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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

 
GeneralMuch more simple realization PinPopular
killmeplease15-Apr-11 23:10
killmeplease15-Apr-11 23:10 
GeneralRe: Much more simple realization Pin
dreamgarden29-Sep-13 8:52
dreamgarden29-Sep-13 8:52 
GeneralRe: Much more simple realization Pin
atverweij4-Feb-21 8:04
atverweij4-Feb-21 8:04 
NewsHere is another more general way [modified] Pin
kkyriako@yahoo.com30-Jan-11 8:36
kkyriako@yahoo.com30-Jan-11 8:36 
GeneralRe: Here is another more general way Pin
Muigai Mwaura3-Feb-11 21:22
Muigai Mwaura3-Feb-11 21:22 
QuestionRe: Here is another more general way Pin
Michael Ehrt20-Feb-11 20:11
Michael Ehrt20-Feb-11 20:11 
GeneralRe: Here is another more general way Pin
Gianni Gardini 21-Feb-11 0:30
Gianni Gardini 21-Feb-11 0:30 
GeneralRe: Here is another more general way Pin
CloudAtlas228-Nov-11 22:57
CloudAtlas228-Nov-11 22:57 
I bugfixed the code because because the SortingProperty and SortDirection weren't updated. Also, when one of the to be sorted columns contained a NULL value the thing crashed. Here's the result:

C#
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.ComponentModel;
using System.Linq.Expressions;

namespace Tools.Utilities
{
    public class SortableBindingList<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<SortableBindingList<T>, List<T>> populateBaseList = (a, b) => a.ResetItems(b);

        class PropertyCompare : IComparer<T>
        {
            PropertyDescriptor _property;           // The propery value
            ListSortDirection _direction;           // The direction of compare

            public PropertyCompare(PropertyDescriptor property, ListSortDirection direction)
            {
                _property = property;
                _direction = direction;
            }

            public int Compare(T comp1, T comp2)
            {
                var value1 = _property.GetValue(comp1) as IComparable;
                var value2 = _property.GetValue(comp2) as IComparable;

                if (value1 == value2)
                {
                    return 0;
                }

                if (_direction == ListSortDirection.Ascending)
                {
                    if (value1 != null)
                    {
                        return value1.CompareTo(value2);
                    }
                    else
                    {
                        return -1;
                    }
                }
                else
                {
                    if (value2 != null)
                    {
                        return value2.CompareTo(value1);
                    }
                    else
                    {
                        return 1;
                    }
                }
            }
        }

        public SortableBindingList()
        {
            _originalList = new List<T>();
        }

        public SortableBindingList(IEnumerable<T> enumerable)
        {
            _originalList = new List<T>(enumerable);
            populateBaseList(this, _originalList);
        }

        public SortableBindingList(List<T> list)
        {
            _originalList = list;
            populateBaseList(this, _originalList);
        }

        protected override void ApplySortCore(PropertyDescriptor prop, ListSortDirection direction)
        {
            _sortProperty = prop;
            _sortDirection = direction;

            PropertyCompare comp = new PropertyCompare(prop, _sortDirection);
            List<T> sortedList = new List<T>(this);
            sortedList.Sort(comp);
            ResetItems(sortedList);

            ResetBindings();

            // toggle sort
            _sortDirection = (_sortDirection == ListSortDirection.Ascending) ? ListSortDirection.Descending : ListSortDirection.Ascending;
        }


        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();
        }
    }
}


I hope it's useful to somebody.

modified 29-Nov-11 5:05am.

GeneralRe: Here is another more general way Pin
Sonam K27-Dec-12 22:58
Sonam K27-Dec-12 22:58 
GeneralMy vote of 5 Pin
_clem25-Jan-11 6:36
_clem25-Jan-11 6:36 
GeneralRe: My vote of 5 Pin
Muigai Mwaura27-Jan-11 6:37
Muigai Mwaura27-Jan-11 6:37 
GeneralNot perfect Pin
Member 740954117-Nov-10 0:51
Member 740954117-Nov-10 0:51 
GeneralRe: Not perfect Pin
Muigai Mwaura27-Jan-11 6:38
Muigai Mwaura27-Jan-11 6:38 
Generalmy vote of 5 Pin
unami8224-Sep-10 5:09
unami8224-Sep-10 5:09 
GeneralRe: my vote of 5 Pin
Muigai Mwaura24-Sep-10 6:38
Muigai Mwaura24-Sep-10 6:38 
NewsCodeplex Pin
Muigai Mwaura8-Aug-10 20:32
Muigai Mwaura8-Aug-10 20:32 
QuestionIs this a bug? Pin
Jason Brown26-Jul-10 6:28
Jason Brown26-Jul-10 6:28 
AnswerRe: Is this a bug? Pin
Muigai Mwaura27-Jul-10 1:23
Muigai Mwaura27-Jul-10 1:23 
GeneralRe: Is this a bug? Pin
Daniel Castenholz5-Aug-10 7:35
Daniel Castenholz5-Aug-10 7:35 
GeneralRe: Is this a bug? Pin
Muigai Mwaura5-Aug-10 22:12
Muigai Mwaura5-Aug-10 22:12 
GeneralMy vote of 5 Pin
Jason Brown26-Jul-10 0:46
Jason Brown26-Jul-10 0:46 
GeneralRe: My vote of 5 Pin
Muigai Mwaura27-Jul-10 1:21
Muigai Mwaura27-Jul-10 1:21 
GeneralMy vote of 5 Pin
Member 15999454-Jul-10 3:35
Member 15999454-Jul-10 3:35 
GeneralRe: My vote of 5 Pin
Muigai Mwaura20-Jul-10 0:02
Muigai Mwaura20-Jul-10 0:02 
GeneralPlease Fix yours amazing class Pin
minskowl25-Sep-09 3:47
minskowl25-Sep-09 3:47 

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