ArrayList.Item[Int32] Propriedade
Definição
Importante
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Obtém ou define o elemento no índice especificado.
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 ObjectParâmetros
- index
- Int32
O índice com base em zero do elemento a ser obtido ou definido.
Valor da propriedade
O elemento no índice especificado.
Implementações
Exceções
Exemplos
O exemplo de código a seguir cria um ArrayList e adiciona vários itens. O exemplo demonstra como acessar elementos com a Item[] propriedade (o indexador em C#) e alterar um elemento atribuindo um novo valor à Item[] propriedade para um índice especificado. O exemplo também mostra que a Item[] propriedade não pode ser usada para acessar ou adicionar elementos fora do tamanho atual da lista.
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
O exemplo a seguir usa a Item[] propriedade explicitamente para atribuir valores a itens na lista. O exemplo define uma classe que herda um ArrayList e adiciona um método para embaralhar os itens da lista.
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>
Comentários
O Item[] retorna um Object, portanto, talvez seja necessário converter o valor retornado para o tipo original para manipulá-lo. É importante observar que ArrayList não é uma coleção fortemente tipada. Para obter uma alternativa fortemente tipada, consulte List<T>.
ArrayList aceita null como um valor válido e permite elementos duplicados.
Esta propriedade fornece a capacidade de acessar um elemento específico na coleção usando a seguinte sintaxe: myCollection[index].
A linguagem C# usa o this palavra-chave para definir os indexadores em vez de implementar a Item[] propriedade . O Visual Basic implementa Item[] como uma propriedade padrão, que fornece a mesma funcionalidade de indexação.
Recuperar o valor dessa propriedade é uma O(1) operação; definir a propriedade também é uma O(1) operação.
Aplica-se a
Confira também
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