Hotkey input box for WinForms

HotkeyInputBox.cs

// HotkeyInputBox 0.1 (c) 2011 Richard Z.H. Wang
// MIT licensed.

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Runtime.InteropServices;

namespace Uploadinator.Controls
{
    class HotkeyInputBox : TextBox
    {
        public HotkeyInputBox() { }

        #region Properties to hide from the designer
        [Browsable(false)]
        public new string[] Lines { get { return new string[] { Text }; } private set { base.Lines = value; } }
        [Browsable(false)]
        public override bool Multiline { get { return false; } }
        [Browsable(false)]
        public new char PasswordChar { get; set; }
        [Browsable(false)]
        public new ScrollBars ScrollBars { get; set; }
        [Browsable(false)]
        public override bool ShortcutsEnabled { get { return false; } }
        [Browsable(false)]
        public override string Text { get { return base.Text; } set { base.Text = value; } }
        [Browsable(false)]
        public new bool WordWrap { get; set; }
        #endregion

        #region Focus detection - use this to stop hotkeys being triggered in your code
        private static Control FindFocusedControl(Control control)
        {
            var container = control as ContainerControl;
            while (container != null)
            {
                control = container.ActiveControl;
                container = control as ContainerControl;
            }
            return control;
        }
        public bool IsFocused { get { return FindFocusedControl(Form.ActiveForm) == this; } }
        public static bool TypeIsFocused { get { return FindFocusedControl(Form.ActiveForm) is HotkeyInputBox; } }
        #endregion

        private Hotkey _hotkey = new Hotkey();

        public Keys KeyCode { get { return _hotkey.KeyCode; } set { _hotkey.KeyCode = value; } }
        public bool Windows { get { return _hotkey.Windows; } set { _hotkey.Windows = value; } }
        public bool Control { get { return _hotkey.Control; } set { _hotkey.Control = value; } }
        public bool Alt { get { return _hotkey.Alt; } set { _hotkey.Alt = value; } }
        public bool Shift { get { return _hotkey.Shift; } set { _hotkey.Shift = value; } }

        public void SetHotkey(Hotkey hotkey)
        {
            _hotkey = hotkey;
        }
        public void SetHotkey(string jsonSerializedHotkey)
        {
            var s = new System.Web.Script.Serialization.JavaScriptSerializer();
            _hotkey = s.Deserialize<Hotkey>(jsonSerializedHotkey);
        }
        public Hotkey GetHotkey()
        {
            return _hotkey.Clone();
        }
        public string GetJsonHotkey()
        {
            var s = new System.Web.Script.Serialization.JavaScriptSerializer();
            return s.Serialize(_hotkey);
        }

        public void Reset()
        {
            KeyCode = Keys.None;
            Windows = false;
            Control = false;
            Alt = false;
            Shift = false;
        }

        private void RefreshText()
        {
            Text = _hotkey.ToString(true);
            Invalidate();
        }

        protected override void OnPaint(PaintEventArgs e)
        {
            RefreshText();
            base.OnPaint(e);
        }

        protected override void OnMouseMove(MouseEventArgs e)
        {
            if (e.Button != System.Windows.Forms.MouseButtons.None)
                SelectAll();
            base.OnMouseMove(e);
        }

        public event EventHandler HotkeyChanged;
        protected virtual void OnHotkeyChanged(EventArgs e)
        {
            if (HotkeyChanged != null)
                HotkeyChanged(this, e);
        }

        const int WM_KEYDOWN = 0x100;
        const int WM_KEYUP = 0x101;
        const int WM_CHAR = 0x102;
        const int WM_SYSCHAR = 0x106;
        const int WM_SYSKEYDOWN = 0x104;
        const int WM_SYSKEYUP = 0x105;
        const int WM_IME_CHAR = 0x286;

        private int _keysPressed = 0;
        protected override bool ProcessKeyMessage(ref Message m)
        {
            if (m.Msg == WM_KEYUP || m.Msg == WM_SYSKEYUP)
            {
                _keysPressed--;

                if (_keysPressed == 0)
                    OnHotkeyChanged(new EventArgs());
            }

            if (m.Msg != WM_CHAR && m.Msg != WM_SYSCHAR && m.Msg != WM_IME_CHAR)
            {
                KeyEventArgs e = new KeyEventArgs(((Keys)((int)((long)m.WParam))) | ModifierKeys);

                if (e.KeyCode == Keys.Delete || e.KeyCode == Keys.Back)
                    this.Reset();
                else
                {
                    // Print Screen doesn't seem to be part of WM_KEYDOWN/WM_SYSKEYDOWN...
                    if (m.Msg == WM_KEYDOWN || m.Msg == WM_SYSKEYDOWN || e.KeyCode == Keys.PrintScreen)
                    {
                        // Start over if we had no keys pressed, or have a selection (since it's always select all)
                        if (_keysPressed < 1 || SelectionLength > 0)
                            this.Reset();

                        //if (e.KeyCode )
                        //    this.Windows = true;

                        this.Control = !(e.Shift && e.Alt && !e.Control);
                        this.Shift = e.Shift;
                        this.Alt = e.Alt || (this.Control && !e.Shift); // Ctrl + Alt as default

                        if (e.KeyCode != Keys.ShiftKey
                            && e.KeyCode != Keys.ControlKey
                            && e.KeyCode != Keys.Menu)
                            this.KeyCode = e.KeyCode;

                        _keysPressed++;
                    }
                }
                
                // Pretty readable output
                RefreshText();

                // Select the end of our textbox
                Select(TextLength, 0);
            }

            return true;
        }
    }
}