ArrayList.Item[Int32] Свойство

Определение

Возвращает или задает элемент по указанному индексу.Gets or sets the element at the specified index.

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; }
member this.Item(int) : obj with get, set
Default Public Overridable Property Item(index As Integer) As Object

Параметры

index
Int32

Отсчитываемый от нуля индекс элемента, который требуется возвратить или задать.The zero-based index of the element to get or set.

Значение свойства

Элемент, расположенный по указанному индексу.The element at the specified index.

Реализации

Исключения

Значение параметра index меньше нуля.index is less than zero.

-или--or- Значение параметра index больше или равно значению свойства Count.index is equal to or greater than Count.

Примеры

В следующем примере кода создается ArrayList и добавляется несколько элементов.The following code example creates an ArrayList and adds several items. В примере демонстрируется доступ к элементам со свойством Item[Int32] (индексатор в C#) и изменение элемента путем присвоения нового значения свойству Item[Int32] для указанного индекса.The example demonstrates accessing elements with the Item[Int32] property (the indexer in C#), and changing an element by assigning a new value to the Item[Int32] property for a specified index. В примере также показано, что свойство Item[Int32] не может использоваться для доступа к элементам или их добавления за пределами текущего размера списка.The example also shows that the Item[Int32] property cannot be used to access or add elements outside the current size of the list.

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

В следующем примере явно используется свойство Item[Int32] для присвоения значений элементам в списке.The following example uses the Item[Int32] property explicitly to assign values to items in the list. В примере определяется класс, наследующий ArrayList, и добавляется метод для шифрования элементов списка.The example defines a class that inherits an ArrayList and adds a method to scramble the list items.

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:" + vbNewLine)
        For Each value As Integer In integerList
            Console.Write("{0}, ", value)
        Next value
        Console.WriteLine("<end>" + vbNewLine + vbNewLine + "Scrambled:" + vbNewLine)

        ' 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>" + vbNewLine)
    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>

Комментарии

@No__t-0 возвращает Object, поэтому может потребоваться привести возвращаемое значение к исходному типу, чтобы управлять им.The Item[Int32] returns an Object, so you may need to cast the returned value to the original type in order to manipulate it. Важно отметить, что ArrayList не является строго типизированной коллекцией.It is important to note that ArrayList is not a strongly-typed collection. Сведения о строго типизированной альтернативе см. в разделе List<T>.For a strongly-typed alternative, see List<T>.

ArrayList принимает null как допустимое значение и допускает дублирование элементов.ArrayList accepts null as a valid value and allows duplicate elements.

Это свойство предоставляет доступ к указанному элементу коллекции при использовании следующего синтаксиса: myCollection[index].This property provides the ability to access a specific element in the collection by using the following syntax: myCollection[index].

C# Язык использует ключевое слово this для определения индексаторов вместо реализации свойства Item[Int32].The C# language uses the this keyword to define the indexers instead of implementing the Item[Int32] property. В языке Visual Basic в качестве свойства по умолчанию реализовано свойство Item[Int32], предоставляющее те же возможности индексирования.Visual Basic implements Item[Int32] as a default property, which provides the same indexing functionality.

Получение значения этого свойства является операцией O(1); Задание свойства также является операцией O(1).Retrieving the value of this property is an O(1) operation; setting the property is also an O(1) operation.

Применяется к

Дополнительно