pinvoke.net: Edit: user32.GetKeyboardState

@msdn=http://search.microsoft.com/search/results.aspx?qu=$$$
@pinvoke=http://pinvoke.net/$$$.htm

Summary: The GetKeyboardState API

!!!!C# Signature:
 [DllImport("user32.dll", SetLastError = true)]
 [return: MarshalAs(UnmanagedType.Bool)]
 static extern bool GetKeyboardState(byte [] lpKeyState);
!!!!VB Signature:
    <DllImport("user32.dll", SetLastError := true)> _
    Private Shared Function GetKeyboardState(ByVal keyState() As Byte) As Boolean
    End Function

'or...
 Private Declare Function GetKeyboardState Lib "user32" (ByVal keyState() As Byte) As Boolean
!!!!Notes:
In some cases this function will always return the same array, independent of actual keyboard state. This is due to Windows not updating the virtual key array internally. It has been found that declaring and calling GetKeyState on any key before calling GetKeyboardState will solve this issue.

!!!!Tips & Tricks:
Please add some!

!!!!Sample Code:

!!!!C#:

using System;
    using System.Runtime.InteropServices;
    using System.ComponentModel;

namespace PInvokeSample {
    	public static class Keyboard {

public static int GetKeyState(){
            	byte[] keys = new byte[256];

//Get pressed keys
            	if(!NativeMethods.GetKeyboardState(keys)){
                            int err = Marshal.GetLastWin32Error();
                            throw new Win32Exception(err);
            	}

for(int i = 0; i < 256; i++){

byte key = keys[i];

//Logical 'and' so we can drop the low-order bit for toggled keys, else that key will appear with the value 1!
                     if((key & 0x80) != 0){

//This is just for a short demo, you may want this to return
                        //multiple keys!
                    	return (int)key;
                     }
            	}
            	return -1;
              }
    	  }
    }

using System;
    using System.Runtime.InteropServices;

namespace PInvokeSample {
        internal static class NativeMethods {

[DllImport("User32.dll")]
            [return: MarshalAs(UnmanagedType.Bool)]
            internal static extern bool GetKeyboardState(byte[] lpKeyState);

}
     }

!!!!VB:

Imports System.Runtime.InteropServices

Public Class Form1

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Me.Text = "Caps:" & NativeMethods.CapsLockState.ToString
        Me.Text &= ", Num: " & NativeMethods.NumLockState.ToString
        Me.Text &= ", Scroll: " & NativeMethods.ScrollLockState.ToString
    End Sub

End Class

Public Class NativeMethods

Private Shared keyState() As Byte

<DllImport("user32.dll")> _
    Private Shared Function GetKeyboardState(ByVal keyState() As Byte) As Boolean
    End Function

Private Shared Sub Update()
        keyState = New Byte(256) {}
        Dim result As Boolean = GetKeyboardState(keyState)
        ' Check for error:
        If result = False Then
            Debug.WriteLine("GetKeyBoardState error: " & Marshal.GetLastWin32Error)
            Throw New Exception("GetKeyBoardState error: " & Marshal.GetLastWin32Error)
        End If
    End Sub

Public Enum LightState
        Off
        [On]
    End Enum

' Example - the keyboard lights...

Public Shared ReadOnly Property CapsLockState() As LightState
        Get
            Update()
            Dim isOn As Boolean = (keyState(Keys.CapsLock) = 1)
            Return IIf(isOn, LightState.On, LightState.Off)
        End Get
    End Property

Public Shared ReadOnly Property NumLockState() As LightState
        Get
            Update()
            Dim isOn As Boolean = (keyState(Keys.NumLock) = 1)
            Return IIf(isOn, LightState.On, LightState.Off)
        End Get
    End Property

Public Shared ReadOnly Property ScrollLockState() As LightState
        Get
            Update()
            Dim isOn As Boolean = (keyState(Keys.Scroll) = 1)
            Return IIf(isOn, LightState.On, LightState.Off)
        End Get
    End Property

End Class

!!!!Alternative Managed API:

using System;
	using System.Collections.Generic;
	using System.Runtime.InteropServices;
	using System.Text;

namespace PInvoke.Net
	{
		public class Keyboard
		{
			[DllImport( "user32.dll" )]
			static extern short GetKeyState( VirtualKeyStates nVirtKey );

public static bool IsKeyPressed( VirtualKeyStates testKey )
			{
				bool keyPressed = false;
				short result = GetKeyState( testKey );

switch( result )
				{
					case 0:
					// Not pressed and not toggled on.
					keyPressed = false;
					break;

case 1:
					// Not pressed, but toggled on
					keyPressed = false;
					break;

default:
					// Pressed (and may be toggled on)
					keyPressed = true;
					break;
				}

return keyPressed;
			}

public enum VirtualKeyStates : int
			{
				VK_LBUTTON = 0x01,
				VK_RBUTTON = 0x02,
				VK_CANCEL = 0x03,
				VK_MBUTTON = 0x04,
				//
				VK_XBUTTON1 = 0x05,
				VK_XBUTTON2 = 0x06,
				//
				VK_BACK = 0x08,
				VK_TAB = 0x09,
				//
				VK_CLEAR = 0x0C,
				VK_RETURN = 0x0D,
				//
				VK_SHIFT = 0x10,
				VK_CONTROL = 0x11,
				VK_MENU = 0x12,
				VK_PAUSE = 0x13,
				VK_CAPITAL = 0x14,
				//
				VK_KANA = 0x15,
				VK_HANGEUL = 0x15, /* old name - should be here for compatibility */
				VK_HANGUL = 0x15,
				VK_JUNJA = 0x17,
				VK_FINAL = 0x18,
				VK_HANJA = 0x19,
				VK_KANJI = 0x19,
				//
				VK_ESCAPE = 0x1B,
				//
				VK_CONVERT = 0x1C,
				VK_NONCONVERT = 0x1D,
				VK_ACCEPT = 0x1E,
				VK_MODECHANGE = 0x1F,
				//
				VK_SPACE = 0x20,
				VK_PRIOR = 0x21,
				VK_NEXT = 0x22,
				VK_END = 0x23,
				VK_HOME = 0x24,
				VK_LEFT = 0x25,
				VK_UP = 0x26,
				VK_RIGHT = 0x27,
				VK_DOWN = 0x28,
				VK_SELECT = 0x29,
				VK_PRINT = 0x2A,
				VK_EXECUTE = 0x2B,
				VK_SNAPSHOT = 0x2C,
				VK_INSERT = 0x2D,
				VK_DELETE = 0x2E,
				VK_HELP = 0x2F,
				//
				VK_LWIN = 0x5B,
				VK_RWIN = 0x5C,
				VK_APPS = 0x5D,
				//
				VK_SLEEP = 0x5F,
				//
				VK_NUMPAD0 = 0x60,
				VK_NUMPAD1 = 0x61,
				VK_NUMPAD2 = 0x62,
				VK_NUMPAD3 = 0x63,
				VK_NUMPAD4 = 0x64,
				VK_NUMPAD5 = 0x65,
				VK_NUMPAD6 = 0x66,
				VK_NUMPAD7 = 0x67,
				VK_NUMPAD8 = 0x68,
				VK_NUMPAD9 = 0x69,
				VK_MULTIPLY = 0x6A,
				VK_ADD = 0x6B,
				VK_SEPARATOR = 0x6C,
				VK_SUBTRACT = 0x6D,
				VK_DECIMAL = 0x6E,
				VK_DIVIDE = 0x6F,
				VK_F1 = 0x70,
				VK_F2 = 0x71,
				VK_F3 = 0x72,
				VK_F4 = 0x73,
				VK_F5 = 0x74,
				VK_F6 = 0x75,
				VK_F7 = 0x76,
				VK_F8 = 0x77,
				VK_F9 = 0x78,
				VK_F10 = 0x79,
				VK_F11 = 0x7A,
				VK_F12 = 0x7B,
				VK_F13 = 0x7C,
				VK_F14 = 0x7D,
				VK_F15 = 0x7E,
				VK_F16 = 0x7F,
				VK_F17 = 0x80,
				VK_F18 = 0x81,
				VK_F19 = 0x82,
				VK_F20 = 0x83,
				VK_F21 = 0x84,
				VK_F22 = 0x85,
				VK_F23 = 0x86,
				VK_F24 = 0x87,
				//
				VK_NUMLOCK = 0x90,
				VK_SCROLL = 0x91,
				//
				VK_OEM_NEC_EQUAL = 0x92, // '=' key on numpad
				//
				VK_OEM_FJ_JISHO = 0x92, // 'Dictionary' key
				VK_OEM_FJ_MASSHOU = 0x93, // 'Unregister word' key
				VK_OEM_FJ_TOUROKU = 0x94, // 'Register word' key
				VK_OEM_FJ_LOYA = 0x95, // 'Left OYAYUBI' key
				VK_OEM_FJ_ROYA = 0x96, // 'Right OYAYUBI' key
				//
				VK_LSHIFT = 0xA0,
				VK_RSHIFT = 0xA1,
				VK_LCONTROL = 0xA2,
				VK_RCONTROL = 0xA3,
				VK_LMENU = 0xA4,
				VK_RMENU = 0xA5,
				//
				VK_BROWSER_BACK = 0xA6,
				VK_BROWSER_FORWARD = 0xA7,
				VK_BROWSER_REFRESH = 0xA8,
				VK_BROWSER_STOP = 0xA9,
				VK_BROWSER_SEARCH = 0xAA,
				VK_BROWSER_FAVORITES = 0xAB,
				VK_BROWSER_HOME = 0xAC,
				//
				VK_VOLUME_MUTE = 0xAD,
				VK_VOLUME_DOWN = 0xAE,
				VK_VOLUME_UP = 0xAF,
				VK_MEDIA_NEXT_TRACK = 0xB0,
				VK_MEDIA_PREV_TRACK = 0xB1,
				VK_MEDIA_STOP = 0xB2,
				VK_MEDIA_PLAY_PAUSE = 0xB3,
				VK_LAUNCH_MAIL = 0xB4,
				VK_LAUNCH_MEDIA_SELECT = 0xB5,
				VK_LAUNCH_APP1 = 0xB6,
				VK_LAUNCH_APP2 = 0xB7,
				//
				VK_OEM_1 = 0xBA, // ';:' for US
				VK_OEM_PLUS = 0xBB, // '+' any country
				VK_OEM_COMMA = 0xBC, // ',' any country
				VK_OEM_MINUS = 0xBD, // '-' any country
				VK_OEM_PERIOD = 0xBE, // '.' any country
				VK_OEM_2 = 0xBF, // '/?' for US
				VK_OEM_3 = 0xC0, // '`~' for US
				//
				VK_OEM_4 = 0xDB, // '[{' for US
				VK_OEM_5 = 0xDC, // '\|' for US
				VK_OEM_6 = 0xDD, // ']}' for US
				VK_OEM_7 = 0xDE, // ''"' for US
				VK_OEM_8 = 0xDF,
				//
				VK_OEM_AX = 0xE1, // 'AX' key on Japanese AX kbd
				VK_OEM_102 = 0xE2, // "<>" or "\|" on RT 102-key kbd.
				VK_ICO_HELP = 0xE3, // Help key on ICO
				VK_ICO_00 = 0xE4, // 00 key on ICO
				//
				VK_PROCESSKEY = 0xE5,
				//
				VK_ICO_CLEAR = 0xE6,
				//
				VK_PACKET = 0xE7,
				//
				VK_OEM_RESET = 0xE9,
				VK_OEM_JUMP = 0xEA,
				VK_OEM_PA1 = 0xEB,
				VK_OEM_PA2 = 0xEC,
				VK_OEM_PA3 = 0xED,
				VK_OEM_WSCTRL = 0xEE,
				VK_OEM_CUSEL = 0xEF,
				VK_OEM_ATTN = 0xF0,
				VK_OEM_FINISH = 0xF1,
				VK_OEM_COPY = 0xF2,
				VK_OEM_AUTO = 0xF3,
				VK_OEM_ENLW = 0xF4,
				VK_OEM_BACKTAB = 0xF5,
				//
				VK_ATTN = 0xF6,
				VK_CRSEL = 0xF7,
				VK_EXSEL = 0xF8,
				VK_EREOF = 0xF9,
				VK_PLAY = 0xFA,
				VK_ZOOM = 0xFB,
				VK_NONAME = 0xFC,
				VK_PA1 = 0xFD,
				VK_OEM_CLEAR = 0xFE
			}
		}
	}

Documentation: GetKeyboardState@msdn on MSDN