ArrayList.IsReadOnly プロパティ

.NET Framework クラス ライブラリ リファレンス

ArrayList.IsReadOnly プロパティ

ArrayList が読み取り専用かどうかを示す値を取得します。

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

Visual Basic (宣言)

Public Overridable ReadOnly
 Property IsReadOnly As Boolean

Visual Basic (使用法)

Dim instance As ArrayList
Dim value As Boolean

value = instance.IsReadOnly

C#

public virtual bool IsReadOnly { get;
 }

C++

public:
virtual property bool IsReadOnly {
    bool get ();
}

J#

/** @property */
public boolean get_IsReadOnly ()

JScript

public function get IsReadOnly
 () : boolean

プロパティ値
ArrayList が読み取り専用の場合は true。それ以外の場合は false。既定値は false です。

解説

読み取り専用のコレクションでは、コレクション作成後に要素の追加、削除、または変更はできません。

読み取り専用のコレクションは、コレクションの変更を防ぐラッパーがコレクションに組み込まれているに過ぎません。したがって、基になっているコレクションで変更が加えられた場合、読み取り専用のコレクションでもその内容が反映されます。

このプロパティ値を取得することは、O(1) 操作になります。

使用例

ArrayList をラップする読み取り専用のラッパーを作成する方法、および ArrayList が読み取り専用かどうかを確認する方法を次のコード例に示します。

Visual Basic

Imports System
Imports System.Collections

Public Class SamplesArrayList

   Public Shared Sub Main()

      Dim myStr As [String]

      ' Creates and initializes a new ArrayList.
      Dim myAL As New ArrayList()
      myAL.Add("red")
      myAL.Add("orange")
      myAL.Add("yellow")

      ' Creates a read-only copy of the ArrayList.
      Dim myReadOnlyAL As ArrayList = ArrayList.ReadOnly(myAL)

      ' Displays whether the ArrayList is read-only or writable.
      If myAL.IsReadOnly Then
         Console.WriteLine("myAL is read-only.")
      Else
         Console.WriteLine("myAL is writable.")
      End If
      If myReadOnlyAL.IsReadOnly Then
         Console.WriteLine("myReadOnlyAL is read-only.")
      Else
         Console.WriteLine("myReadOnlyAL is writable.")
      End If

      ' Displays the contents of both collections.
      Console.WriteLine()
      Console.WriteLine("Initially,")
      Console.WriteLine("The original ArrayList myAL contains:")
      For Each myStr In
  myAL
         Console.WriteLine("   {0}", myStr)
      Next myStr
      Console.WriteLine("The read-only ArrayList myReadOnlyAL
 contains:")
      For Each myStr In
  myReadOnlyAL
         Console.WriteLine("   {0}", myStr)
      Next myStr 

      ' Adding an element to a read-only ArrayList throws an exception.
      Console.WriteLine()
      Console.WriteLine("Trying to add a new element to the read-only
 ArrayList:")
      Try
         myReadOnlyAL.Add("green")
      Catch myException As Exception
         Console.WriteLine(("Exception: " + myException.ToString()))
      End Try

      ' Adding an element to the original ArrayList affects the read-only
 ArrayList.
      myAL.Add("blue")

      ' Displays the contents of both collections again.
      Console.WriteLine()
      Console.WriteLine("After adding a new element to the original
 ArrayList,")
      Console.WriteLine("The original ArrayList myAL contains:")
      For Each myStr In
  myAL
         Console.WriteLine("   {0}", myStr)
      Next myStr
      Console.WriteLine("The read-only ArrayList myReadOnlyAL
 contains:")
      For Each myStr In
  myReadOnlyAL
         Console.WriteLine("   {0}", myStr)
      Next myStr 

   End Sub 'Main

End Class 'SamplesArrayList 


'This code produces the following output.
'
'myAL is writable.
'myReadOnlyAL is read-only.
'
'Initially,
'The original ArrayList myAL contains:
'   red
'   orange
'   yellow
'The read-only ArrayList myReadOnlyAL contains:
'   red
'   orange
'   yellow
'
'Trying to add a new element to the read-only ArrayList:
'Exception: System.NotSupportedException: Collection is read-only.
'   at System.Collections.ReadOnlyArrayList.Add(Object obj)
'   at SamplesArrayList.Main()
'
'After adding a new element to the original ArrayList,
'The original ArrayList myAL contains:
'   red
'   orange
'   yellow
'   blue
'The read-only ArrayList myReadOnlyAL contains:
'   red
'   orange
'   yellow
'   blue

C#

 using System;
 using System.Collections;
 public class SamplesArrayList  {
 
    public static void Main()
  {
 
       // Creates and initializes a new ArrayList.
       ArrayList myAL = new ArrayList();
       myAL.Add( "red" );
       myAL.Add( "orange" );
       myAL.Add( "yellow" );
 
       // Creates a read-only copy of the ArrayList.
       ArrayList myReadOnlyAL = ArrayList.ReadOnly( myAL );
 
       // Displays whether the ArrayList is read-only or writable.
       Console.WriteLine( "myAL is {0}.", myAL.IsReadOnly ? "read-only"
 : "writable" );
       Console.WriteLine( "myReadOnlyAL is {0}.", myReadOnlyAL.IsReadOnly
 ? "read-only" : "writable" );
 
       // Displays the contents of both collections.
       Console.WriteLine( "\nInitially," );
       Console.WriteLine( "The original ArrayList myAL contains:" );
       foreach ( String myStr in myAL )
          Console.WriteLine( "   {0}", myStr );
       Console.WriteLine( "The read-only ArrayList myReadOnlyAL contains:"
 );
       foreach ( String myStr in myReadOnlyAL
 )
          Console.WriteLine( "   {0}", myStr );

       // Adding an element to a read-only ArrayList throws an exception.
       Console.WriteLine( "\nTrying to add a new element
 to the read-only ArrayList:" );
       try  {
          myReadOnlyAL.Add("green");
       } catch ( Exception myException )  {
          Console.WriteLine("Exception: " + myException.ToString());
       }

       // Adding an element to the original ArrayList affects the read-only
 ArrayList.
       myAL.Add( "blue" );

       // Displays the contents of both collections again.
       Console.WriteLine( "\nAfter adding a new element to
 the original ArrayList," );
       Console.WriteLine( "The original ArrayList myAL contains:" );
       foreach ( String myStr in myAL )
          Console.WriteLine( "   {0}", myStr );
       Console.WriteLine( "The read-only ArrayList myReadOnlyAL contains:"
 );
       foreach ( String myStr in myReadOnlyAL
 )
          Console.WriteLine( "   {0}", myStr );

    }

 }


/* 
This code produces the following output.

myAL is writable.
myReadOnlyAL is read-only.

Initially,
The original ArrayList myAL contains:
   red
   orange
   yellow
The read-only ArrayList myReadOnlyAL contains:
   red
   orange
   yellow

Trying to add a new element to the read-only ArrayList:
Exception: System.NotSupportedException: Collection is read-only.
   at System.Collections.ReadOnlyArrayList.Add(Object obj)
   at SamplesArrayList.Main()

After adding a new element to the original ArrayList,
The original ArrayList myAL contains:
   red
   orange
   yellow
   blue
The read-only ArrayList myReadOnlyAL contains:
   red
   orange
   yellow
   blue

*/

C++

#using <system.dll>

using namespace System;
using namespace System::Collections;
int main()
{
   
   // Creates and initializes a new ArrayList.
   ArrayList^ myAL = gcnew ArrayList;
   myAL->Add( "red" );
   myAL->Add( "orange" );
   myAL->Add( "yellow" );
   
   // Creates a read-only copy of the ArrayList.
   ArrayList^ myReadOnlyAL = ArrayList::ReadOnly( myAL );
   
   // Displays whether the ArrayList is read-only or writable.
   Console::WriteLine( "myAL is {0}.", myAL->IsReadOnly ? (String^)"read-only"
 : "writable" );
   Console::WriteLine( "myReadOnlyAL is {0}.", myReadOnlyAL->IsReadOnly
 ? (String^)"read-only" : "writable" );
   
   // Displays the contents of both collections.
   Console::WriteLine( "\nInitially," );
   Console::WriteLine( "The original ArrayList myAL contains:" );
   for ( int i(0); i < myAL->Count; ++i
 )
      Console::WriteLine(  "   {0}", static_cast<String^>(myAL[ i
 ]) );
   Console::WriteLine( "The read-only ArrayList myReadOnlyAL contains:"
 );
   for ( int i(0); i < myReadOnlyAL->Count;
 ++i )
      Console::WriteLine( "   {0}", static_cast<String^>(myReadOnlyAL[
 i ]) );
   
   // Adding an element to a read-only ArrayList throws an exception.
   Console::WriteLine( "\nTrying to add a new element to
 the read-only ArrayList:" );
   try
   {
      myReadOnlyAL->Add( "green" );
   }
   catch ( Exception^ myException ) 
   {
      Console::WriteLine( String::Concat( "Exception: ", myException->ToString()
 ) );
   }

   
   // Adding an element to the original ArrayList affects the read-only
 ArrayList.
   myAL->Add( "blue" );
   
   // Displays the contents of both collections again.
   Console::WriteLine( "\nAfter adding a new element to the
 original ArrayList," );
   Console::WriteLine( "The original ArrayList myAL contains:" );
   for ( int i(0); i < myAL->Count; ++i
 )
      Console::WriteLine( "   {0}", static_cast<String^>(myAL[ i
 ]) );
   Console::WriteLine( "The read-only ArrayList myReadOnlyAL contains:"
 );
   for ( int i(0); i < myReadOnlyAL->Count;
 ++i )
      Console::WriteLine( "   {0}", static_cast<String^>(myReadOnlyAL[
 i ]) );
}

/*
This code produces the following output.

myAL is writable.
myReadOnlyAL is read-only.

Initially,
The original ArrayList myAL contains:
   red
   orange
   yellow
The read-only ArrayList myReadOnlyAL contains:
   red
   orange
   yellow

Trying to add a new element to the read-only ArrayList:
Exception: System.NotSupportedException: Collection is read-only.
   at System.Collections.ReadOnlyArrayList.Add(Object obj)
   at SamplesArrayList.Main()

After adding a new element to the original ArrayList,
The original ArrayList myAL contains:
   red
   orange
   yellow
   blue
The read-only ArrayList myReadOnlyAL contains:
   red
   orange
   yellow
   blue

*/

J#

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

public class SamplesArrayList
{
    public static void main(String[]
 args)
    {
        // Creates and initializes a new ArrayList.
        ArrayList myAL = new ArrayList();

        myAL.Add("red");
        myAL.Add("orange");
        myAL.Add("yellow");

        // Creates a read-only copy of the ArrayList.
        ArrayList myReadOnlyAL = ArrayList.ReadOnly(myAL);

        // Displays whether the ArrayList is read-only or writable.
        Console.WriteLine("myAL is {0}.", myAL.get_IsReadOnly()
            ? "read-only" : "writable");
        Console.WriteLine("myReadOnlyAL is {0}.",myReadOnlyAL.get_IsReadOnly()
            ? "read-only" : "writable");

        // Displays the contents of both collections.
        Console.WriteLine("\nInitially,");
        Console.WriteLine("The original ArrayList myAL contains:");
        for (int iCtr = 0; iCtr < myAL.get_Count();
 iCtr++) {
            String myStr = myAL.get_Item(iCtr).ToString();
            Console.WriteLine("   {0}", myStr);
        }
        Console.WriteLine("The read-only ArrayList myReadOnlyAL contains:");
        for (int iCtr = 0; iCtr < myReadOnlyAL.get_Count();
 iCtr++) {
            String myStr = myReadOnlyAL.get_Item(iCtr).ToString();
            Console.WriteLine("   {0}", myStr);
        }

        // Adding an element to a read-only ArrayList throws an exception.
        Console.WriteLine("\nTrying to add a new element
 to the read-only"
            + " ArrayList:");
        try {
            myReadOnlyAL.Add("green");
        }
        catch (System.Exception myException) {
            Console.WriteLine("Exception: " + myException.ToString());
        }

        // Adding an element to the original ArrayList affects the 
        // read-only ArrayList.
        myAL.Add("blue");

        // Displays the contents of both collections again.
        Console.WriteLine("\nAfter adding a new element "
            + "to the original ArrayList,");
        Console.WriteLine("The original ArrayList myAL contains:");
        for (int iCtr = 0; iCtr < myAL.get_Count();
 iCtr++) {
            String myStr = myAL.get_Item(iCtr).ToString();
            Console.WriteLine("   {0}", myStr);
        }
        Console.WriteLine("The read-only ArrayList myReadOnlyAL contains:");
        for (int iCtr = 0; iCtr < myReadOnlyAL.get_Count();
 iCtr++) {
            String myStr = myReadOnlyAL.get_Item(iCtr).ToString();
            Console.WriteLine("   {0}", myStr);
        }
    } //main 
} //SamplesArrayList

/* 
This code produces the following output.

myAL is writable.
myReadOnlyAL is read-only.

Initially,
The original ArrayList myAL contains:
   red
   orange
   yellow
The read-only ArrayList myReadOnlyAL contains:
   red
   orange
   yellow

Trying to add a new element to the read-only ArrayList:
Exception: System.NotSupportedException: Collection is read-only.
   at System.Collections.ReadOnlyArrayList.Add(Object obj)
   at SamplesArrayList.main(String[] args)

After adding a new element to the original ArrayList,
The original ArrayList myAL contains:
   red
   orange
   yellow
   blue
The read-only ArrayList myReadOnlyAL contains:
   red
   orange
   yellow
   blue

*/

プラットフォーム

Windows 98, Windows 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, 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
.NET Compact Framework
サポート対象 : 2.0、1.0

参照

関連項目
ArrayList クラス
ArrayList メンバ
System.Collections 名前空間
ReadOnly