List and Collection in c#

Question

Hello friend Here is List and Collection of questions: 1)List and Collection of difference? 2)Under what circumstances we need to rewrite InsertItem and ClearItems methods? Can you give some examples of it? 3) Their respective advantages in terms of performance? Thank in advance.

Vulpes · Answer

Basically the Collection class provides us with a customizable wrapper for a generic indexable collection such as List . It allows us to implement customized behavior when items are added to inserted in or removed from the collection. You can also control what happens when items are replaced by other items or the entire collection is cleared. Although you could do this by writing your own class or deriving directly from List  it saves a lot of work if you derive from Collection instead. This is because Collection provides the following protected virtual methods over and above what List provides: InsertItem RemoveItem ClearItems SetItem When the Add Insert Remove RemoveAt Clear methods or the Indexer setter are invoked these methods are called internally to do the actual work. However as they are virtual you can override them to provide your own customized behavior. You'd normally call the base class method before or after adding your own code depending on the circumstances. There's a good example of using Collection in its MSDN documentation (example 2): https://msdn.microsoft.com/en-us/library/ms132397%28v=vs.110%29.aspx Here a collection of dinosaurs is being created. However it is desired to add an event which fires whenever there's a change to the collection so a simple List will not suffice. You therefore need to create a Dinsoaurs class which derives from Collection so you can override each of the above methods to fire an event when a change occurs. Unless you override these methods Collection will behave much the same as List as example 1 in the above MSDN link shows. So if you don't want to customize its behavior then it's better to use List directly rather than Collection as the former should be slightly faster and smaller without the wrapper code including the hooks to the protected methods.

Ken H · Answer

Thank for you. :)

Francis · Answer

Please find the answer below for your questions: 1. List - Denotes the concept called Generics. You can find difference between collection and genereics here . 2. ASFAIK there is no such circumstances most of the time you can reuse the existing. Also there is NO InsertItem and ClearItems method. 3. The above URL itself contains answer for this question.

List<T> and Collection in c#