c# - Using SortableBindingList<T> - DataGridView doesn't automatically sort on changes

Question

I'm building a Windows Forms Application that displays a custom class Record objects and sorts them by how long they've been in my SortableBindingList<Record> record_list. When I start my program, I have some "dummy" records loaded into this list already for the sake of testing.

The SortableBindingList<T> has been taken from here.

public partial class Form1 : Form
{
    public SortableBindingList<Record> record_list = new SortableBindingList<Record> { };
    public static DataGridViewCellStyle style = new DataGridViewCellStyle();
    public Form1()
    {
        InitializeComponent();
        dataGridView.DataSource = record_list;
        FillData(); //Temporary function to insert dummy data for demo.
        dataGridView.CellFormatting += new System.Windows.Forms.DataGridViewCellFormattingEventHandler(this.cell_formatting);
        this.Controls.Add(dataGridView);
        this.dataGridView.RowHeadersVisible = false;
        this.dataGridView.Sort(this.dataGridView.Columns["UserName"], ListSortDirection.Ascending);

        start_timer();                 
    }

Result before "new" data is added (note: this was alphabetized automatically, specifically entered into the list out of alphabetical order):

Result after data is added:

Finally, result after I click the "UserName" header:

So, must I force a sort every time my DataSource is updated? If that's the case, how do I call a sort in such a manner?

Thank you for your assistance in advance!

Answer 1

You need to apply sort when the list changes.

The SortableBindingList<T> needs some changes to keep the the list sorted when some changes made in list. Here is the full code with changes which I made.

Pay attention The OnListChanged method of BindingList will be called automatically after adding and removing items. But if you need to OnListChanged also runs after changing properties of items, you should implement INotifyPropertyChanged for your model class.

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
public class SortableBindingList<T> : BindingList<T>
{
    private bool isSortedValue;
    ListSortDirection sortDirectionValue;
    PropertyDescriptor sortPropertyValue;
    public SortableBindingList() : base() { }
    public SortableBindingList(IList<T> list) : base(list) { }
    protected override void ApplySortCore(PropertyDescriptor prop,
        ListSortDirection direction)
    {
        Type interfaceType = prop.PropertyType.GetInterface("IComparable");
        if (interfaceType == null && prop.PropertyType.IsValueType)
        {
            Type underlyingType = Nullable.GetUnderlyingType(prop.PropertyType);
            if (underlyingType != null)
            {
                interfaceType = underlyingType.GetInterface("IComparable");
            }
        }
        if (interfaceType != null)
        {
            sortPropertyValue = prop;
            sortDirectionValue = direction;
            IEnumerable<T> query = base.Items;
            if (direction == ListSortDirection.Ascending)
                query = query.OrderBy(i => prop.GetValue(i));
            else
                query = query.OrderByDescending(i => prop.GetValue(i));
            int newIndex = 0;
            foreach (object item in query)
            {
                this.Items[newIndex] = (T)item;
                newIndex++;
            }
            isSortedValue = true;
            sorting = true;
            this.OnListChanged(new ListChangedEventArgs(ListChangedType.Reset, -1));
            sorting = false;
        }
        else
        {
            throw new NotSupportedException("Cannot sort by " + prop.Name +
                ". This" + prop.PropertyType.ToString() +
                " does not implement IComparable");
        }
    }
    bool sorting = false;
    protected override PropertyDescriptor SortPropertyCore
    {
        get { return sortPropertyValue; }
    }
    protected override ListSortDirection SortDirectionCore
    {
        get { return sortDirectionValue; }
    }
    protected override bool SupportsSortingCore
    {
        get { return true; }
    }
    protected override bool IsSortedCore
    {
        get { return isSortedValue; }
    }
    protected override void RemoveSortCore()
    {
        isSortedValue = false;
        sortPropertyValue = null;
    }
    protected override void OnListChanged(ListChangedEventArgs e)
    {
        if (!sorting && sortPropertyValue != null)
            ApplySortCore(sortPropertyValue, sortDirectionValue);
        else
            base.OnListChanged(e);
    }
}