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ArrayList.Item[Int32] Properti

Definisi

Mendapatkan atau mengatur elemen pada indeks yang ditentukan.

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

Parameter

index
Int32

Indeks berbasis nol dari elemen untuk mendapatkan atau mengatur.

Nilai Properti

Elemen pada indeks yang ditentukan.

Penerapan

Pengecualian

index kurang dari nol.

-atau-

index sama dengan atau lebih besar dari Count.

Contoh

Contoh kode berikut membuat ArrayList dan menambahkan beberapa item. Contoh menunjukkan mengakses elemen dengan Item[] properti (pengindeks di C#), dan mengubah elemen dengan menetapkan nilai baru ke Item[] properti untuk indeks tertentu. Contoh juga menunjukkan bahwa Item[] properti tidak dapat digunakan untuk mengakses atau menambahkan elemen di luar ukuran daftar saat ini.

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

Contoh berikut menggunakan Item[] properti secara eksplisit untuk menetapkan nilai ke item dalam daftar. Contoh menentukan kelas yang mewarisi ArrayList dan menambahkan metode untuk mengacak item daftar.

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>

Keterangan

mengembalikan Item[]Object, sehingga Anda mungkin perlu mentransmisikan nilai yang dikembalikan ke jenis asli untuk memanipulasinya. Penting untuk dicatat bahwa ArrayList ini bukan koleksi yang ditik dengan kuat. Untuk alternatif yang dititik dengan kuat, lihat List<T>.

ArrayListnull menerima sebagai nilai yang valid dan memungkinkan elemen duplikat.

Properti ini menyediakan kemampuan untuk mengakses elemen tertentu dalam koleksi dengan menggunakan sintaks berikut: myCollection[index].

Bahasa C# menggunakan this kata kunci untuk menentukan pengindeks alih-alih mengimplementasikan Item[] properti . Visual Basic mengimplementasikan Item[] sebagai properti default, yang menyediakan fungsionalitas pengindeksan yang sama.

Mengambil nilai properti ini adalah O(1) operasi; mengatur properti juga merupakan O(1) operasi.

Berlaku untuk

Lihat juga