CA1010: Collections should implement generic interface

Cause

An externally visible type implements the System.Collections.IEnumerable interface but does not implement the System.Collections.Generic.IEnumerable<T> interface, and the containing assembly targets .NET Framework 2.0. This rule ignores types that implement System.Collections.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:

• System.Collections.Generic.List<T>

• System.Collections.Generic.Queue<T>

• System.Collections.Generic.Stack<T>

How to Fix Violations

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

• System.Collections.Generic.IEnumerable<T>

• System.Collections.Generic.ICollection<T>

• System.Collections.Generic.IList<T>

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

Generics