netch/NetchLib/SearchComboBox.cs

using System.Linq;

namespace System.Windows.Forms
{
    [System.ComponentModel.DesignerCategory(@"Code")]
    public class SearchComboBox : ComboBox
    {
        public SearchComboBox()
        {
            AutoCompleteMode = AutoCompleteMode.Suggest;
        }

        protected override void OnTextChanged(EventArgs e)
        {
            try
            {
                if (DesignMode || !string.IsNullOrEmpty(Text) || !Visible) return;

                ResetCompletionList();
            }
            finally
            {
                base.OnTextChanged(e);
            }
        }

        protected override void OnKeyUp(KeyEventArgs e)
        {
            try
            {
                if (DesignMode || e.KeyData == Keys.Up || e.KeyData == Keys.Down) return;

                if (e.KeyData == Keys.Return)
                {
                    e.Handled = true;
                    if (newList.Length > 0 && !newList.Select(o => o.ToString()).Contains(Text))
                    {
                        Text = newList[0].ToString();
                    }

                    DroppedDown = false;
                    return;
                }

                ReevaluateCompletionList();
            }
            finally
            {
                base.OnKeyUp(e);
            }
        }

        private void ResetCompletionList()
        {
            _previousSearchTerm = null;
            try
            {
                SuspendLayout();

                var originalList = (object[])Tag;
                if (originalList == null)
                {
                    Tag = originalList = Items.Cast<object>().ToArray();
                }

                if (Items.Count == originalList.Length) return;

                while (Items.Count > 0)
                {
                    Items.RemoveAt(0);
                }

                Items.AddRange(originalList);
            }
            finally
            {
                ResumeLayout(true);
            }
        }

        private string _previousSearchTerm;
        private object[] newList;
        private void ReevaluateCompletionList()
        {
            try
            {
                var currentSearchTerm = Text.ToLowerInvariant();
                if (currentSearchTerm == _previousSearchTerm) return;

                _previousSearchTerm = currentSearchTerm;
                try
                {
                    SuspendLayout();

                    var originalList = (object[])Tag;
                    if (originalList == null)
                    {
                        Tag = originalList = Items.Cast<object>().ToArray();
                    }

                    if (string.IsNullOrEmpty(currentSearchTerm))
                    {
                        if (Items.Count == originalList.Length) return;

                        newList = originalList;
                    }
                    else
                    {
                        newList = originalList.Where(x => x.ToString().ToLowerInvariant().Contains(currentSearchTerm)).ToArray();
                    }

                    try
                    {
                        while (Items.Count > 0)
                        {
                            Items.RemoveAt(0);
                        }
                    }
                    catch
                    {
                        try
                        {
                            Items.Clear();
                        }
                        catch
                        {
                            // ignored
                        }
                    }

                    Items.AddRange(newList.ToArray());
                }
                finally
                {
                    if (currentSearchTerm.Length >= 2 && !DroppedDown)
                    {
                        DroppedDown = true;
                        Cursor.Current = Cursors.Default;
                        Text = currentSearchTerm;
                        Select(currentSearchTerm.Length, 0);
                    }

                    if (Items.Count > 0)
                    {
                        DroppedDown = false;
                        DroppedDown = true;
                    }

                    ResumeLayout(true);
                }
            }
            catch
            {
                // ignored
            }
        }
    }
}