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CollectionBase Class

Definition

Provides the abstract base class for a strongly typed collection.

public abstract class CollectionBase : System.Collections.IList
[System.Serializable]
public abstract class CollectionBase : System.Collections.IList
[System.Serializable]
[System.Runtime.InteropServices.ComVisible(true)]
public abstract class CollectionBase : System.Collections.IList
Inheritance
CollectionBase
Derived
Attributes
Implements

Examples

The following code example implements the CollectionBase class and uses that implementation to create a collection of Int16 objects.

using System;
using System.Collections;

public class Int16Collection : CollectionBase  {

   public Int16 this[ int index ]  {
      get  {
         return( (Int16) List[index] );
      }
      set  {
         List[index] = value;
      }
   }

   public int Add( Int16 value )  {
      return( List.Add( value ) );
   }

   public int IndexOf( Int16 value )  {
      return( List.IndexOf( value ) );
   }

   public void Insert( int index, Int16 value )  {
      List.Insert( index, value );
   }

   public void Remove( Int16 value )  {
      List.Remove( value );
   }

   public bool Contains( Int16 value )  {
      // If value is not of type Int16, this will return false.
      return( List.Contains( value ) );
   }

   protected override void OnInsert( int index, Object value )  {
      // Insert additional code to be run only when inserting values.
   }

   protected override void OnRemove( int index, Object value )  {
      // Insert additional code to be run only when removing values.
   }

   protected override void OnSet( int index, Object oldValue, Object newValue )  {
      // Insert additional code to be run only when setting values.
   }

   protected override void OnValidate( Object value )  {
      if ( value.GetType() != typeof(System.Int16) )
         throw new ArgumentException( "value must be of type Int16.", "value" );
   }
}

public class SamplesCollectionBase  {

   public static void Main()  {

      // Create and initialize a new CollectionBase.
      Int16Collection myI16 = new Int16Collection();

      // Add elements to the collection.
      myI16.Add( (Int16) 1 );
      myI16.Add( (Int16) 2 );
      myI16.Add( (Int16) 3 );
      myI16.Add( (Int16) 5 );
      myI16.Add( (Int16) 7 );

      // Display the contents of the collection using foreach. This is the preferred method.
      Console.WriteLine( "Contents of the collection (using foreach):" );
      PrintValues1( myI16 );

      // Display the contents of the collection using the enumerator.
      Console.WriteLine( "Contents of the collection (using enumerator):" );
      PrintValues2( myI16 );

      // Display the contents of the collection using the Count property and the Item property.
      Console.WriteLine( "Initial contents of the collection (using Count and Item):" );
      PrintIndexAndValues( myI16 );

      // Search the collection with Contains and IndexOf.
      Console.WriteLine( "Contains 3: {0}", myI16.Contains( 3 ) );
      Console.WriteLine( "2 is at index {0}.", myI16.IndexOf( 2 ) );
      Console.WriteLine();

      // Insert an element into the collection at index 3.
      myI16.Insert( 3, (Int16) 13 );
      Console.WriteLine( "Contents of the collection after inserting at index 3:" );
      PrintIndexAndValues( myI16 );

      // Get and set an element using the index.
      myI16[4] = 123;
      Console.WriteLine( "Contents of the collection after setting the element at index 4 to 123:" );
      PrintIndexAndValues( myI16 );

      // Remove an element from the collection.
      myI16.Remove( (Int16) 2 );

      // Display the contents of the collection using the Count property and the Item property.
      Console.WriteLine( "Contents of the collection after removing the element 2:" );
      PrintIndexAndValues( myI16 );
   }

   // Uses the Count property and the Item property.
   public static void PrintIndexAndValues( Int16Collection 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( Int16Collection myCol )  {
      foreach ( Int16 i16 in myCol )
         Console.WriteLine( "   {0}", i16 );
      Console.WriteLine();
   }

   // Uses the enumerator.
   // NOTE: The foreach statement is the preferred way of enumerating the contents of a collection.
   public static void PrintValues2( Int16Collection 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):
   1
   2
   3
   5
   7

Contents of the collection (using enumerator):
   1
   2
   3
   5
   7

Initial contents of the collection (using Count and Item):
   [0]:   1
   [1]:   2
   [2]:   3
   [3]:   5
   [4]:   7

Contains 3: True
2 is at index 1.

Contents of the collection after inserting at index 3:
   [0]:   1
   [1]:   2
   [2]:   3
   [3]:   13
   [4]:   5
   [5]:   7

Contents of the collection after setting the element at index 4 to 123:
   [0]:   1
   [1]:   2
   [2]:   3
   [3]:   13
   [4]:   123
   [5]:   7

Contents of the collection after removing the element 2:
   [0]:   1
   [1]:   3
   [2]:   13
   [3]:   123
   [4]:   7

*/

Remarks

Important

We don't recommend that you use the CollectionBase class for new development. Instead, we recommend that you use the generic Collection<T> class. For more information, see Non-generic collections shouldn't be used on GitHub.

A CollectionBase instance is always modifiable. See ReadOnlyCollectionBase for a read-only version of this class.

The capacity of a CollectionBase is the number of elements the CollectionBase can hold. As elements are added to a CollectionBase, the capacity is automatically increased as required through reallocation. The capacity can be decreased by setting the Capacity property explicitly.

Notes to Implementers

This base class is provided to make it easier for implementers to create a strongly typed custom collection. Implementers are encouraged to extend this base class instead of creating their own.

Constructors

CollectionBase()

Initializes a new instance of the CollectionBase class with the default initial capacity.

CollectionBase(Int32)

Initializes a new instance of the CollectionBase class with the specified capacity.

Properties

Capacity

Gets or sets the number of elements that the CollectionBase can contain.

Count

Gets the number of elements contained in the CollectionBase instance. This property cannot be overridden.

InnerList

Gets an ArrayList containing the list of elements in the CollectionBase instance.

List

Gets an IList containing the list of elements in the CollectionBase instance.

Methods

Clear()

Removes all objects from the CollectionBase instance. This method cannot be overridden.

Equals(Object)

Determines whether the specified object is equal to the current object.

(Inherited from Object)
GetEnumerator()

Returns an enumerator that iterates through the CollectionBase instance.

GetHashCode()

Serves as the default hash function.

(Inherited from Object)
GetType()

Gets the Type of the current instance.

(Inherited from Object)
MemberwiseClone()

Creates a shallow copy of the current Object.

(Inherited from Object)
OnClear()

Performs additional custom processes when clearing the contents of the CollectionBase instance.

OnClearComplete()

Performs additional custom processes after clearing the contents of the CollectionBase instance.

OnInsert(Int32, Object)

Performs additional custom processes before inserting a new element into the CollectionBase instance.

OnInsertComplete(Int32, Object)

Performs additional custom processes after inserting a new element into the CollectionBase instance.

OnRemove(Int32, Object)

Performs additional custom processes when removing an element from the CollectionBase instance.

OnRemoveComplete(Int32, Object)

Performs additional custom processes after removing an element from the CollectionBase instance.

OnSet(Int32, Object, Object)

Performs additional custom processes before setting a value in the CollectionBase instance.

OnSetComplete(Int32, Object, Object)

Performs additional custom processes after setting a value in the CollectionBase instance.

OnValidate(Object)

Performs additional custom processes when validating a value.

RemoveAt(Int32)

Removes the element at the specified index of the CollectionBase instance. This method is not overridable.

ToString()

Returns a string that represents the current object.

(Inherited from Object)

Explicit Interface Implementations

ICollection.CopyTo(Array, Int32)

Copies the entire CollectionBase to a compatible one-dimensional Array, starting at the specified index of the target array.

ICollection.IsSynchronized

Gets a value indicating whether access to the CollectionBase is synchronized (thread safe).

ICollection.SyncRoot

Gets an object that can be used to synchronize access to the CollectionBase.

IList.Add(Object)

Adds an object to the end of the CollectionBase.

IList.Contains(Object)

Determines whether the CollectionBase contains a specific element.

IList.IndexOf(Object)

Searches for the specified Object and returns the zero-based index of the first occurrence within the entire CollectionBase.

IList.Insert(Int32, Object)

Inserts an element into the CollectionBase at the specified index.

IList.IsFixedSize

Gets a value indicating whether the CollectionBase has a fixed size.

IList.IsReadOnly

Gets a value indicating whether the CollectionBase is read-only.

IList.Item[Int32]

Gets or sets the element at the specified index.

IList.Remove(Object)

Removes the first occurrence of a specific object from the CollectionBase.

Extension Methods

Cast<TResult>(IEnumerable)

Casts the elements of an IEnumerable to the specified type.

OfType<TResult>(IEnumerable)

Filters the elements of an IEnumerable based on a specified type.

AsParallel(IEnumerable)

Enables parallelization of a query.

AsQueryable(IEnumerable)

Converts an IEnumerable to an IQueryable.

Applies to

Product Versions
.NET Core 1.0, Core 1.1, Core 2.0, Core 2.1, Core 2.2, Core 3.0, Core 3.1, 5, 6, 7, 8, 9
.NET Framework 1.1, 2.0, 3.0, 3.5, 4.0, 4.5, 4.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8, 4.8.1
.NET Standard 2.0, 2.1
UWP 10.0

Thread Safety

Public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

This implementation does not provide a synchronized (thread safe) wrapper for a CollectionBase, but derived classes can create their own synchronized versions of the CollectionBase using the SyncRoot property.

Enumerating through a collection is intrinsically not a thread safe procedure. Even when a collection is synchronized, other threads can still modify the collection, which causes the enumerator to throw an exception. 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.

See also