Using the windows API to simulate keyboard input in C#

In the last artile, the basics of hardware input was discussed using the User32 api to drive mouse movement. The second part, keyboard input, is covered in this article.

To begin, the required structs and enumbs need to be defined - as well as the User32.dll call.

public enum KeyCode : ushort
{
	#region Media
	MEDIA_NEXT_TRACK = 0xb0,
	MEDIA_PREV_TRACK = 0xb1,
	MEDIA_STOP = 0xb2,
	MEDIA_PLAY_PAUSE = 0xb3,
	#endregion

	#region Math Functions
	MULTIPLY = 0x6a, // '*'
	ADD = 0x6b,
	SUBTRACT = 0x6d,
	DIVIDE = 0x6f,
	#endregion

	#region Browser
	BROWSER_BACK = 0xa6,
	BROWSER_FORWARD = 0xa7,
	BROWSER_REFRESH = 0xa8,
	BROWSER_STOP = 0xa9,
	BROWSER_SEARCH = 0xaa,
	BROWSER_FAVORITES = 0xab,
	BROWSER_HOME = 0xac,
	#endregion

	#region Numpad numbers
	NUMPAD0 = 0x60,
	NUMPAD1 = 0x61,
	NUMPAD2 = 0x62,
	NUMPAD3 = 0x63,
	NUMPAD4 = 0x64, // 100
	NUMPAD5 = 0x65,
	NUMPAD6 = 0x66,
	NUMPAD7 = 0x67,
	NUMPAD8 = 0x68,
	NUMPAD9 = 0x69,
	#endregion

	#region Function Keys
	F1 = 0x70,
	F2 = 0x71,
	F3 = 0x72,
	F4 = 0x73,
	F5 = 0x74,
	F6 = 0x75,
	F7 = 0x76,
	F8 = 0x77,
	F9 = 0x78,
	F10 = 0x79,
	F11 = 0x7a,
	F12 = 0x7b,
	F13 = 0x7c,
	F14 = 0x7d,
	F15 = 0x7e,
	F16 = 0x7f,
	F17 = 0x80,
	F18 = 0x81,
	F19 = 130,
	F20 = 0x83,
	F21 = 0x84,
	F22 = 0x85,
	F23 = 0x86,
	F24 = 0x87,
	#endregion

	#region Other 
	// see https://lists.w3.org/Archives/Public/www-dom/2010JulSep/att-0182/keyCode-spec.html
	OEM_COLON = 0xba, // OEM_1
	OEM_102 = 0xe2,
	OEM_2 = 0xbf,
	OEM_3 = 0xc0,
	OEM_4 = 0xdb,
	OEM_BACK_SLASH = 0xdc, // OEM_5
	OEM_6 = 0xdd,
	OEM_7 = 0xde,
	OEM_8 = 0xdf,
	OEM_CLEAR = 0xfe,
	OEM_COMMA = 0xbc,
	OEM_MINUS = 0xbd, // Underscore
	OEM_PERIOD = 0xbe,
	OEM_PLUS = 0xbb,
	#endregion

	#region KEYS
	KEY_0 = 0x30,
	KEY_1 = 0x31,
	KEY_2 = 0x32,
	KEY_3 = 0x33,
	KEY_4 = 0x34,
	KEY_5 = 0x35,
	KEY_6 = 0x36,
	KEY_7 = 0x37,
	KEY_8 = 0x38,
	KEY_9 = 0x39,
	KEY_A = 0x41,
	KEY_B = 0x42,
	KEY_C = 0x43,
	KEY_D = 0x44,
	KEY_E = 0x45,
	KEY_F = 0x46,
	KEY_G = 0x47,
	KEY_H = 0x48,
	KEY_I = 0x49,
	KEY_J = 0x4a,
	KEY_K = 0x4b,
	KEY_L = 0x4c,
	KEY_M = 0x4d,
	KEY_N = 0x4e,
	KEY_O = 0x4f,
	KEY_P = 0x50,
	KEY_Q = 0x51,
	KEY_R = 0x52,
	KEY_S = 0x53,
	KEY_T = 0x54,
	KEY_U = 0x55,
	KEY_V = 0x56,
	KEY_W = 0x57,
	KEY_X = 0x58,
	KEY_Y = 0x59,
	KEY_Z = 0x5a,
	#endregion

	#region volume
	VOLUME_MUTE = 0xad,
	VOLUME_DOWN = 0xae,
	VOLUME_UP = 0xaf,
	#endregion

	SNAPSHOT = 0x2c,
	RIGHT_CLICK = 0x5d,
	BACKSPACE = 8,
	CANCEL = 3,
	CAPS_LOCK = 20,
	CONTROL = 0x11,
	ALT = 18,
	DECIMAL = 110,
	DELETE = 0x2e,
	DOWN = 40,
	END = 0x23,
	ESC = 0x1b,
	HOME = 0x24,
	INSERT = 0x2d,
	LAUNCH_APP1 = 0xb6,
	LAUNCH_APP2 = 0xb7,
	LAUNCH_MAIL = 180,
	LAUNCH_MEDIA_SELECT = 0xb5,
	LCONTROL = 0xa2,
	LEFT = 0x25,
	LSHIFT = 0xa0,
	LWIN = 0x5b,
	PAGEDOWN = 0x22,
	NUMLOCK = 0x90,
	PAGE_UP = 0x21,
	RCONTROL = 0xa3,
	ENTER = 13,
	RIGHT = 0x27,
	RSHIFT = 0xa1,
	RWIN = 0x5c,
	SHIFT = 0x10,
	SPACE_BAR = 0x20,
	TAB = 9,
	UP = 0x26,
}

[Flags]
public enum SendInputEventType : uint
{
	InputMouse,
	InputKeyboard,
	InputHardware
}

[StructLayout(LayoutKind.Sequential)]
public struct MOUSEINPUT
{
	public int dx;
	public int dy;
	public uint mouseData;
	public MouseEventFlags dwFlags;
	public uint time;
	public IntPtr dwExtraInfo;
}

[StructLayout(LayoutKind.Sequential)]
public struct KEYBOARDINPUT
{
	public ushort wVk;
	public ushort wScan;
	public uint dwFlags;
	public uint time;
	public IntPtr dwExtraInfo;
}

[StructLayout(LayoutKind.Sequential)]
public struct HARDWAREINPUT
{
	public int uMsg;
	public short wParamL;
	public short wParamH;
}

[StructLayout(LayoutKind.Explicit)]
public struct MOUSEANDKEYBOARDINPUT
{
	[FieldOffset(0)]
	public MOUSEINPUT mi;

	[FieldOffset(0)]
	public KEYBOARDINPUT ki;

	[FieldOffset(0)]
	public HARDWAREINPUT hi;
}

[StructLayout(LayoutKind.Sequential)]
public struct INPUT
{
	public SendInputEventType type;
	public MOUSEANDKEYBOARDINPUT mkhi;
}

[DllImport("user32.dll", SetLastError = true)]
public static extern uint SendInput(uint numberOfInputs, INPUT[] inputs, int sizeOfInputStructure);

Given these type defintions, we can build a KeyPress method.

public static void KeyPress(KeyCode keyCode) {
	INPUT input = new INPUT
	{
		type = SendInputEventType.InputKeyboard,
		mkhi = new MOUSEANDKEYBOARDINPUT
		{
			ki = new KEYBOARDINPUT
			{
				wVk = (ushort)keyCode,
				wScan = 0,
				dwFlags = 0, // if nothing, key down
				time = 0,
				dwExtraInfo = IntPtr.Zero,
			}
		} 
	};

	INPUT input2 = new INPUT
	{
		type = SendInputEventType.InputKeyboard,
		mkhi = new MOUSEANDKEYBOARDINPUT
		{
			ki = new KEYBOARDINPUT
			{
				wVk = (ushort)keyCode,
				wScan = 0,
				dwFlags = 2, // key up
				time = 0,
				dwExtraInfo = IntPtr.Zero,
			}
		}
	};

	INPUT[] inputs = new INPUT[] { input, input2 }; // Combined, it's a keystroke
	User32.SendInput((uint)inputs.Length, inputs, Marshal.SizeOf(typeof(INPUT)));
}

Now, we can command our keystrokes.

KeyPress(KeyCode.SHIFT);