CA1010: Collections should implement generic interface

TypeName	CollectionsShouldImplementGenericInterface
CheckId	CA1010
Category	Microsoft.Design
Breaking Change	Non-breaking

Cause

An externally visible type implements the IEnumerable interface but does not implement the IEnumerable interface, and the containing assembly targets .NET Framework 2.0. This rule ignores types that implement IDictionary.

Rule Description

To broaden the usability of a collection, implement one of the generic collection interfaces. Then the collection can be used to populate generic collection types such as the following:

• List

• Queue

• Stack

How to Fix Violations

To fix a violation of this rule, implement one of the following generic collection interfaces:

• IEnumerable

• ICollection

• IList

When to Suppress Warnings

It is safe to suppress a warning from this rule; however, the collection will have a more limited use.

Example Violation

Description

The following example shows a class (reference type) that derives from the non-generic CollectionBase class, which violates this rule.

Code

using System;
using System.Collections;

namespace Samples
{
    public class Book
    {
        public Book()
        {
        }
    }

    public class BookCollection : CollectionBase
    {
        public BookCollection()
        {
        }

        public void Add(Book value)
        {
            InnerList.Add(value);
        }

        public void Remove(Book value)
        {
            InnerList.Remove(value);
        }

        public void Insert(int index, Book value)
        {
            InnerList.Insert(index, value);
        }

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

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

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

        public void CopyTo(Book[] array, int arrayIndex)
        {
            InnerList.CopyTo(array, arrayIndex);
        }
    }
}

Comments

To fix a violation of this violation, you should either implement the generic interfaces or change the base class to a type that already implements both the generic and non-generic interfaces, such as the Collection<T> class.

Fix by Base Class Change

Description

The following example fixes the violation by changing the base class of the collection from the non-generic CollectionBase class to the generic Collection<T> (Collection(Of T) in Visual Basic) class.

Code

using System;
using System.Collections.ObjectModel; 

namespace Samples
{    
    public class Book        
    {               
        public Book()                
        {                
        }        
    }    

    public class BookCollection : Collection<Book>    
    {        
        public BookCollection()        
        {        
        }    
    }
}

Comments

Changing the base class of an already released class is considered a breaking change to existing consumers.

Fix by Interface Implementation

Description

The following example fixes the violation by implementing these generic interfaces: IEnumerable<T>, ICollection<T>, and IList<T> (IEnumerable(Of T), ICollection(Of T), and IList(Of T) in Visual Basic).

Code

using System;
using System.Collections;
using System.Collections.Generic;

namespace Samples
{
    public class Book
    {
        public Book()
        {
        }
    }

    public class BookCollection : CollectionBase, IList<Book>
    {
        public BookCollection()
        {
        }

        int IList<Book>.IndexOf(Book item)
        {
            return this.List.IndexOf(item);
        }

        void IList<Book>.Insert(int location, Book item)
        {
        }

        Book IList<Book>.this[int index]
        {
            get { return (Book) this.List[index]; }
            set { }
        }

        void ICollection<Book>.Add(Book item)
        {
        }

        bool ICollection<Book>.Contains(Book item)
        {
            return true;
        }

        void ICollection<Book>.CopyTo(Book[] array, int arrayIndex)
        {
        }

        bool ICollection<Book>.IsReadOnly
        {
            get { return false; }
        }

        bool ICollection<Book>.Remove(Book item)
        {
            if (InnerList.Contains(item))
            {
                InnerList.Remove(item);
                return true;
            }
            return false;
        }

        IEnumerator<Book> IEnumerable<Book>.GetEnumerator()
        {
            return new BookCollectionEnumerator(InnerList.GetEnumerator());
        }

        private class BookCollectionEnumerator : IEnumerator<Book>
        {
            private IEnumerator _Enumerator;

            public BookCollectionEnumerator(IEnumerator enumerator)
            {
                _Enumerator = enumerator;
            }

            public Book Current
            {
                get { return (Book)_Enumerator.Current; }
            }

            object IEnumerator.Current
            {
                get { return _Enumerator.Current; }
            }

            public bool MoveNext()
            {
                return _Enumerator.MoveNext();
            }

            public void Reset()
            {
                _Enumerator.Reset();
            }

            public void Dispose()
            {
            }
        }
    }
}

Related Rules

CA1005: Avoid excessive parameters on generic types

CA1000: Do not declare static members on generic types

CA1002: Do not expose generic lists

CA1006: Do not nest generic types in member signatures

CA1004: Generic methods should provide type parameter

CA1003: Use generic event handler instances

CA1007: Use generics where appropriate

See Also

Reference

Generics (C# Programming Guide)