ReadOnlyCollectionBase Classe

Definizione

Fornisce la classe base abstract per una raccolta di sola lettura non generica fortemente tipizzata.Provides the abstract base class for a strongly typed non-generic read-only collection.

public ref class ReadOnlyCollectionBase abstract : System::Collections::ICollection
[System.Runtime.InteropServices.ComVisible(true)]
[System.Serializable]
public abstract class ReadOnlyCollectionBase : System.Collections.ICollection
type ReadOnlyCollectionBase = class
    interface ICollection
    interface IEnumerable
Public MustInherit Class ReadOnlyCollectionBase
Implements ICollection
Ereditarietà
ReadOnlyCollectionBase
Derivato
Attributi
Implementazioni

Esempi

Nell'esempio di codice seguente viene implementata la classe ReadOnlyCollectionBase.The following code example implements the ReadOnlyCollectionBase class.

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.

*/
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.

*/

Imports System.Collections

Public Class ROCollection
    Inherits ReadOnlyCollectionBase


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


    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


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


    ' 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


    ' 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


    ' 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

End Class


'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.

Commenti

Un'istanza ReadOnlyCollectionBase è sempre di sola lettura.A ReadOnlyCollectionBase instance is always read-only. Per una versione modificabile di questa classe, vedere CollectionBase.See CollectionBase for a modifiable version of this class.

Importante

Non è consigliabile usare la classe ReadOnlyCollectionBase per il nuovo sviluppo.We don't recommend that you use the ReadOnlyCollectionBase class for new development. È invece consigliabile usare la classe generica ReadOnlyCollection<T>.Instead, we recommend that you use the generic ReadOnlyCollection<T> class. Per altre informazioni, vedere le raccolte non generiche non devono essere usate in GitHub.For more information, see Non-generic collections shouldn't be used on GitHub.

Note per gli eredi

Questa classe di base viene fornita per semplificare la creazione di una raccolta personalizzata di sola lettura fortemente tipizzata per gli implementatori.This base class is provided to make it easier for implementers to create a strongly typed read-only custom collection. Gli implementatori sono invitati a estendere questa classe di base invece di crearne di propri.Implementers are encouraged to extend this base class instead of creating their own. I membri di questa classe di base sono protetti e sono destinati a essere utilizzati solo tramite una classe derivata.Members of this base class are protected and are intended to be used through a derived class only.

Questa classe rende disponibile la raccolta sottostante tramite la proprietà InnerList, che deve essere utilizzata solo dalle classi derivate direttamente da ReadOnlyCollectionBase.This class makes the underlying collection available through the InnerList property, which is intended for use only by classes that are derived directly from ReadOnlyCollectionBase. La classe derivata deve garantire che i propri utenti non possano modificare la raccolta sottostante.The derived class must ensure that its own users cannot modify the underlying collection.

Costruttori

ReadOnlyCollectionBase()

Inizializza una nuova istanza della classe ReadOnlyCollectionBase.Initializes a new instance of the ReadOnlyCollectionBase class.

Proprietà

Count

Ottiene il numero di elementi contenuti nell'istanza di ReadOnlyCollectionBase.Gets the number of elements contained in the ReadOnlyCollectionBase instance.

InnerList

Ottiene l'elenco degli elementi contenuti nell'istanza di ReadOnlyCollectionBase.Gets the list of elements contained in the ReadOnlyCollectionBase instance.

Metodi

Equals(Object)

Determina se l'oggetto specificato è uguale all'oggetto corrente.Determines whether the specified object is equal to the current object.

(Ereditato da Object)
GetEnumerator()

Restituisce un enumeratore per lo scorrimento dell'istanza di ReadOnlyCollectionBase.Returns an enumerator that iterates through the ReadOnlyCollectionBase instance.

GetHashCode()

Funge da funzione hash predefinita.Serves as the default hash function.

(Ereditato da Object)
GetType()

Ottiene l'oggetto Type dell'istanza corrente.Gets the Type of the current instance.

(Ereditato da Object)
MemberwiseClone()

Crea una copia superficiale dell'oggetto Object corrente.Creates a shallow copy of the current Object.

(Ereditato da Object)
ToString()

Restituisce una stringa che rappresenta l'oggetto corrente.Returns a string that represents the current object.

(Ereditato da Object)

Implementazioni dell'interfaccia esplicita

ICollection.CopyTo(Array, Int32)

Copia l'intero oggetto ReadOnlyCollectionBase in un oggetto Array compatibile unidimensionale, a partire dall'indice specificato della matrice di destinazione.Copies the entire ReadOnlyCollectionBase to a compatible one-dimensional Array, starting at the specified index of the target array.

ICollection.IsSynchronized

Ottiene un valore che indica se l'accesso a un oggetto ReadOnlyCollectionBase è sincronizzato (thread-safe).Gets a value indicating whether access to a ReadOnlyCollectionBase object is synchronized (thread safe).

ICollection.SyncRoot

Ottiene un oggetto che può essere usato per sincronizzare l'accesso all'oggetto ReadOnlyCollectionBase.Gets an object that can be used to synchronize access to a ReadOnlyCollectionBase object.

Metodi di estensione

Cast<TResult>(IEnumerable)

Esegue il cast degli elementi di un oggetto IEnumerable nel tipo specificato.Casts the elements of an IEnumerable to the specified type.

OfType<TResult>(IEnumerable)

Filtra gli elementi di un oggetto IEnumerable in base a un tipo specificato.Filters the elements of an IEnumerable based on a specified type.

AsParallel(IEnumerable)

Consente la parallelizzazione di una query.Enables parallelization of a query.

AsQueryable(IEnumerable)

Converte un oggetto IEnumerable in un oggetto IQueryable.Converts an IEnumerable to an IQueryable.

Si applica a

Thread safety

I membri statici pubblici (Shared in Visual Basic) di questo tipo sono thread-safe.Public static (Shared in Visual Basic) members of this type are thread safe. I membri di istanza non sono garantiti come thread-safe.Any instance members are not guaranteed to be thread safe.

Questa implementazione non fornisce un wrapper sincronizzato (thread-safe) per un ReadOnlyCollectionBase, ma le classi derivate possono creare le proprie versioni sincronizzate del ReadOnlyCollectionBase usando la proprietà SyncRoot.This implementation does not provide a synchronized (thread safe) wrapper for a ReadOnlyCollectionBase, but derived classes can create their own synchronized versions of the ReadOnlyCollectionBase using the SyncRoot property.

L'enumerazione di una raccolta non è di per sé una procedura thread-safe.Enumerating through a collection is intrinsically not a thread-safe procedure. Anche se una raccolta è sincronizzata, è possibile che venga modificata da altri thread, con conseguente generazione di un'eccezione da parte dell'enumeratore.Even when a collection is synchronized, other threads can still modify the collection, which causes the enumerator to throw an exception. Per garantire la protezione dei thread durante l'enumerazione, è possibile bloccare la raccolta per l'intera enumerazione oppure intercettare le eccezioni determinate dalle modifiche apportate da altri thread.To guarantee thread safety during enumeration, you can either lock the collection during the entire enumeration or catch the exceptions resulting from changes made by other threads.

Vedi anche