System.Windows.Forms.KeyHelper.GetLastInputChar C# (CSharp) Method

        public static char GetLastInputChar()
        {
            int len = UnityEngine.Input.inputString.Length;
            if (len == 0) return '\0';
            return UnityEngine.Input.inputString[len - 1];
        }

        protected override void OnKeyDown(KeyEventArgs e)
        {
            base.OnKeyDown(e);

            switch (e.KeyCode)
            {
            case Keys.Down:
            case Keys.Right:
                SelectItem(SelectedIndex + 1);
                break;

            case Keys.Left:
            case Keys.Up:
                SelectItem(SelectedIndex - 1);
                break;

            case Keys.PageDown:
                SelectItem(SelectedIndex + visibleItemsCount - 1);
                break;

            case Keys.PageUp:
                SelectItem(SelectedIndex - visibleItemsCount + 1);
                break;

            case Keys.Home:
                SelectItem(0);
                break;

            case Keys.End:
                SelectItem(Items.Count - 1);
                break;

            default:

                // Key filter.
                char c = KeyHelper.GetLastInputChar();
                if (char.IsLetterOrDigit(c) || char.IsPunctuation(c))
                {
                    keyFilter += char.ToLower(c);
                    var itemIndex = FindItemIndex(x => x != null && x.ToString().ToLower().StartsWith(keyFilter));
                    SelectItem(itemIndex);

                    if (keyTimer == null)
                    {
                        keyTimer          = new Timer();
                        keyTimer.Interval = keyFilterResetTime * 1000;
                        keyTimer.Tick    += (sender, args) => ResetKeyFilter();
                    }

                    keyTimer.Stop();
                    keyTimer.Start();
                }
                break;
            }
        }