ArrayList.Item[Int32] Propriété
Définition
Important
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Obtient ou définit l'élément au niveau de l'index spécifié.
public:
virtual property System::Object ^ default[int] { System::Object ^ get(int index); void set(int index, System::Object ^ value); };public virtual object this[int index] { get; set; }public virtual object? this[int index] { get; set; }member this.Item(int) : obj with get, setDefault Public Overridable Property Item(index As Integer) As ObjectParamètres
- index
- Int32
Index de base zéro de l'élément à obtenir ou à définir.
Valeur de propriété
Élément au niveau de l'index spécifié.
Implémente
Exceptions
Exemples
L’exemple de code suivant crée un ArrayList et ajoute plusieurs éléments. L’exemple illustre l’accès aux éléments avec la Item[] propriété (l’indexeur en C#) et la modification d’un élément en affectant une nouvelle valeur à la Item[] propriété pour un index spécifié. L’exemple montre également que la Item[] propriété ne peut pas être utilisée pour accéder ou ajouter des éléments en dehors de la taille actuelle de la liste.
using namespace System;
using namespace System::Collections;
public ref class Example
{
public:
static void Main()
{
// Create an empty ArrayList, and add some elements.
ArrayList^ stringList = gcnew ArrayList();
stringList->Add("a");
stringList->Add("abc");
stringList->Add("abcdef");
stringList->Add("abcdefg");
// The Item property is an indexer, so the property name is
// not required.
Console::WriteLine("Element {0} is \"{1}\"", 2, stringList[2]);
// Assigning a value to the property changes the value of
// the indexed element.
stringList[2] = "abcd";
Console::WriteLine("Element {0} is \"{1}\"", 2, stringList[2]);
// Accessing an element outside the current element count
// causes an exception.
Console::WriteLine("Number of elements in the list: {0}",
stringList->Count);
try
{
Console::WriteLine("Element {0} is \"{1}\"",
stringList->Count, stringList[stringList->Count]);
}
catch (ArgumentOutOfRangeException^ aoore)
{
Console::WriteLine("stringList({0}) is out of range.",
stringList->Count);
}
// You cannot use the Item property to add new elements.
try
{
stringList[stringList->Count] = "42";
}
catch (ArgumentOutOfRangeException^ aoore)
{
Console::WriteLine("stringList({0}) is out of range.",
stringList->Count);
}
Console::WriteLine();
for (int i = 0; i < stringList->Count; i++)
{
Console::WriteLine("Element {0} is \"{1}\"", i,
stringList[i]);
}
Console::WriteLine();
for each (Object^ o in stringList)
{
Console::WriteLine(o);
}
}
};
int main()
{
Example::Main();
}
/*
This code example produces the following output:
Element 2 is "abcdef"
Element 2 is "abcd"
Number of elements in the list: 4
stringList(4) is out of range.
stringList(4) is out of range.
Element 0 is "a"
Element 1 is "abc"
Element 2 is "abcd"
Element 3 is "abcdefg"
a
abc
abcd
abcdefg
*/
using System;
using System.Collections;
public class Example
{
public static void Main()
{
// Create an empty ArrayList, and add some elements.
ArrayList stringList = new ArrayList();
stringList.Add("a");
stringList.Add("abc");
stringList.Add("abcdef");
stringList.Add("abcdefg");
// The Item property is an indexer, so the property name is
// not required.
Console.WriteLine("Element {0} is \"{1}\"", 2, stringList[2]);
// Assigning a value to the property changes the value of
// the indexed element.
stringList[2] = "abcd";
Console.WriteLine("Element {0} is \"{1}\"", 2, stringList[2]);
// Accessing an element outside the current element count
// causes an exception.
Console.WriteLine("Number of elements in the list: {0}",
stringList.Count);
try
{
Console.WriteLine("Element {0} is \"{1}\"",
stringList.Count, stringList[stringList.Count]);
}
catch(ArgumentOutOfRangeException aoore)
{
Console.WriteLine("stringList({0}) is out of range.",
stringList.Count);
}
// You cannot use the Item property to add new elements.
try
{
stringList[stringList.Count] = "42";
}
catch(ArgumentOutOfRangeException aoore)
{
Console.WriteLine("stringList({0}) is out of range.",
stringList.Count);
}
Console.WriteLine();
for (int i = 0; i < stringList.Count; i++)
{
Console.WriteLine("Element {0} is \"{1}\"", i,
stringList[i]);
}
Console.WriteLine();
foreach (object o in stringList)
{
Console.WriteLine(o);
}
}
}
/*
This code example produces the following output:
Element 2 is "abcdef"
Element 2 is "abcd"
Number of elements in the list: 4
stringList(4) is out of range.
stringList(4) is out of range.
Element 0 is "a"
Element 1 is "abc"
Element 2 is "abcd"
Element 3 is "abcdefg"
a
abc
abcd
abcdefg
*/
Imports System.Collections
Public Class Example
Public Shared Sub Main
' Create an empty ArrayList, and add some elements.
Dim stringList As New ArrayList
stringList.Add("a")
stringList.Add("abc")
stringList.Add("abcdef")
stringList.Add("abcdefg")
' Item is the default property, so the property name is
' not required.
Console.WriteLine("Element {0} is ""{1}""", 2, stringList(2))
' Assigning a value to the property changes the value of
' the indexed element.
stringList(2) = "abcd"
Console.WriteLine("Element {0} is ""{1}""", 2, stringList(2))
' Accessing an element outside the current element count
' causes an exception. The ArrayList index is zero-based,
' so the index of the last element is (Count - 1).
Console.WriteLine("Number of elements in the list: {0}", _
stringList.Count)
Try
Console.WriteLine("Element {0} is ""{1}""", _
stringList.Count, _
stringList(stringList.Count))
Catch aoore As ArgumentOutOfRangeException
Console.WriteLine("stringList({0}) is out of range.", _
stringList.Count)
End Try
' You cannot use the Item property to add new elements.
Try
stringList(stringList.Count) = "42"
Catch aoore As ArgumentOutOfRangeException
Console.WriteLine("stringList({0}) is out of range.", _
stringList.Count)
End Try
Console.WriteLine()
For i As Integer = 0 To stringList.Count - 1
Console.WriteLine("Element {0} is ""{1}""", i, stringList(i))
Next
Console.WriteLine()
For Each o As Object In stringList
Console.WriteLine(o)
Next
End Sub
End Class
'
' This code example produces the following output:
'
'Element 2 is "abcdef"
'Element 2 is "abcd"
'Number of elements in the list: 4
'stringList(4) is out of range.
'stringList(4) is out of range.
'
'Element 0 is "a"
'Element 1 is "abc"
'Element 2 is "abcd"
'Element 3 is "abcdefg"
'
'a
'abc
'abcd
'abcdefg
L’exemple suivant utilise explicitement la Item[] propriété pour affecter des valeurs aux éléments de la liste. L’exemple définit une classe qui hérite d’un ArrayList et ajoute une méthode pour brouiller les éléments de liste.
using namespace System;
using namespace System::Collections;
public ref class ScrambleList : public ArrayList
{
public:
static void Main()
{
// Create an empty ArrayList, and add some elements.
ScrambleList^ integerList = gcnew ScrambleList();
for (int i = 0; i < 10; i++)
{
integerList->Add(i);
}
Console::WriteLine("Ordered:\n");
for each (int value in integerList)
{
Console::Write("{0}, ", value);
}
Console::WriteLine("<end>\n\nScrambled:\n");
// Scramble the order of the items in the list.
integerList->Scramble();
for each (int value in integerList)
{
Console::Write("{0}, ", value);
}
Console::WriteLine("<end>\n");
}
void Scramble()
{
int limit = this->Count;
int temp;
int swapindex;
Random^ rnd = gcnew Random();
for (int i = 0; i < limit; i++)
{
// The Item property of ArrayList is the default indexer. Thus,
// this->default[i] and this[i] are used interchangeably.
temp = (int)this->default[i];
swapindex = rnd->Next(0, limit - 1);
this[i] = this->default[swapindex];
this[swapindex] = temp;
}
}
};
int main()
{
ScrambleList::Main();
}
// The program produces output similar to the following:
//
// Ordered:
//
// 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, <end>
//
// Scrambled:
//
// 5, 2, 8, 9, 6, 1, 7, 0, 4, 3, <end>
using System;
using System.Collections;
public class ScrambleList : ArrayList
{
public static void Main()
{
// Create an empty ArrayList, and add some elements.
ScrambleList integerList = new ScrambleList();
for (int i = 0; i < 10; i++)
{
integerList.Add(i);
}
Console.WriteLine("Ordered:\n");
foreach (int value in integerList)
{
Console.Write("{0}, ", value);
}
Console.WriteLine("<end>\n\nScrambled:\n");
// Scramble the order of the items in the list.
integerList.Scramble();
foreach (int value in integerList)
{
Console.Write("{0}, ", value);
}
Console.WriteLine("<end>\n");
}
public void Scramble()
{
int limit = this.Count;
int temp;
int swapindex;
Random rnd = new Random();
for (int i = 0; i < limit; i++)
{
// The Item property of ArrayList is the default indexer. Thus,
// this[i] is used instead of Item[i].
temp = (int)this[i];
swapindex = rnd.Next(0, limit - 1);
this[i] = this[swapindex];
this[swapindex] = temp;
}
}
}
// The program produces output similar to the following:
//
// Ordered:
//
// 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, <end>
//
// Scrambled:
//
// 5, 2, 8, 9, 6, 1, 7, 0, 4, 3, <end>
Imports System.Collections
Public Class ScrambleList
Inherits ArrayList
Public Shared Sub Main()
' Create an empty ArrayList, and add some elements.
Dim integerList As New ScrambleList()
For i As Integer = 0 To 9
integerList.Add(i)
Next i
Console.WriteLine("Ordered:" + Environment.NewLine)
For Each value As Integer In integerList
Console.Write("{0}, ", value)
Next value
Console.WriteLine("<end>" + Environment.NewLine + Environment.NewLine + "Scrambled:" + Environment.NewLine)
' Scramble the order of the items in the list.
integerList.Scramble()
For Each value As Integer In integerList
Console.Write("{0}, ", value)
Next value
Console.WriteLine("<end>" + Environment.NewLine)
End Sub
Public Sub Scramble()
Dim limit As Integer = MyClass.Count
Dim temp As Integer
Dim swapindex As Integer
Dim rnd As New Random()
For i As Integer = 0 To limit - 1
' The Item property of ArrayList is the default indexer. Thus,
' Me(i) and MyClass.Item(i) are used interchangeably.
temp = CType(Me(i), Integer)
swapindex = rnd.Next(0, limit - 1)
MyClass.Item(i) = Me(swapindex)
MyClass.Item(swapindex) = temp
Next i
End Sub
End Class
' The program produces output similar to the following:
'
' Ordered:
'
' 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, <end>
'
' Scrambled:
'
' 5, 2, 8, 9, 6, 1, 7, 0, 4, 3, <end>
Remarques
Retourne Item[] un Object, vous devrez peut-être convertir la valeur retournée en type d’origine afin de la manipuler. Il est important de noter que n’est ArrayList pas une collection fortement typée. Pour obtenir une alternative fortement typée, consultez List<T>.
ArrayList accepte null comme valeur valide et autorise les éléments en double.
Cette propriété permet d'accéder à un élément spécifique dans la collection à l'aide de la syntaxe suivante : myCollection[index].
Le langage C# utilise le mot clé this pour définir les indexeurs au lieu d'implémenter la propriété Item[]. Visual Basic implémente Item[] comme propriété par défaut, ce qui fournit les mêmes fonctionnalités d'indexation.
La récupération de la valeur de cette propriété est une O(1) opération ; la définition de la propriété est également une O(1) opération.
S’applique à
Voir aussi
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