IEnumerable 介面

  • 參考

定義

命名空間:
System.Collections
組件:
System.Runtime.dll
組件:
mscorlib.dll
組件:
netstandard.dll

公開能逐一查看非泛型集合內容一次的列舉程式。

public interface class IEnumerable
public interface IEnumerable
[System.Runtime.InteropServices.Guid("496B0ABE-CDEE-11d3-88E8-00902754C43A")]
public interface IEnumerable
[System.Runtime.InteropServices.Guid("496B0ABE-CDEE-11d3-88E8-00902754C43A")]
[System.Runtime.InteropServices.ComVisible(true)]
public interface IEnumerable
type IEnumerable = interface
[<System.Runtime.InteropServices.Guid("496B0ABE-CDEE-11d3-88E8-00902754C43A")>]
type IEnumerable = interface
[<System.Runtime.InteropServices.Guid("496B0ABE-CDEE-11d3-88E8-00902754C43A")>]
[<System.Runtime.InteropServices.ComVisible(true)>]
type IEnumerable = interface
Public Interface IEnumerable
衍生
屬性
GuidAttribute ComVisibleAttribute

範例

下列程式代碼範例示範藉由實 IEnumerable 作 和 IEnumerator 介面來逐一查看自定義集合的最佳做法。 在此範例中，不會明確呼叫這些介面的成員，但會實作這些介面，以支援 foreach 在Visual Basic中使用 (For Each) 逐一查看集合。 此範例是完整的控制台應用程式。 若要編譯 Visual Basic 應用程式，請在專案的 [屬性] 頁面中，將 Startup 物件變更為 Sub Main。

using System;
using System.Collections;

// Simple business object.
public class Person
{
    public Person(string fName, string lName)
    {
        this.firstName = fName;
        this.lastName = lName;
    }

    public string firstName;
    public string lastName;
}

// Collection of Person objects. This class
// implements IEnumerable so that it can be used
// with ForEach syntax.
public class People : IEnumerable
{
    private Person[] _people;
    public People(Person[] pArray)
    {
        _people = new Person[pArray.Length];

        for (int i = 0; i < pArray.Length; i++)
        {
            _people[i] = pArray[i];
        }
    }

// Implementation for the GetEnumerator method.
    IEnumerator IEnumerable.GetEnumerator()
    {
       return (IEnumerator) GetEnumerator();
    }

    public PeopleEnum GetEnumerator()
    {
        return new PeopleEnum(_people);
    }
}

// When you implement IEnumerable, you must also implement IEnumerator.
public class PeopleEnum : IEnumerator
{
    public Person[] _people;

    // Enumerators are positioned before the first element
    // until the first MoveNext() call.
    int position = -1;

    public PeopleEnum(Person[] list)
    {
        _people = list;
    }

    public bool MoveNext()
    {
        position++;
        return (position < _people.Length);
    }

    public void Reset()
    {
        position = -1;
    }

    object IEnumerator.Current
    {
        get
        {
            return Current;
        }
    }

    public Person Current
    {
        get
        {
            try
            {
                return _people[position];
            }
            catch (IndexOutOfRangeException)
            {
                throw new InvalidOperationException();
            }
        }
    }
}

class App
{
    static void Main()
    {
        Person[] peopleArray = new Person[3]
        {
            new Person("John", "Smith"),
            new Person("Jim", "Johnson"),
            new Person("Sue", "Rabon"),
        };

        People peopleList = new People(peopleArray);
        foreach (Person p in peopleList)
            Console.WriteLine(p.firstName + " " + p.lastName);
    }
}

/* This code produces output similar to the following:
 *
 * John Smith
 * Jim Johnson
 * Sue Rabon
 *
 */

Imports System.Collections

' Simple business object.
Public Class Person

    Public Sub New(ByVal fName As String, ByVal lName As String)
        Me.firstName = fName
        Me.lastName = lName
    End Sub


    Public firstName As String
    Public lastName As String
End Class

' Collection of Person objects, which implements IEnumerable so that
' it can be used with ForEach syntax.
Public Class People
    Implements IEnumerable

    Private _people() As Person

    Public Sub New(ByVal pArray() As Person)
        _people = New Person(pArray.Length - 1) {}

        Dim i As Integer
        For i = 0 To pArray.Length - 1
            _people(i) = pArray(i)
        Next i
    End Sub

    ' Implementation of GetEnumerator.
    Public Function GetEnumerator() As IEnumerator _
      Implements IEnumerable.GetEnumerator

        Return New PeopleEnum(_people)
    End Function

End Class

' When you implement IEnumerable, you must also implement IEnumerator.
Public Class PeopleEnum
    Implements IEnumerator

    Public _people() As Person

    ' Enumerators are positioned before the first element
    ' until the first MoveNext() call.
    Dim position As Integer = -1

    Public Sub New(ByVal list() As Person)
        _people = list
    End Sub

    Public Function MoveNext() As Boolean Implements IEnumerator.MoveNext
        position = position + 1
        Return (position < _people.Length)
    End Function

    Public Sub Reset() Implements IEnumerator.Reset
        position = -1
    End Sub

    Public ReadOnly Property Current() As Object Implements IEnumerator.Current
        Get
            Try
                Return _people(position)
            Catch ex As IndexOutOfRangeException
                Throw New InvalidOperationException()
            End Try
        End Get
    End Property
End Class

Class App
    Shared Sub Main()
        Dim peopleArray() As Person = { _
            New Person("John", "Smith"), _
            New Person("Jim", "Johnson"), _
            New Person("Sue", "Rabon")}

        Dim peopleList As New People(peopleArray)
        Dim p As Person
        For Each p In peopleList
            Console.WriteLine(p.firstName + " " + p.lastName)
        Next

    End Sub
End Class

' This code produces output similar to the following:
' 
' John Smith
' Jim Johnson
' Sue Rabon

備註

IEnumerable 是可列舉之所有非泛型集合的基底介面。 如需此介面的泛型版本，請參閱 System.Collections.Generic.IEnumerable<T>。 IEnumerable 包含單一方法， GetEnumerator這個方法會傳 IEnumerator回 。 IEnumerator藉由公開 屬性和 方法MoveNextReset，提供逐一Current查看集合的能力。

最佳做法是在集合類別上實 IEnumerable 作 和 IEnumerator ，以在Visual Basic) 語法中啟用 foreach (For Each ，但不需要實作 IEnumerable 。 如果您的集合未實 IEnumerable作 ，您仍必須遵循反覆運算器模式來支援此語法，方法是提供 GetEnumerator 傳回介面、類別或結構的方法。 使用 Visual Basic 時，您必須提供 IEnumerator 由 傳 GetEnumerator回的實作。 使用 C# 進行開發時，您必須提供類別，其中包含 Current 屬性和 ResetMoveNext 方法，如 所述IEnumerator，但類別不需要實IEnumerator作 。

方法

GetEnumerator()

傳回逐一查看集合的列舉值。

擴充方法

Cast<TResult>(IEnumerable)

將 IEnumerable 的項目轉換成指定的型別。
OfType<TResult>(IEnumerable)

根據指定的型別來篩選 IEnumerable 的項目。
AsParallel(IEnumerable)

啟用查詢的平行化作業。
AsQueryable(IEnumerable)

將 IEnumerable 轉換成 IQueryable。

適用於

另請參閱