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Implementing a Sortable BindingList Very, Very Quickly

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1 Dec 2008CPOL2 min read 278.6K   4.6K   87   67
A custom implementation of BindingList that provides sorting for every property of type T.

SortableBindingList

Introduction

Implementing parent-child hierarchies (for example, a Sale object and the SaleDetails associated with it) is one of the most common scenarios encountered when modeling the entities in a business domain. If you implement the business objects using classes, a collection of child objects will typically be stored in a List<T>. However, List<T>, will prove anemic should you require a rich user interface built on top of the .NET framework's support for data binding.

The typical solution will be to wrap the List<T> in a BindingSource in order to take advantage of its design time support for data binding. That road will only take you so far as a critical feature will be absent - support for sorting.

This article will seek to remedy that by providing a custom implementation of a BindingList<T> that will automatically provide the methods required to provide sorting capability on every property defined in type T.

Implementation Objectives

  • Support sorting on all properties by instantiating an instance of the custom implementation of the BindingList<T>. E.g., write:
  • C#
    MySortableBindingList<SaleDetails>sortableSaleDetails = 
                          new MySortableBindingList<SaleDetail>();

    and get the sorting functionality.

Motivating Example

To illustrate this approach, we shall model two classes, Sale and SaleDetail, as follows:

C#
public class Sale {

    public Sale() {
        SaleDate = DateTime.Now;
    }

    public MySortableBindingList<SaleDetail> SaleDetails { get; set; }
    public string Salesman { get; set; }
    public string Client { get; set; }
    public DateTime SaleDate { get; set; }

    public decimal TotalAmount {
        get {
            Debug.Assert(SaleDetails != null);
            return SaleDetails.Sum(a => a.TotalAmount);
        }
    }
}

public class SaleDetail {

    public string Product { get; set; }
    public int Quantity { get; set; }
    public decimal UnitPrice { get; set; }

    public decimal TotalAmount {
        get {
            return UnitPrice * Quantity;
        }
    }
}

The above classes are just simple enough to illustrate the main concepts behind the article, as validation, persistence, error handling etc., are beyond the scope of the article.

Subclassing BindingList<T>

First, the code:

C#
public class MySortableBindingList<T> : BindingList<T> {

    // reference to the list provided at the time of instantiation
    List<T> originalList;
    ListSortDirection sortDirection;
    PropertyDescriptor sortProperty;

    // function that refereshes the contents
    // of the base classes collection of elements
    Action<MySortableBindingList<T>, List<T>> 
                   populateBaseList = (a, b) => a.ResetItems(b);

    // a cache of functions that perform the sorting
    // for a given type, property, and sort direction
    static Dictionary<string, Func<List<T>, IEnumerable<T>>> 
       cachedOrderByExpressions = new Dictionary<string, Func<List<T>, 
                                                 IEnumerable<T>>>();

    public MySortableBindingList() {
        originalList = new List<T>();
    }

    public MySortableBindingList(IEnumerable<T> enumerable) {
        originalList = enumerable.ToList();
        populateBaseList(this, originalList);
    }

    public MySortableBindingList(List<T> list) {
        originalList = list;
        populateBaseList(this, originalList);
    }

    protected override void ApplySortCore(PropertyDescriptor prop, 
                            ListSortDirection direction) {
        /*
         Look for an appropriate sort method in the cache if not found .
         Call CreateOrderByMethod to create one. 
         Apply it to the original list.
         Notify any bound controls that the sort has been applied.
         */

        sortProperty = prop;

        var orderByMethodName = sortDirection == 
            ListSortDirection.Ascending ? "OrderBy" : "OrderByDescending";
        var cacheKey = typeof(T).GUID + prop.Name + orderByMethodName;

        if (!cachedOrderByExpressions.ContainsKey(cacheKey)) {
            CreateOrderByMethod(prop, orderByMethodName, cacheKey);
        }

        ResetItems(cachedOrderByExpressions[cacheKey](originalList).ToList());
        ResetBindings();
        sortDirection = sortDirection == ListSortDirection.Ascending ? 
                        ListSortDirection.Descending : ListSortDirection.Ascending;
    }


    private void CreateOrderByMethod(PropertyDescriptor prop, 
                 string orderByMethodName, string cacheKey) {

        /*
         Create a generic method implementation for IEnumerable<T>.
         Cache it.
        */

        var sourceParameter = Expression.Parameter(typeof(List<T>), "source");
        var lambdaParameter = Expression.Parameter(typeof(T), "lambdaParameter");
        var accesedMember = typeof(T).GetProperty(prop.Name);
        var propertySelectorLambda =
            Expression.Lambda(Expression.MakeMemberAccess(lambdaParameter, 
                              accesedMember), lambdaParameter);
        var orderByMethod = typeof(Enumerable).GetMethods()
                                      .Where(a => a.Name == orderByMethodName &&
                                                   a.GetParameters().Length == 2)
                                      .Single()
                                      .MakeGenericMethod(typeof(T), prop.PropertyType);

        var orderByExpression = Expression.Lambda<Func<List<T>, IEnumerable<T>>>(
                                    Expression.Call(orderByMethod,
                                            new Expression[] { sourceParameter, 
                                                               propertySelectorLambda }),
                                            sourceParameter);

        cachedOrderByExpressions.Add(cacheKey, orderByExpression.Compile());
    }

    protected override void RemoveSortCore() {
        ResetItems(originalList);
    }

    private void ResetItems(List<T> items) {

        base.ClearItems();

        for (int i = 0; i < items.Count; i++) {
            base.InsertItem(i, items[i]);
        }
    }

    protected override bool SupportsSortingCore {
        get {
            // indeed we do
            return true;
        }
    }

    protected override ListSortDirection SortDirectionCore {
        get {
            return sortDirection;
        }
    }

    protected override PropertyDescriptor SortPropertyCore {
        get {
            return sortProperty;
        }
    }

    protected override void OnListChanged(ListChangedEventArgs e) {
        originalList = base.Items.ToList();
    }
}

In a Nutshell

If, for instance, you create a MySortableBindingList<Sale> and sort on the Customer property, an expression that conceptually looks something like Enumerable.OrderBy<Sale>(originalList, a => a.Customer) will be created and used to do the sorting.

The code to create the sample data and set up the data binding:

C#
public void OnLoad(object source, EventArgs e) {

    var sales = new[] {
        new Sale(){

            Client = "Jahmani Mwaura",
            SaleDate = new DateTime(2008,1,1),
            Salesman = "Gachie",

            SaleDetails = new MySortableBindingList<SaleDetail>(){

                new SaleDetail(){
                    Product = "Sportsman",
                    Quantity = 1,
                    UnitPrice = 80
                },

                 new SaleDetail(){
                    Product = "Tusker Malt",
                    Quantity = 2,
                    UnitPrice = 100
                },

                new SaleDetail(){
                    Product = "Alvaro",
                    Quantity = 1,
                    UnitPrice = 50
                }
            }
        },

        new Sale(){

            Client = "Ben Kones",
            SaleDate = new DateTime(2008,1,1),
            Salesman = "Danny",

            SaleDetails = new MySortableBindingList<SaleDetail>(){

                new SaleDetail(){
                    Product = "Embassy Kings",
                    Quantity = 1,
                    UnitPrice = 80
                },

                 new SaleDetail(){
                    Product = "Tusker",
                    Quantity = 5,
                    UnitPrice = 100
                },

                new SaleDetail(){
                    Product = "Novida",
                    Quantity = 3,
                    UnitPrice = 50
                }
            }
        },

        new Sale(){

            Client = "Tim Kim",
            SaleDate = new DateTime(2008,1,1),
            Salesman = "Kiplagat",

            SaleDetails = new MySortableBindingList<SaleDetail>(){

                new SaleDetail(){
                    Product = "Citizen Special",
                    Quantity = 10,
                    UnitPrice = 30

                },

                new SaleDetail(){
                    Product = "Burn",
                    Quantity = 2,
                    UnitPrice = 100
                }
            }
        }
    };

    saleBindingSource.DataSource = new MySortableBindingList<Sale>(sales);
}

Seeing it at work

You can download the samples at the top of the page and see it at work for yourself. I hope you enjoy.

Cheers!

History

  • December 2, 2008: Article posted.

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


Written By
Technical Lead Olivine Technology
Kenya Kenya
Technical Lead, Olivine Technology - Nairobi, Kenya.

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Comments and Discussions

 
GeneralSeems to break automatic list change notifications... Pin
Sly2aar27-Jan-09 0:15
Sly2aar27-Jan-09 0:15 
GeneralRe: Seems to break automatic list change notifications... Pin
Sly2aar27-Jan-09 0:55
Sly2aar27-Jan-09 0:55 
GeneralRe: Seems to break automatic list change notifications... [modified] Pin
Muigai Mwaura28-Jan-09 22:19
Muigai Mwaura28-Jan-09 22:19 
GeneralRe: Seems to break automatic list change notifications... Pin
Sly2aar29-Jan-09 1:32
Sly2aar29-Jan-09 1:32 
GeneralRe: Seems to break automatic list change notifications... Pin
Drew Loika2-Feb-09 17:08
Drew Loika2-Feb-09 17:08 
GeneralRe: Seems to break automatic list change notifications... Pin
Muigai Mwaura2-Feb-09 20:42
Muigai Mwaura2-Feb-09 20:42 

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