ArrayList.IsReadOnly Propriété

Définition

Obtient une valeur indiquant si ArrayList est en lecture seule.

public:
 virtual property bool IsReadOnly { bool get(); };
public virtual bool IsReadOnly { get; }
member this.IsReadOnly : bool
Public Overridable ReadOnly Property IsReadOnly As Boolean

Valeur de propriété

Boolean

true si ArrayList est en lecture seule ; sinon, false. La valeur par défaut est false.

Implémente

Exemples

L’exemple de code suivant montre comment créer un wrapper en lecture seule autour d’un ArrayList et comment déterminer si un ArrayList est en lecture seule.

#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

*/
 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

*/
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

End Class


'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

Remarques

Une collection en lecture seule n’autorise pas l’ajout, la suppression ou la modification d’éléments après sa création.

Une collection en lecture seule est simplement une collection avec un wrapper qui empêche la modification de la collection. par conséquent, si des modifications sont apportées à la collection sous-jacente, la collection en lecture seule reflète ces modifications.

La récupération de la valeur de cette propriété est une O(1) opération.

S’applique à

Voir aussi