ReadOnlyCollectionBase.GetEnumerator メソッド

.NET Framework クラス ライブラリ リファレンス

ReadOnlyCollectionBase.GetEnumerator メソッド

ReadOnlyCollectionBase インスタンスを反復処理する列挙子を返します。

名前空間: System.Collections
アセンブリ: mscorlib (mscorlib.dll 内)
構文

Visual Basic (宣言)

Public Overridable Function
 GetEnumerator As IEnumerator

Visual Basic (使用法)

Dim instance As ReadOnlyCollectionBase
Dim returnValue As IEnumerator

returnValue = instance.GetEnumerator

C#

public virtual IEnumerator GetEnumerator ()

C++

public:
virtual IEnumerator^ GetEnumerator ()

J#

public IEnumerator GetEnumerator ()

JScript

public function GetEnumerator () : IEnumerator

戻り値
ReadOnlyCollectionBase インスタンスの IEnumerator。

解説

C# 言語の foreach ステートメント (Visual Basic の場合は for each) を使用することで列挙子の複雑さを回避できます。したがって、列挙子を直接操作するのではなく、foreach の使用をお勧めします。

列挙子を使用すると、コレクション内のデータを読み取ることができますが、基になるコレクションを変更することはできません。

初期状態では、列挙子はコレクションの最初の要素の前に位置しています。Reset を実行した場合も、列挙子はこの位置に戻されます。この位置で、Current が未定義です。したがって、Current の値を読み取る前に、MoveNext を呼び出して、コレクションの最初の要素に列挙子を進める必要があります。

Current は、MoveNext または Reset が呼び出されるまでは同じオブジェクトを返します。MoveNext は、Current を次の要素に設定します。

MoveNext がコレクションの末尾を過ぎると、列挙子はコレクションの最後の要素の後ろに配置され、MoveNext は false を返します。列挙子がこの位置にある場合、以降、MoveNext を呼び出しても false が返されます。MoveNext への最後の呼び出しで false が返された場合は、Current が未定義です。Current をコレクションの最初の要素に再び設定するには、Reset を呼び出してから、MoveNext を呼び出します。

列挙子は、コレクションが変更されない限り有効です。要素の追加、変更、削除などの変更がコレクションに対して実行されると、列挙子は回復不可能な無効状態になり、動作は未定義になります。

列挙子はコレクションへの排他アクセス権を持たないため、コレクションの列挙処理は、本質的にはスレッド セーフな処理ではありません。すべての列挙処理が終わるまでコレクションをロックすることにより、列挙処理でのスレッド セーフを確保できます。コレクションに対し複数のスレッドがアクセスして読み取りや書き込みを行うことができるようにするには、独自に同期化を実装する必要があります。

このメソッドは O(1) 操作です。

使用例

ReadOnlyCollectionBase クラスを実装するコード例を次に示します。

Visual Basic

Imports System
Imports System.Collections

Public Class ROCollection
    Inherits ReadOnlyCollectionBase


    Public Sub New(sourceList
 As IList)
        InnerList.AddRange(sourceList)
    End Sub 'New


    Default Public ReadOnly
 Property Item(index As Integer)
 As [Object]
        Get
            Return InnerList(index)
        End Get
    End Property


    Public Function IndexOf(value As
 [Object]) As Integer
        Return InnerList.IndexOf(value)
    End Function 'IndexOf


    Public Function Contains(value As
 [Object]) As Boolean
        Return InnerList.Contains(value)
    End Function 'Contains

End Class 'ROCollection 


Public Class SamplesCollectionBase

    Public Shared Sub Main()

        ' Create an ArrayList.
        Dim myAL As New
 ArrayList()
        myAL.Add("red")
        myAL.Add("blue")
        myAL.Add("yellow")
        myAL.Add("green")
        myAL.Add("orange")
        myAL.Add("purple")

        ' Create a new ROCollection that contains the elements in myAL.
        Dim myCol As New
 ROCollection(myAL)

        ' Display the contents of the collection using For Each. This
 is the preferred method.
        Console.WriteLine("Contents of the collection (using For
 Each):")
        PrintValues1(myCol)

        ' Display the contents of the collection using the enumerator.
        Console.WriteLine("Contents of the collection (using enumerator):")
        PrintValues2(myCol)

        ' Display the contents of the collection using the Count property
 and the Item property.
        Console.WriteLine("Contents of the collection (using Count
 and Item):")
        PrintIndexAndValues(myCol)

        ' Search the collection with Contains and IndexOf.
        Console.WriteLine("Contains yellow: {0}",
 myCol.Contains("yellow"))
        Console.WriteLine("orange is at index {0}.",
 myCol.IndexOf("orange"))
        Console.WriteLine()

    End Sub 'Main


    ' Uses the Count property and the Item property.
    Public Shared Sub PrintIndexAndValues(myCol
 As ROCollection)
        Dim i As Integer
        For i = 0 To myCol.Count - 1
            Console.WriteLine("   [{0}]:   {1}", i,
 myCol(i))
        Next i
        Console.WriteLine()
    End Sub 'PrintIndexAndValues


    ' Uses the For Each statement which hides the complexity of the
 enumerator.
    ' NOTE: The For Each statement is the preferred way of enumerating
 the contents of a collection.
    Public Shared Sub PrintValues1(myCol
 As ROCollection)
        Dim obj As [Object]
        For Each obj In
  myCol
            Console.WriteLine("   {0}", obj)
        Next obj
        Console.WriteLine()
    End Sub 'PrintValues1


    ' Uses the enumerator. 
    ' NOTE: The For Each statement is the preferred way of enumerating
 the contents of a collection.
    Public Shared Sub PrintValues2(myCol
 As ROCollection)
        Dim myEnumerator As System.Collections.IEnumerator
 = myCol.GetEnumerator()
        While myEnumerator.MoveNext()
            Console.WriteLine("   {0}", myEnumerator.Current)
        End While
        Console.WriteLine()
    End Sub 'PrintValues2

End Class 'SamplesCollectionBase
 


'This code produces the following output.
'
'Contents of the collection (using For Each):
'   red
'   blue
'   yellow
'   green
'   orange
'   purple
'
'Contents of the collection (using enumerator):
'   red
'   blue
'   yellow
'   green
'   orange
'   purple
'
'Contents of the collection (using Count and Item):
'   [0]:   red
'   [1]:   blue
'   [2]:   yellow
'   [3]:   green
'   [4]:   orange
'   [5]:   purple
'
'Contains yellow: True
'orange is at index 4.

C#

using System;
using System.Collections;

public class ROCollection : ReadOnlyCollectionBase
  {

   public ROCollection( IList sourceList )  {
      InnerList.AddRange( sourceList );
   }

   public Object this[ int
 index ]  {
      get  {
         return( InnerList[index] );
      }
   }

   public int IndexOf( Object value )  {
      return( InnerList.IndexOf( value ) );
   }

   public bool Contains( Object value )  {
      return( InnerList.Contains( value ) );
   }

}


public class SamplesCollectionBase  {

   public static void Main()
  {

      // Create an ArrayList.
      ArrayList myAL = new ArrayList();
      myAL.Add( "red" );
      myAL.Add( "blue" );
      myAL.Add( "yellow" );
      myAL.Add( "green" );
      myAL.Add( "orange" );
      myAL.Add( "purple" );
 
      // Create a new ROCollection that contains the elements in myAL.
      ROCollection myCol = new ROCollection( myAL );

      // Display the contents of the collection using foreach. This
 is the preferred method.
      Console.WriteLine( "Contents of the collection (using
 foreach):" );
      PrintValues1( myCol );

      // Display the contents of the collection using the enumerator.
      Console.WriteLine( "Contents of the collection (using
 enumerator):" );
      PrintValues2( myCol );

      // Display the contents of the collection using the Count property
 and the Item property.
      Console.WriteLine( "Contents of the collection (using
 Count and Item):" );
      PrintIndexAndValues( myCol );

      // Search the collection with Contains and IndexOf.
      Console.WriteLine( "Contains yellow: {0}", myCol.Contains( "yellow"
 ) );
      Console.WriteLine( "orange is at index {0}.", myCol.IndexOf( "orange"
 ) );
      Console.WriteLine();

   }
 
   // Uses the Count property and the Item property.
   public static void PrintIndexAndValues(
 ROCollection myCol )  {
      for ( int i = 0; i < myCol.Count;
 i++ )
         Console.WriteLine( "   [{0}]:   {1}", i, myCol[i] );
      Console.WriteLine();
   }

   // Uses the foreach statement which hides the complexity of the enumerator.
   // NOTE: The foreach statement is the preferred way of enumerating
 the contents of a collection.
   public static void PrintValues1(
 ROCollection myCol )  {
      foreach ( Object obj in myCol )
         Console.WriteLine( "   {0}", obj );
      Console.WriteLine();
   }

   // Uses the enumerator. 
   // NOTE: The foreach statement is the preferred way of enumerating
 the contents of a collection.
   public static void PrintValues2(
 ROCollection myCol )  {
      System.Collections.IEnumerator myEnumerator = myCol.GetEnumerator();
      while ( myEnumerator.MoveNext() )
         Console.WriteLine( "   {0}", myEnumerator.Current );
      Console.WriteLine();
   }

}


/* 
This code produces the following output.

Contents of the collection (using foreach):
   red
   blue
   yellow
   green
   orange
   purple

Contents of the collection (using enumerator):
   red
   blue
   yellow
   green
   orange
   purple

Contents of the collection (using Count and Item):
   [0]:   red
   [1]:   blue
   [2]:   yellow
   [3]:   green
   [4]:   orange
   [5]:   purple

Contains yellow: True
orange is at index 4.

*/

C++

using namespace System;
using namespace System::Collections;
public ref class ROCollection: public
 ReadOnlyCollectionBase
{
public:
   ROCollection( IList^ sourceList )
   {
      InnerList->AddRange( sourceList );
   }

   property Object^ Item [int]
   {
      Object^ get( int index )
      {
         return (InnerList[ index ]);
      }

   }
   int IndexOf( Object^ value )
   {
      return (InnerList->IndexOf( value ));
   }

   bool Contains( Object^ value )
   {
      return (InnerList->Contains( value ));
   }

};

void PrintIndexAndValues( ROCollection^ myCol );
void PrintValues2( ROCollection^ myCol );
int main()
{
   // Create an ArrayList.
   ArrayList^ myAL = gcnew ArrayList;
   myAL->Add( "red" );
   myAL->Add( "blue" );
   myAL->Add( "yellow" );
   myAL->Add( "green" );
   myAL->Add( "orange" );
   myAL->Add( "purple" );

   // Create a new ROCollection that contains the elements in myAL.
   ROCollection^ myCol = gcnew ROCollection( myAL );

   // Display the contents of the collection using the enumerator.
   Console::WriteLine( "Contents of the collection (using
 enumerator):" );
   PrintValues2( myCol );

   // Display the contents of the collection using the Count property
 and the Item property.
   Console::WriteLine( "Contents of the collection (using
 Count and Item):" );
   PrintIndexAndValues( myCol );

   // Search the collection with Contains and IndexOf.
   Console::WriteLine( "Contains yellow: {0}", myCol->Contains( "yellow"
 ) );
   Console::WriteLine( "orange is at index {0}.", myCol->IndexOf( "orange"
 ) );
   Console::WriteLine();
}


// Uses the Count property and the Item property.
void PrintIndexAndValues( ROCollection^ myCol )
{
   for ( int i = 0; i < myCol->Count;
 i++ )
      Console::WriteLine( "   [{0}]:   {1}", i, myCol->Item[ i ] );
   Console::WriteLine();
}


// Uses the enumerator. 
void PrintValues2( ROCollection^ myCol )
{
   System::Collections::IEnumerator^ myEnumerator = myCol->GetEnumerator();
   while ( myEnumerator->MoveNext() )
      Console::WriteLine( "   {0}", myEnumerator->Current );

   Console::WriteLine();
}

/* 
This code produces the following output.

Contents of the collection (using enumerator):
   red
   blue
   yellow
   green
   orange
   purple

Contents of the collection (using Count and Item):
   [0]:   red
   [1]:   blue
   [2]:   yellow
   [3]:   green
   [4]:   orange
   [5]:   purple

Contains yellow: True
orange is at index 4.

*/

J#

import System.*;
import System.Collections.*;

public class ROCollection extends ReadOnlyCollectionBase
{
    public ROCollection(IList sourceList) 
    {
        get_InnerList().AddRange(sourceList);
    } //ROCollection
   
    /** @property 
     */
    public Object get_Item(int index)
    {
        return get_InnerList().get_Item(index);
    } //get_Item
     
    public int IndexOf(Object value) 
    {
        return get_InnerList().IndexOf(value);
    } //IndexOf
   
    public boolean Contains(Object value) 
    {
        return get_InnerList().Contains(value);
    } //Contains
} //ROCollection

public class SamplesCollectionBase
{
    public static void main(String[]
 args)
    {
        // Create an ArrayList.
        ArrayList myAL = new ArrayList();
        myAL.Add("red");
        myAL.Add("blue");
        myAL.Add("yellow");
        myAL.Add("green");
        myAL.Add("orange");
        myAL.Add("purple");
          
        // Create a new ROCollection that contains the elements in myAL.
        ROCollection myCol = new ROCollection(myAL);
          
        // Display the contents of the collection using for. This is
 the 
        // preferred method.
        Console.WriteLine("Contents of the collection (using
 for):");
        PrintValues1(myCol);
          
        // Display the contents of the collection using the enumerator.
        Console.WriteLine("Contents of the collection (using
 enumerator):");
        PrintValues2(myCol);
          
        // Display the contents of the collection using the Count property
 and 
        // the Item property.
        Console.WriteLine("Contents of the collection (using
 Count and Item):");
        PrintIndexAndValues(myCol);
          
        // Search the collection with Contains and IndexOf.
        Console.WriteLine("Contains yellow: {0}",
            (System.Boolean)myCol.Contains("yellow"));
        Console.WriteLine("orange is at index {0}.", 
            (Int32)myCol.IndexOf("orange"));
        Console.WriteLine();
    } //main
    
    // Uses the Count property and the Item property.
    public static void PrintIndexAndValues(ROCollection
 myCol) 
    {
        for(int i = 0; i < myCol.get_Count();
 i++) {
            Console.WriteLine("   [{0}]:   {1}",(Int32)i, myCol.get_Item(i));
        } 
        Console.WriteLine();
    } //PrintIndexAndValues
   
    // Uses the for statement which hides the complexity of the enumerator.
    // NOTE: The for statement is the preferred way of enumerating the
 contents
    // of a collection.
    public static void PrintValues1(ROCollection
 myCol) 
    {
        for (int iCtr = 0; iCtr < myCol.get_Count();
 iCtr++ ) {
            Object obj = myCol.get_Item(iCtr);
            Console.WriteLine("   {0}", obj);
        }
        Console.WriteLine();
    } //PrintValues1
     
    // Uses the enumerator. 
    // NOTE: The for statement is the preferred way of enumerating the
    // contents of a collection.
    public static void PrintValues2(ROCollection
 myCol) 
    {
        System.Collections.IEnumerator myEnumerator = myCol.GetEnumerator();
        while(myEnumerator.MoveNext()) {
            Console.WriteLine("   {0}", myEnumerator.get_Current());
        }
        Console.WriteLine();
    } //PrintValues2
} //SamplesCollectionBase
 
/* 
This code produces the following output.

Contents of the collection (using for):
   red
   blue
   yellow
   green
   orange
   purple

Contents of the collection (using enumerator):
   red
   blue
   yellow
   green
   orange
   purple

Contents of the collection (using Count and Item):
   [0]:   red
   [1]:   blue
   [2]:   yellow
   [3]:   green
   [4]:   orange
   [5]:   purple

Contains yellow: True
orange is at index 4.

*/

プラットフォーム

Windows 98, Windows 2000 SP4, Windows Millennium Edition, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

開発プラットフォームの中には、.NET Framework によってサポートされていないバージョンがあります。サポートされているバージョンについては、「システム要件」を参照してください。

バージョン情報

.NET Framework
サポート対象 : 2.0、1.1、1.0

参照

関連項目
ReadOnlyCollectionBase クラス
ReadOnlyCollectionBase メンバ
System.Collections 名前空間
IEnumerator インターフェイス