Collection<T>.SetItem(Int32, T) Méthode
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Remplace l'élément à l'index spécifié.
protected:
virtual void SetItem(int index, T item);
protected virtual void SetItem (int index, T item);
abstract member SetItem : int * 'T -> unit
override this.SetItem : int * 'T -> unit
Protected Overridable Sub SetItem (index As Integer, item As T)
- index
- Int32
Index de base zéro de l'élément à remplacer.
- item
- T
Nouvelle valeur de l'élément à l'index spécifié. La valeur peut être null
pour les types référence.
L’exemple de code suivant montre comment dériver une classe de collection à partir d’un type construit de la Collection<T> classe générique, et comment remplacer les méthodes protégées InsertItem, RemoveItem, ClearItemset SetItem pour fournir un comportement personnalisé pour les Addméthodes , Insert, Remove, et Clear pour définir la Item[] propriété.
Le comportement personnalisé fourni par cet exemple est un Changed
événement de notification déclenché à la fin de chacune des méthodes protégées. La Dinosaurs
classe hérite Collection<string>
(Collection(Of String)
en Visual Basic) et définit l’événement Changed
, qui utilise une DinosaursChangedEventArgs
classe pour les informations sur l’événement et une énumération pour identifier le type de modification.
L’exemple de code appelle plusieurs propriétés et méthodes de Collection<T> pour illustrer l’événement personnalisé.
using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
public class Dinosaurs : Collection<string>
{
public event EventHandler<DinosaursChangedEventArgs> Changed;
protected override void InsertItem(int index, string newItem)
{
base.InsertItem(index, newItem);
EventHandler<DinosaursChangedEventArgs> temp = Changed;
if (temp != null)
{
temp(this, new DinosaursChangedEventArgs(
ChangeType.Added, newItem, null));
}
}
protected override void SetItem(int index, string newItem)
{
string replaced = Items[index];
base.SetItem(index, newItem);
EventHandler<DinosaursChangedEventArgs> temp = Changed;
if (temp != null)
{
temp(this, new DinosaursChangedEventArgs(
ChangeType.Replaced, replaced, newItem));
}
}
protected override void RemoveItem(int index)
{
string removedItem = Items[index];
base.RemoveItem(index);
EventHandler<DinosaursChangedEventArgs> temp = Changed;
if (temp != null)
{
temp(this, new DinosaursChangedEventArgs(
ChangeType.Removed, removedItem, null));
}
}
protected override void ClearItems()
{
base.ClearItems();
EventHandler<DinosaursChangedEventArgs> temp = Changed;
if (temp != null)
{
temp(this, new DinosaursChangedEventArgs(
ChangeType.Cleared, null, null));
}
}
}
// Event argument for the Changed event.
//
public class DinosaursChangedEventArgs : EventArgs
{
public readonly string ChangedItem;
public readonly ChangeType ChangeType;
public readonly string ReplacedWith;
public DinosaursChangedEventArgs(ChangeType change, string item,
string replacement)
{
ChangeType = change;
ChangedItem = item;
ReplacedWith = replacement;
}
}
public enum ChangeType
{
Added,
Removed,
Replaced,
Cleared
};
public class Demo
{
public static void Main()
{
Dinosaurs dinosaurs = new Dinosaurs();
dinosaurs.Changed += ChangedHandler;
dinosaurs.Add("Psitticosaurus");
dinosaurs.Add("Caudipteryx");
dinosaurs.Add("Compsognathus");
dinosaurs.Add("Muttaburrasaurus");
Display(dinosaurs);
Console.WriteLine("\nIndexOf(\"Muttaburrasaurus\"): {0}",
dinosaurs.IndexOf("Muttaburrasaurus"));
Console.WriteLine("\nContains(\"Caudipteryx\"): {0}",
dinosaurs.Contains("Caudipteryx"));
Console.WriteLine("\nInsert(2, \"Nanotyrannus\")");
dinosaurs.Insert(2, "Nanotyrannus");
Console.WriteLine("\ndinosaurs[2]: {0}", dinosaurs[2]);
Console.WriteLine("\ndinosaurs[2] = \"Microraptor\"");
dinosaurs[2] = "Microraptor";
Console.WriteLine("\nRemove(\"Microraptor\")");
dinosaurs.Remove("Microraptor");
Console.WriteLine("\nRemoveAt(0)");
dinosaurs.RemoveAt(0);
Display(dinosaurs);
}
private static void Display(Collection<string> cs)
{
Console.WriteLine();
foreach( string item in cs )
{
Console.WriteLine(item);
}
}
private static void ChangedHandler(object source,
DinosaursChangedEventArgs e)
{
if (e.ChangeType==ChangeType.Replaced)
{
Console.WriteLine("{0} was replaced with {1}", e.ChangedItem,
e.ReplacedWith);
}
else if(e.ChangeType==ChangeType.Cleared)
{
Console.WriteLine("The dinosaur list was cleared.");
}
else
{
Console.WriteLine("{0} was {1}.", e.ChangedItem, e.ChangeType);
}
}
}
/* This code example produces the following output:
Psitticosaurus was Added.
Caudipteryx was Added.
Compsognathus was Added.
Muttaburrasaurus was Added.
Psitticosaurus
Caudipteryx
Compsognathus
Muttaburrasaurus
IndexOf("Muttaburrasaurus"): 3
Contains("Caudipteryx"): True
Insert(2, "Nanotyrannus")
Nanotyrannus was Added.
dinosaurs[2]: Nanotyrannus
dinosaurs[2] = "Microraptor"
Nanotyrannus was replaced with Microraptor
Remove("Microraptor")
Microraptor was Removed.
RemoveAt(0)
Psitticosaurus was Removed.
Caudipteryx
Compsognathus
Muttaburrasaurus
*/
Imports System.Collections.Generic
Imports System.Collections.ObjectModel
Public Class Dinosaurs
Inherits Collection(Of String)
Public Event Changed As EventHandler(Of DinosaursChangedEventArgs)
Protected Overrides Sub InsertItem( _
ByVal index As Integer, ByVal newItem As String)
MyBase.InsertItem(index, newItem)
RaiseEvent Changed(Me, New DinosaursChangedEventArgs( _
ChangeType.Added, newItem, Nothing))
End Sub
Protected Overrides Sub SetItem(ByVal index As Integer, _
ByVal newItem As String)
Dim replaced As String = Items(index)
MyBase.SetItem(index, newItem)
RaiseEvent Changed(Me, New DinosaursChangedEventArgs( _
ChangeType.Replaced, replaced, newItem))
End Sub
Protected Overrides Sub RemoveItem(ByVal index As Integer)
Dim removedItem As String = Items(index)
MyBase.RemoveItem(index)
RaiseEvent Changed(Me, New DinosaursChangedEventArgs( _
ChangeType.Removed, removedItem, Nothing))
End Sub
Protected Overrides Sub ClearItems()
MyBase.ClearItems()
RaiseEvent Changed(Me, New DinosaursChangedEventArgs( _
ChangeType.Cleared, Nothing, Nothing))
End Sub
End Class
' Event argument for the Changed event.
'
Public Class DinosaursChangedEventArgs
Inherits EventArgs
Public ReadOnly ChangedItem As String
Public ReadOnly ChangeType As ChangeType
Public ReadOnly ReplacedWith As String
Public Sub New(ByVal change As ChangeType, ByVal item As String, _
ByVal replacement As String)
ChangeType = change
ChangedItem = item
ReplacedWith = replacement
End Sub
End Class
Public Enum ChangeType
Added
Removed
Replaced
Cleared
End Enum
Public Class Demo
Public Shared Sub Main()
Dim dinosaurs As New Dinosaurs
AddHandler dinosaurs.Changed, AddressOf ChangedHandler
dinosaurs.Add("Psitticosaurus")
dinosaurs.Add("Caudipteryx")
dinosaurs.Add("Compsognathus")
dinosaurs.Add("Muttaburrasaurus")
Display(dinosaurs)
Console.WriteLine(vbLf & "IndexOf(""Muttaburrasaurus""): {0}", _
dinosaurs.IndexOf("Muttaburrasaurus"))
Console.WriteLine(vbLf & "Contains(""Caudipteryx""): {0}", _
dinosaurs.Contains("Caudipteryx"))
Console.WriteLine(vbLf & "Insert(2, ""Nanotyrannus"")")
dinosaurs.Insert(2, "Nanotyrannus")
Console.WriteLine(vbLf & "dinosaurs(2): {0}", dinosaurs(2))
Console.WriteLine(vbLf & "dinosaurs(2) = ""Microraptor""")
dinosaurs(2) = "Microraptor"
Console.WriteLine(vbLf & "Remove(""Microraptor"")")
dinosaurs.Remove("Microraptor")
Console.WriteLine(vbLf & "RemoveAt(0)")
dinosaurs.RemoveAt(0)
Display(dinosaurs)
End Sub
Private Shared Sub Display(ByVal cs As Collection(Of String))
Console.WriteLine()
For Each item As String In cs
Console.WriteLine(item)
Next item
End Sub
Private Shared Sub ChangedHandler(ByVal source As Object, _
ByVal e As DinosaursChangedEventArgs)
If e.ChangeType = ChangeType.Replaced Then
Console.WriteLine("{0} was replaced with {1}", _
e.ChangedItem, e.ReplacedWith)
ElseIf e.ChangeType = ChangeType.Cleared Then
Console.WriteLine("The dinosaur list was cleared.")
Else
Console.WriteLine("{0} was {1}.", _
e.ChangedItem, e.ChangeType)
End If
End Sub
End Class
' This code example produces the following output:
'
'Psitticosaurus was Added.
'Caudipteryx was Added.
'Compsognathus was Added.
'Muttaburrasaurus was Added.
'
'Psitticosaurus
'Caudipteryx
'Compsognathus
'Muttaburrasaurus
'
'IndexOf("Muttaburrasaurus"): 3
'
'Contains("Caudipteryx"): True
'
'Insert(2, "Nanotyrannus")
'Nanotyrannus was Added.
'
'dinosaurs(2): Nanotyrannus
'
'dinosaurs(2) = "Microraptor"
'Nanotyrannus was replaced with Microraptor
'
'Remove("Microraptor")
'Microraptor was Removed.
'
'RemoveAt(0)
'Psitticosaurus was Removed.
'
'Caudipteryx
'Compsognathus
'Muttaburrasaurus
Collection<T> accepte null
comme valeur valide pour les types de référence et autorise les éléments en double.
Cette méthode est une opération O(1).
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