Strongly typed collection without generics

Question

Good Morning Sir/Madam Let us say that I created a class… public class Subject { private string _code; private string _description; public string Code { get { return _code; } set { _code = value ; } } public string Description { get { return _description; } set { _description = value ; } } // end property public Subject() { //empty default } // end method public Subject( string Code string Description) { this .Code = Code; this .Description = Description; } // end method public override string ToString() { return _code +  :  + _description; } // end method } Then I want to create a strongly typed collection used to store Subject objects but then I don't want to store duplicate objects with the : public void Add(Subject subjectObj) Please help me out.. Normal 0 false false false EN-ZA X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:Table Normal; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin-top:0cm; mso-para-margin-right:0cm; mso-para-margin-bottom:10.0pt; mso-para-margin-left:0cm; line-height:115%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:Calibrisans-serif; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-fareast-language:EN-US;}

Vulpes · Answer

If you want to implement a strongly typed collection without using generics then the best approach is to implement CollectionBase which does most of the work for you: http://msdn.microsoft.com/en-us/library/7a03ybbb(v=vs.100).aspx So in this case I'd use: using System; using System.Collections; public class Subject { private string _code; private string _description; public string Code { get { return _code; } set { _code = value; } } public string Description { get { return _description; } set { _description = value; } } // end property public Subject() { //empty default } // end method public Subject(string Code string Description) { this.Code = Code; this.Description = Description; } // end method public override string ToString() { return _code +  :  + _description; } // end method } public class SubjectCollection : CollectionBase { public Subject this[int index] { get { return (Subject) List[index]; } set { List[index] = value; } } public int Add(Subject value) { return List.Add(value); } public int IndexOf(Subject value) { return List.IndexOf(value); } public void Insert(int index Subject value) { List.Insert(index value); } public void Remove(Subject value) { List.Remove(value); } public bool Contains(Subject value) { // If value is not of type Subject this will return false. return List.Contains(value); } protected override void OnInsert(int index Object value) { if (List.Contains((Subject)value)) throw new ArgumentException(Can't add or insert duplicate objects. value); } protected override void OnSet(int index Object oldValue Object newValue) { if (!Object.Equals(oldValue newValue) && List.Contains((Subject)newValue)) throw new ArgumentException(Can't set elements to duplicate objects. value); } protected override void OnValidate(Object value ) { if (value.GetType() != typeof(Subject)) throw new ArgumentException(value must be of type Subject. value); } } class Test { static void Main() { SubjectCollection sc = new SubjectCollection(); Subject s1 = new Subject(M1 Maths); Subject s2 = new Subject(P1 Physics); sc.Add(s1); sc.Add(s2); foreach(Subject s in sc) { Console.WriteLine(Code = {0} Subject = {1} s.Code s.Description); } sc[0] = s1; // OK setting to same object //sc.Add(s1); //sc[1] = s1; Console.ReadKey(); } } If you try to uncomment either of the lines in bold then you will get a 'duplicate object' exception. Incidentally when you say duplicate object I've taken it that you mean the same object and not just a different object which happens to have the same Code and Description properties.