ArrayList.Item[Int32] Propriété

Définition

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, set
Default Public Overridable Property Item(index As Integer) As Object

Paramètres

index
Int32

Index de base zéro de l'élément à obtenir ou à définir.

Valeur de propriété

Object

Élément au niveau de l'index spécifié.

Implémente

Exceptions

index est inférieur à zéro.

  • ou - index est supérieur ou égal à Count.

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 assignant 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 la Item[] propriété explicitement pour assigner 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

Le Item[] retourne un. Object par conséquent, vous devrez peut-être effectuer un cast de la valeur retournée vers le type d’origine pour pouvoir la manipuler. Il est important de noter que ArrayList n’est 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 this mot clé pour définir les indexeurs au lieu d’implémenter la Item[] propriété. 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