Send keys through SendInput in user32.dll

Question

I am using this board as a keyboard for demo purposes.

Anyways to make the long story short everything works fine except for very few cases. I send keystrokes with the SendInput function located in user32.dll.

So my program looks like:

static void Main(string[] args)
{
    Console.Write("Press enter an on the next secont the key combination shift+end will be send");
    Console.Read();

    Thread.Sleep(1000);

    SendKeyDown(KeyCode.SHIFT);
    SendKeyPress(KeyCode.END);
    SendKeyUp(KeyCode.SHIFT);

    Console.Read(); 
    Console.Read();
}

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

/// <summary>
/// simulate key press
/// </summary>
/// <param name="keyCode"></param>
public static void SendKeyPress(KeyCode keyCode)
{
    INPUT input = new INPUT {
        Type = 1
    };
    input.Data.Keyboard = new KEYBDINPUT() {
        Vk = (ushort)keyCode,
        Scan = 0,
        Flags = 0,
        Time = 0,
        ExtraInfo = IntPtr.Zero,
    };

    INPUT input2 = new INPUT {
        Type = 1
    };
    input2.Data.Keyboard = new KEYBDINPUT() {
        Vk = (ushort)keyCode,
        Scan = 0,
        Flags = 2,
        Time = 0,
        ExtraInfo = IntPtr.Zero
    };
    INPUT[] inputs = new INPUT[] { input, input2 };
    if (SendInput(2, inputs, Marshal.SizeOf(typeof(INPUT))) == 0)
        throw new Exception();            
}

/// <summary>
/// Send a key down and hold it down until sendkeyup method is called
/// </summary>
/// <param name="keyCode"></param>
public static void SendKeyDown(KeyCode keyCode)
{
    INPUT input = new INPUT{
        Type = 1
    };
    input.Data.Keyboard = new KEYBDINPUT();
    input.Data.Keyboard.Vk = (ushort)keyCode;
    input.Data.Keyboard.Scan = 0;
    input.Data.Keyboard.Flags = 0;
    input.Data.Keyboard.Time = 0;
    input.Data.Keyboard.ExtraInfo = IntPtr.Zero;
    INPUT[] inputs = new INPUT[] { input };
    if (SendInput(1, inputs, Marshal.SizeOf(typeof(INPUT))) == 0)
    {
        throw new Exception();
    }
}

/// <summary>
/// Release a key that is being hold down
/// </summary>
/// <param name="keyCode"></param>
public static void SendKeyUp(KeyCode keyCode)
{
    INPUT input = new INPUT {
        Type = 1
    };
    input.Data.Keyboard = new KEYBDINPUT();
    input.Data.Keyboard.Vk = (ushort)keyCode;
    input.Data.Keyboard.Scan = 0;
    input.Data.Keyboard.Flags = 2;
    input.Data.Keyboard.Time = 0;
    input.Data.Keyboard.ExtraInfo = IntPtr.Zero;
    INPUT[] inputs = new INPUT[] { input };
    if (SendInput(1, inputs, Marshal.SizeOf(typeof(INPUT))) == 0)
        throw new Exception();

}

And here are the structs that I found online that those methods use and also the key codes: (note it looks like a lot of code and is because there are a lot of key codes in an Enum)

    /// <summary>
    /// http://msdn.microsoft.com/en-us/library/windows/desktop/ms646270(v=vs.85).aspx
    /// </summary>
    [StructLayout(LayoutKind.Sequential)]
    internal struct INPUT
    {
        public uint Type;
        public MOUSEKEYBDHARDWAREINPUT Data;
    }

    /// <summary>
    /// http://social.msdn.microsoft.com/Forums/en/csharplanguage/thread/f0e82d6e-4999-4d22-b3d3-32b25f61fb2a
    /// </summary>
    [StructLayout(LayoutKind.Explicit)]
    internal struct MOUSEKEYBDHARDWAREINPUT
    {
        [FieldOffset(0)]
        public HARDWAREINPUT Hardware;
        [FieldOffset(0)]
        public KEYBDINPUT Keyboard;
        [FieldOffset(0)]
        public MOUSEINPUT Mouse;
    }

    /// <summary>
    /// http://msdn.microsoft.com/en-us/library/windows/desktop/ms646310(v=vs.85).aspx
    /// </summary>
    [StructLayout(LayoutKind.Sequential)]
    internal struct HARDWAREINPUT
    {
        public uint Msg;
        public ushort ParamL;
        public ushort ParamH;
    }

    /// <summary>
    /// http://msdn.microsoft.com/en-us/library/windows/desktop/ms646310(v=vs.85).aspx
    /// </summary>
    [StructLayout(LayoutKind.Sequential)]
    internal struct KEYBDINPUT
    {
        public ushort Vk;
        public ushort Scan;
        public uint Flags;
        public uint Time;
        public IntPtr ExtraInfo;
    }

    /// <summary>
    /// http://social.msdn.microsoft.com/forums/en-US/netfxbcl/thread/2abc6be8-c593-4686-93d2-89785232dacd
    /// </summary>
    [StructLayout(LayoutKind.Sequential)]
    internal struct MOUSEINPUT
    {
        public int X;
        public int Y;
        public uint MouseData;
        public uint Flags;
        public uint Time;
        public IntPtr ExtraInfo;
    }

    public enum KeyCode : ushort
    {
        #region Media

        /// <summary>
        /// Next track if a song is playing
        /// </summary>
        MEDIA_NEXT_TRACK = 0xb0,

        /// <summary>
        /// Play pause
        /// </summary>
        MEDIA_PLAY_PAUSE = 0xb3,

        /// <summary>
        /// Previous track
        /// </summary>
        MEDIA_PREV_TRACK = 0xb1,

        /// <summary>
        /// Stop
        /// </summary>
        MEDIA_STOP = 0xb2,

        #endregion

        #region math

        /// <summary>Key "+"</summary>
        ADD = 0x6b,
        /// <summary>
        /// "*" key
        /// </summary>
        MULTIPLY = 0x6a,

        /// <summary>
        /// "/" key
        /// </summary>
        DIVIDE = 0x6f,

        /// <summary>
        /// Subtract key "-"
        /// </summary>
        SUBTRACT = 0x6d,

        #endregion

        #region Browser
        /// <summary>
        /// Go Back
        /// </summary>
        BROWSER_BACK = 0xa6,
        /// <summary>
        /// Favorites
        /// </summary>
        BROWSER_FAVORITES = 0xab,
        /// <summary>
        /// Forward
        /// </summary>
        BROWSER_FORWARD = 0xa7,
        /// <summary>
        /// Home
        /// </summary>
        BROWSER_HOME = 0xac,
        /// <summary>
        /// Refresh
        /// </summary>
        BROWSER_REFRESH = 0xa8,
        /// <summary>
        /// browser search
        /// </summary>
        BROWSER_SEARCH = 170,
        /// <summary>
        /// Stop
        /// </summary>
        BROWSER_STOP = 0xa9,
        #endregion

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

        #endregion

        #region Fkeys
        /// <summary>
        /// F1
        /// </summary>
        F1 = 0x70,
        /// <summary>
        /// F10
        /// </summary>
        F10 = 0x79,
        /// <summary>
        /// 
        /// </summary>
        F11 = 0x7a,
        /// <summary>
        /// 
        /// </summary>
        F12 = 0x7b,
        /// <summary>
        /// 
        /// </summary>
        F13 = 0x7c,
        /// <summary>
        /// 
        /// </summary>
        F14 = 0x7d,
        /// <summary>
        /// 
        /// </summary>
        F15 = 0x7e,
        /// <summary>
        /// 
        /// </summary>
        F16 = 0x7f,
        /// <summary>
        /// 
        /// </summary>
        F17 = 0x80,
        /// <summary>
        /// 
        /// </summary>
        F18 = 0x81,
        /// <summary>
        /// 
        /// </summary>
        F19 = 130,
        /// <summary>
        /// 
        /// </summary>
        F2 = 0x71,
        /// <summary>
        /// 
        /// </summary>
        F20 = 0x83,
        /// <summary>
        /// 
        /// </summary>
        F21 = 0x84,
        /// <summary>
        /// 
        /// </summary>
        F22 = 0x85,
        /// <summary>
        /// 
        /// </summary>
        F23 = 0x86,
        /// <summary>
        /// 
        /// </summary>
        F24 = 0x87,
        /// <summary>
        /// 
        /// </summary>
        F3 = 0x72,
        /// <summary>
        /// 
        /// </summary>
        F4 = 0x73,
        /// <summary>
        /// 
        /// </summary>
        F5 = 0x74,
        /// <summary>
        /// 
        /// </summary>
        F6 = 0x75,
        /// <summary>
        /// 
        /// </summary>
        F7 = 0x76,
        /// <summary>
        /// 
        /// </summary>
        F8 = 0x77,
        /// <summary>
        /// 
        /// </summary>
        F9 = 120,

        #endregion

        #region Other
        /// <summary>
        /// 
        /// </summary>
        OEM_1 = 0xba,
        /// <summary>
        /// 
        /// </summary>
        OEM_102 = 0xe2,
        /// <summary>
        /// 
        /// </summary>
        OEM_2 = 0xbf,
        /// <summary>
        /// 
        /// </summary>
        OEM_3 = 0xc0,
        /// <summary>
        /// 
        /// </summary>
        OEM_4 = 0xdb,
        /// <summary>
        /// 
        /// </summary>
        OEM_5 = 220,
        /// <summary>
        /// 
        /// </summary>
        OEM_6 = 0xdd,
        /// <summary>
        /// 
        /// </summary>
        OEM_7 = 0xde,
        /// <summary>
        /// 
        /// </summary>
        OEM_8 = 0xdf,
        /// <summary>
        /// 
        /// </summary>
        OEM_CLEAR = 0xfe,
        /// <summary>
        /// 
        /// </summary>
        OEM_COMMA = 0xbc,
        /// <summary>
        /// 
        /// </summary>
        OEM_MINUS = 0xbd,
        /// <summary>
        /// 
        /// </summary>
        OEM_PERIOD = 190,
        /// <summary>
        /// 
        /// </summary>
        OEM_PLUS = 0xbb,

        #endregion

        #region KEYS

        /// <summary>
        /// 
        /// </summary>
        KEY_0 = 0x30,
        /// <summary>
        /// 
        /// </summary>
        KEY_1 = 0x31,
        /// <summary>
        /// 
        /// </summary>
        KEY_2 = 50,
        /// <summary>
        /// 
        /// </summary>
        KEY_3 = 0x33,
        /// <summary>
        /// 
        /// </summary>
        KEY_4 = 0x34,
        /// <summary>
        /// 
        /// </summary>
        KEY_5 = 0x35,
        /// <summary>
        /// 
        /// </summary>
        KEY_6 = 0x36,
        /// <summary>
        /// 
        /// </summary>
        KEY_7 = 0x37,
        /// <summary>
        /// 
        /// </summary>
        KEY_8 = 0x38,
        /// <summary>
        /// 
        /// </summary>
        KEY_9 = 0x39,
        /// <summary>
        /// 
        /// </summary>
        KEY_A = 0x41,
        /// <summary>
        /// 
        /// </summary>
        KEY_B = 0x42,
        /// <summary>
        /// 
        /// </summary>
        KEY_C = 0x43,
        /// <summary>
        /// 
        /// </summary>
        KEY_D = 0x44,
        /// <summary>
        /// 
        /// </summary>
        KEY_E = 0x45,
        /// <summary>
        /// 
        /// </summary>
        KEY_F = 70,
        /// <summary>
        /// 
        /// </summary>
        KEY_G = 0x47,
        /// <summary>
        /// 
        /// </summary>
        KEY_H = 0x48,
        /// <summary>
        /// 
        /// </summary>
        KEY_I = 0x49,
        /// <summary>
        /// 
        /// </summary>
        KEY_J = 0x4a,
        /// <summary>
        /// 
        /// </summary>
        KEY_K = 0x4b,
        /// <summary>
        /// 
        /// </summary>
        KEY_L = 0x4c,
        /// <summary>
        /// 
        /// </summary>
        KEY_M = 0x4d,
        /// <summary>
        /// 
        /// </summary>
        KEY_N = 0x4e,
        /// <summary>
        /// 
        /// </summary>
        KEY_O = 0x4f,
        /// <summary>
        /// 
        /// </summary>
        KEY_P = 80,
        /// <summary>
        /// 
        /// </summary>
        KEY_Q = 0x51,
        /// <summary>
        /// 
        /// </summary>
        KEY_R = 0x52,
        /// <summary>
        /// 
        /// </summary>
        KEY_S = 0x53,
        /// <summary>
        /// 
        /// </summary>
        KEY_T = 0x54,
        /// <summary>
        /// 
        /// </summary>
        KEY_U = 0x55,
        /// <summary>
        /// 
        /// </summary>
        KEY_V = 0x56,
        /// <summary>
        /// 
        /// </summary>
        KEY_W = 0x57,
        /// <summary>
        /// 
        /// </summary>
        KEY_X = 0x58,
        /// <summary>
        /// 
        /// </summary>
        KEY_Y = 0x59,
        /// <summary>
        /// 
        /// </summary>
        KEY_Z = 90,

        #endregion

        #region volume
        /// <summary>
        /// Decrese volume
        /// </summary>
        VOLUME_DOWN = 0xae,

        /// <summary>
        /// Mute volume
        /// </summary>
        VOLUME_MUTE = 0xad,

        /// <summary>
        /// Increase volue
        /// </summary>
        VOLUME_UP = 0xaf,

        #endregion


        /// <summary>
        /// Take snapshot of the screen and place it on the clipboard
        /// </summary>
        SNAPSHOT = 0x2c,

        /// <summary>Send right click from keyboard "key that is 2 keys to the right of space bar"</summary>
        RightClick = 0x5d,

        /// <summary>
        /// Go Back or delete
        /// </summary>
        BACKSPACE = 8,

        /// <summary>
        /// Control + Break "When debuging if you step into an infinite loop this will stop debug"
        /// </summary>
        CANCEL = 3,
        /// <summary>
        /// Caps lock key to send cappital letters
        /// </summary>
        CAPS_LOCK = 20,
        /// <summary>
        /// Ctlr key
        /// </summary>
        CONTROL = 0x11,

        /// <summary>
        /// Alt key
        /// </summary>
        ALT = 18,

        /// <summary>
        /// "." key
        /// </summary>
        DECIMAL = 110,

        /// <summary>
        /// Delete Key
        /// </summary>
        DELETE = 0x2e,


        /// <summary>
        /// Arrow down key
        /// </summary>
        DOWN = 40,

        /// <summary>
        /// End key
        /// </summary>
        END = 0x23,

        /// <summary>
        /// Escape key
        /// </summary>
        ESC = 0x1b,

        /// <summary>
        /// Home key
        /// </summary>
        HOME = 0x24,

        /// <summary>
        /// Insert key
        /// </summary>
        INSERT = 0x2d,

        /// <summary>
        /// Open my computer
        /// </summary>
        LAUNCH_APP1 = 0xb6,
        /// <summary>
        /// Open calculator
        /// </summary>
        LAUNCH_APP2 = 0xb7,

        /// <summary>
        /// Open default email in my case outlook
        /// </summary>
        LAUNCH_MAIL = 180,

        /// <summary>
        /// Opend default media player (itunes, winmediaplayer, etc)
        /// </summary>
        LAUNCH_MEDIA_SELECT = 0xb5,

        /// <summary>
        /// Left control
        /// </summary>
        LCONTROL = 0xa2,

        /// <summary>
        /// Left arrow
        /// </summary>
        LEFT = 0x25,

        /// <summary>
        /// Left shift
        /// </summary>
        LSHIFT = 160,

        /// <summary>
        /// left windows key
        /// </summary>
        LWIN = 0x5b,


        /// <summary>
        /// Next "page down"
        /// </summary>
        PAGEDOWN = 0x22,

        /// <summary>
        /// Num lock to enable typing numbers
        /// </summary>
        NUMLOCK = 0x90,

        /// <summary>
        /// Page up key
        /// </summary>
        PAGE_UP = 0x21,

        /// <summary>
        /// Right control
        /// </summary>
        RCONTROL = 0xa3,

        /// <summary>
        /// Return key
        /// </summary>
        ENTER = 13,

        /// <summary>
        /// Right arrow key
        /// </summary>
        RIGHT = 0x27,

        /// <summary>
        /// Right shift
        /// </summary>
        RSHIFT = 0xa1,

        /// <summary>
        /// Right windows key
        /// </summary>
        RWIN = 0x5c,

        /// <summary>
        /// Shift key
        /// </summary>
        SHIFT = 0x10,

        /// <summary>
        /// Space back key
        /// </summary>
        SPACE_BAR = 0x20,

        /// <summary>
        /// Tab key
        /// </summary>
        TAB = 9,

        /// <summary>
        /// Up arrow key
        /// </summary>
        UP = 0x26,

    }

So now my question is why when I send that key combination I do not get the same results as when I do it on a real keyboard? 98% of the things work. For example I am able to do:

    SendKeyDown(KeyCode.SHIFT);
    SendKeyPress(KeyCode.KEY_A );
    SendKeyUp(KeyCode.SHIFT);

And that will send a capital A.

Should I use a different library?

The reason why I like this approach is because I do not know in advance if the user will send a key combination For example in windows forms If I do:

System.Windows.Forms.SendKeys.SendWait("+{end}"); that will send shift + end but maybe the user just wants to send shift...

Solution 1

You aren't setting the flags and scan fields, depending on the keystrokes desired, you will need to set these correctly to get the OS to recognize the keys correctly.

You might consider using the Input Simulator library, since it already does what you want and you don't have to recreate the wheel. Just make sure to look through the forums as there are some good patches in there that need to be set, since the author abandoned the project in 2009. It's a good library nonetheless.

Solution 2

Another way of sending keyboard input to a window (I use this for UI testing) is to use the Unicode alternative in KEYBDINPUT which saves you from mapping each character to the virtual key:

public static void SendString(string inputStr)
{
    var hWnd = System.Diagnostics.Process.GetCurrentProcess().MainWindowHandle;
    WinAPI.SetForegroundWindow(hWnd);           
    List<WinAPI.INPUT> keyList = new List<WinAPI.INPUT>();
    foreach (short c in inputStr)
    {
        switch (c)
        {
            case 8: // Translate \t to VK_TAB
                {
                    WinAPI.INPUT keyDown = new WinAPI.INPUT();
                    keyDown.type = 1; //Keyboard
                    keyDown.union.keyboardInput.wVk = (short)WinAPI.WindowsVirtualKey.VK_TAB;
                    keyDown.union.keyboardInput.dwFlags = 0;
                    keyDown.union.keyboardInput.wScan = 0; //use VirtualKey
                    keyList.Add(keyDown);
                    WinAPI.INPUT keyUp = new WinAPI.INPUT();
                    keyUp.type = 1; //Keyboard
                    keyUp.union.keyboardInput.wVk = (short)WinAPI.WindowsVirtualKey.VK_TAB;
                    keyUp.union.keyboardInput.dwFlags = 0x0002;
                    keyUp.union.keyboardInput.wScan = 0; //use VirtualKey
                    keyList.Add(keyUp);
                }
                break;
            case 10: // Translate \n to VK_RETURN
                {
                    WinAPI.INPUT keyDown = new WinAPI.INPUT();
                    keyDown.type = 1; //Keyboard
                    keyDown.union.keyboardInput.wVk = (short)WinAPI.WindowsVirtualKey.VK_RETURN;
                    keyDown.union.keyboardInput.dwFlags = 0;
                    keyDown.union.keyboardInput.wScan = 0; //use VirtualKey
                    keyList.Add(keyDown);
                    WinAPI.INPUT keyUp = new WinAPI.INPUT();
                    keyUp.type = 1; //Keyboard
                    keyUp.union.keyboardInput.wVk = (short)WinAPI.WindowsVirtualKey.VK_RETURN;
                    keyUp.union.keyboardInput.dwFlags = 0x0002; 
                    keyUp.union.keyboardInput.wScan = 0; //use VirtualKey
                    keyList.Add(keyUp);
                }
                break;                  
            default:
                {
                    WinAPI.INPUT keyDown = new WinAPI.INPUT();
                    keyDown.type = 1; //Keyboard
                    keyDown.union.keyboardInput.wVk = 0; //Use unicode
                    keyDown.union.keyboardInput.dwFlags = 0x0004; //Unicode Key Down
                    keyDown.union.keyboardInput.wScan = c;
                    keyList.Add(keyDown);
                    WinAPI.INPUT keyUp = new WinAPI.INPUT();
                    keyUp.type = 1; //Keyboard
                    keyUp.union.keyboardInput.wVk = 0; //Use unicode
                    keyUp.union.keyboardInput.dwFlags = 0x0004 | 0x0002; //Unicode Key Up
                    keyUp.union.keyboardInput.wScan = c;
                    keyList.Add(keyUp);
                }
                break;
        }
    }
    WinAPI.SendInput((uint)keyList.Count, keyList.ToArray(), Marshal.SizeOf(typeof(WinAPI.INPUT)));             
}

Solution 3

You could try this. It works for : Shift + A, Ctrl + LShiftv + S, Ctrl + A

The others I didn't try but I think you could send any key combination

public static void MultiKeyPress(KeyCode[] keys){
    INPUT[] inputs = new INPUT[keys.Count() * 2];
    for(int a = 0; a < keys.Count(); ++a){
        for(int b = 0; b < 2; ++b){
            inputs[(b == 0) ? a : inputs.Count() - 1 - a].Type = 1;
            inputs[(b == 0) ? a : inputs.Count() - 1 - a].Data.Keyboard = new KEYBDINPUT() {
                Vk = (ushort)keys[a],
                Scan = 0,
                Flags = Convert.ToUInt32((b == 0)?0:2),
                Time = 0,
                ExtraInfo = IntPtr.Zero,
            };
        }
    }
    if (SendInput(Convert.ToUInt32(inputs.Count()), inputs, Marshal.SizeOf(typeof(INPUT))) == 0)
        throw new Exception();
}

//call with this :
MultiKeyPress(new virtualInputs.KeyCode[] { KeyCode.LSHIFT, KeyCode.KEY_A });

/!\ the window that have the focus will get the keypress so you need to make sure the right window have the focus