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SmartLists - Extended Lists with Events

, 29 Sep 2010
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SmartLists library is a collection of classes that extends the standard C# List object

Introduction

SmartLists library is a collection of classes that extends the standard C# List<T> object. Better: they implement the IList<T> interface, wrapping the List<T> object and adding more functionalities to it.

These lists implements solutions to common issues that usually happen when dealing with Lists. As an example, a list with a "Parent" object that is consistently updated between the elements of the list and the list itself.

These lists are not designed for performance but with easy of use and consistency in mind. If you look for performance, you better look into other kind of lists that are designed for that.

EventList

This is a list that generates events when elements are added, inserted, removed, swapped and when it is cleared. Events are generated before and after these actions, so that we can cancel the action or take further actions after the action.

Some examples of use of the events could be:

  1. To check an object before it's added to the list so that objects with inconsistent properties are not added to the list
  2. To avoid that some kind of elements are removed from the list
  3. To update GUI elements after some actions are taken on a list

NamedList

This is an EventList that requires its elements to have a Name (string) property (INamed interface). In this kind of list, you can't add elements with the same name. The name comparison can be set to be case sensitive or not.

/// <summary>
/// Object that have a Name (property)
/// </summary>
public interface INamed
{
    /// <summary>
    /// Event fired before the Name of the object is changed
    /// Operation can be cancelled
    /// </summary>
    event CancelRenameEventHandler BeforeNameChanged;
    /// <summary>
    /// Event fired when the object has changed it's Name
    /// </summary>
    event EventHandler NameChanged;
    /// <summary>
    /// Name of the object
    /// </summary>
    string Name { get; }
}

ParentedList

This is an EventList where its elements and the list itself have a Parent object (IParented<T> interface). And we want this Parent property to be updated automatically when the object is added or removed from the list or the list's parent changes. This is really quite a common situation that happens really often and is usually coded in the most wrong and inconsistent ways.

/// <summary>
/// Objects implementing this interface have a parent object
/// </summary>
/// <typeparam name="T">Type of the parent object</typeparam>
public interface IParented<T>
{
    /// <summary>
    /// Event generated when the Parent property is changed
    /// </summary>
    event EventHandler ParentChanged;
    /// <summary>
    /// Get or set the Parent object
    /// </summary>
    T Parent
    {
        get;
        set;
    }
}

ParentedNamedList

This is an EventList that puts together the features of the NamedList and the ParentedList. So in this kind of list, we will have items with a Name and a Parent property.

An example of use of this kind of list is a list of a database table fields. The fields have of course a Name and a Parent (the table). When a field is removed or created and added to the list, its parent is updated automatically by the list. Of course, you can't add two fields with the same name: and of course you can't rename a field with the name of another field (this generates a DuplicatedNameException). This is all handled automatically by the ParentedNamedList. The only thing the developer needs to do is create a Field object that implements the INamed and the IParent<T> interfaces.

License

This article, along with any associated source code and files, is licensed under The BSD License

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About the Author

Luigi Grilli
Software Developer (Senior) Scee
United Kingdom United Kingdom
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Comments and Discussions

 
GeneralMost of this exists in the BCL PinmemberWilliam E. Kempf30-Sep-10 3:15 
GeneralRe: Most of this exists in the BCL PinmemberLuigi Grilli30-Sep-10 3:40 
GeneralMy vote of 4 PinmemberMichela Carriero - Lyra29-Sep-10 21:18 

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