New Int16Collection()
' Adds elements to the collection.
myI16.Add( 1 )
myI16.Add( 2 )
myI16.Add( 3 )
myI16.Add( 5 )
myI16.Add( 7 )
' Displays the contents of the collection using the enumerator.
Console.WriteLine("Initial contents of the collection:")
PrintIndexAndValues(myI16)
' Searches the collection with Contains and IndexOf.
Console.WriteLine("Contains 3: {0}", myI16.Contains(3))
Console.WriteLine("2 is at index {0}.", myI16.IndexOf(2))
Console.WriteLine()
' Inserts an element into the collection at index 3.
myI16.Insert(3, 13)
Console.WriteLine("Contents of the collection after inserting at index 3:")
PrintIndexAndValues(myI16)
' Gets and sets an element using the index.
myI16(4) = 123
Console.WriteLine("Contents of the collection after setting the element at index 4 to 123:")
PrintIndexAndValues(myI16)
' Removes an element from the collection.
myI16.Remove(2)
' Displays the contents of the collection using the index.
Console.WriteLine("Contents of the collection after removing the element 2:")
Dim i As Integer
For i = 0 To myI16.Count - 1
Console.WriteLine(" [{0}]: {1}", i, myI16(i))
Next i
End Sub 'Main
Public Shared Sub PrintIndexAndValues(myCol As Int16Collection)
Dim i As Integer = 0
Dim myEnumerator As System.Collections.IEnumerator = myCol.GetEnumerator()
While myEnumerator.MoveNext()
Console.WriteLine(" [{0}]: {1}", i, myEnumerator.Current)
i += 1
End While
Console.WriteLine()
End Sub 'PrintIndexAndValues
End Class 'SamplesCollectionBase
'This code produces the following output.
'
'Initial contents of the collection:
' [0]: 1
' [1]: 2
' [2]: 3
' [3]: 5
' [4]: 7
'
'Contains 3: True
'2 is at index 1.
'
'Contents of the collection after inserting at index 3:
' [0]: 1
' [1]: 2
' [2]: 3
' [3]: 13
' [4]: 5
' [5]: 7
'
'Contents of the collection after setting the element at index 4 to 123:
' [0]: 1
' [1]: 2
' [2]: 3
' [3]: 13
' [4]: 123
' [5]: 7
'
'Contents of the collection after removing the element 2:
' [0]: 1
' [1]: 3
' [2]: 13
' [3]: 123
' [4]: 7
[C#]
using System;
using System.Collections;
public class Int16Collection : CollectionBase {
public Int16 this[ int index ] {
get {
return( (Int16) List[index] );
}
set {
List[index] = value;
}
}
public int Add( Int16 value ) {
return( List.Add( value ) );
}
public int IndexOf( Int16 value ) {
return( List.IndexOf( value ) );
}
public void Insert( int index, Int16 value ) {
List.Insert( index, value );
}
public void Remove( Int16 value ) {
List.Remove( value );
}
public bool Contains( Int16 value ) {
// If value is not of type Int16, this will return false.
return( List.Contains( value ) );
}
protected override void OnInsert( int index, Object value ) {
// Insert additional code to be run only when inserting values.
}
protected override void OnRemove( int index, Object value ) {
// Insert additional code to be run only when removing values.
}
protected override void OnSet( int index, Object oldValue, Object newValue ) {
// Insert additional code to be run only when setting values.
}
protected override void OnValidate( Object value ) {
if ( value.GetType() != Type.GetType("System.Int16") )
throw new ArgumentException( "value must be of type Int16.", "value" );
}
}
public class SamplesCollectionBase {
public static void Main() {
// Creates and initializes a new CollectionBase.
Int16Collection myI16 = new Int16Collection();
// Adds elements to the collection.
myI16.Add( (Int16) 1 );
myI16.Add( (Int16) 2 );
myI16.Add( (Int16) 3 );
myI16.Add( (Int16) 5 );
myI16.Add( (Int16) 7 );
// Displays the contents of the collection using the enumerator.
Console.WriteLine( "Initial contents of the collection:" );
PrintIndexAndValues( myI16 );
// Searches the collection with Contains and IndexOf.
Console.WriteLine( "Contains 3: {0}", myI16.Contains( 3 ) );
Console.WriteLine( "2 is at index {0}.", myI16.IndexOf( 2 ) );
Console.WriteLine();
// Inserts an element into the collection at index 3.
myI16.Insert( 3, (Int16) 13 );
Console.WriteLine( "Contents of the collection after inserting at index 3:" );
PrintIndexAndValues( myI16 );
// Gets and sets an element using the index.
myI16[4] = 123;
Console.WriteLine( "Contents of the collection after setting the element at index 4 to 123:" );
PrintIndexAndValues( myI16 );
// Removes an element from the collection.
myI16.Remove( (Int16) 2 );
// Displays the contents of the collection using the index.
Console.WriteLine( "Contents of the collection after removing the element 2:" );
for ( int i = 0; i < myI16.Count; i++ ) {
Console.WriteLine( " [{0}]: {1}", i, myI16[i] );
}
}
public static void PrintIndexAndValues( Int16Collection myCol ) {
int i = 0;
System.Collections.IEnumerator myEnumerator = myCol.GetEnumerator();
while ( myEnumerator.MoveNext() )
Console.WriteLine( " [{0}]: {1}", i++, myEnumerator.Current );
Console.WriteLine();
}
}
/*
This code produces the following output.
Initial contents of the collection:
[0]: 1
[1]: 2
[2]: 3
[3]: 5
[4]: 7
Contains 3: True
2 is at index 1.
Contents of the collection after inserting at index 3:
[0]: 1
[1]: 2
[2]: 3
[3]: 13
[4]: 5
[5]: 7
Contents of the collection after setting the element at index 4 to 123:
[0]: 1
[1]: 2
[2]: 3
[3]: 13
[4]: 123
[5]: 7
Contents of the collection after removing the element 2:
[0]: 1
[1]: 3
[2]: 13
[3]: 123
[4]: 7
*/
[C++]
#using <mscorlib.dll>
using namespace System;
using namespace System::Collections;
public __gc class Int16Collection : public CollectionBase
{
public:
__property Int16 get_Item( int index )
{
return *__try_cast<__box Int16*>(List->Item[index]);
}
__property void set_Item( int index, Int16 value )
{
List->Item[index] = __box(value);
}
int Add(Int16 value)
{
return(List->Add(__box(value)));
}
int IndexOf(Int16 value)
{
return(List->IndexOf(__box(value)));
}
void Insert(int index, Int16 value)
{
List->Insert(index, __box(value));
}
void Remove(Int16 value)
{
List->Remove(__box(value));
}
bool Contains(Int16 value)
{
// If value is not of type Int16, this will return false.
return(List->Contains(__box(value)));
}
protected:
void OnInsert(int index, Object* value)
{
// Insert additional code to be run only when inserting values.
}
void OnRemove(int index, Object* value)
{
// Insert additional code to be run only when removing values.
}
void OnSet(int index, Object* oldValue, Object* newValue)
{
// Insert additional code to be run only when setting values.
}
void OnValidate(Object* value)
{
if (value->GetType() != Type::GetType(S"System.Int16"))
throw new ArgumentException(S"value must be of type Int16.", S"value");
}
};
void PrintIndexAndValues(Int16Collection* myCol)
{
int i = 0;
System::Collections::IEnumerator* myEnumerator = myCol->GetEnumerator();
while (myEnumerator->MoveNext())
Console::WriteLine(S" [ {0}]: {1}", __box(i++), myEnumerator->Current);
Console::WriteLine();
}
int main()
{
// Creates and initializes a new CollectionBase.
Int16Collection* myI16 = new Int16Collection();
// Adds elements to the collection.
myI16->Add((Int16) 1);
myI16->Add((Int16) 2);
myI16->Add((Int16) 3);
myI16->Add((Int16) 5);
myI16->Add((Int16) 7);
// Displays the contents of the collection using the enumerator.
Console::WriteLine(S"Initial contents of the collection:");
PrintIndexAndValues(myI16);
// Searches the collection with Contains and IndexOf.
Console::WriteLine(S"Contains 3: {0}", __box(myI16->Contains(3)));
Console::WriteLine(S"2 is at index {0}.", __box(myI16->IndexOf(2)));
Console::WriteLine();
// Inserts an element into the collection at index 3.
myI16->Insert(3, (Int16) 13);
Console::WriteLine(S"Contents of the collection after inserting at index 3:");
PrintIndexAndValues(myI16);
// Gets and sets an element using the index.
myI16->Item[4] = 123;
Console::WriteLine(S"Contents of the collection after setting the element at index 4 to 123:");
PrintIndexAndValues(myI16);
// Removes an element from the collection.
myI16->Remove((Int16) 2);
// Displays the contents of the collection using the index.
Console::WriteLine(S"Contents of the collection after removing the element 2:");
for (int i = 0; i < myI16->Count; i++)
{
Console::WriteLine(S" [ {0}]: {1}", __box(i), __box(myI16->Item[i]));
}
}
/*
This code produces the following output.
Initial contents of the collection:
[0]: 1
[1]: 2
[2]: 3
[3]: 5
[4]: 7
Contains 3: True
2 is at index 1.
Contents of the collection after inserting at index 3:
[0]: 1
[1]: 2
[2]: 3
[3]: 13
[4]: 5
[5]: 7
Contents of the collection after setting the element at index 4 to 123:
[0]: 1
[1]: 2
[2]: 3
[3]: 13
[4]: 123
[5]: 7
Contents of the collection after removing the element 2:
[0]: 1
[1]: 3
[2]: 13
[3]: 123
[4]: 7
*/
[JScript] No example is available for JScript. To view a Visual Basic, C#, or C++ example, click the Language Filter button .gif)
in the upper-left corner of the page.
Requirements
Platforms: Windows 98, Windows NT 4.0, Windows Millennium Edition, Windows 2000, Windows XP Home Edition, Windows XP Professional, Windows Server 2003 family
See Also
CollectionBase Class | CollectionBase Members | System.Collections Namespace | Count