C # –Sample key input by SendInput (Windows API) (32 / 64bit compatible)

Reference site

• KEYBDINPUT structure - Microsoft Docs
• MapVirtualKeyA - Microsoft Docs
  -About keyboard pseudo operation by C #

Source code

using System;
using System.Drawing;
using System.Runtime.InteropServices;
using System.Threading;
using System.Threading.Tasks;
using System.Windows.Forms;

class MainForm : Form
{
    TextBox txt;

    MainForm()
    {
        Button btn = new Button(){
            Size = new Size(100,30),
            Text = "Test",
        };
        btn.Click += (s,e)=>{
            SendInputKeyPressAndRelease(Keys.Tab);
            SendInputKeyPressAndRelease(Keys.A);
        };
        Controls.Add(btn);


        txt = new TextBox(){
            Location = new Point(0, 30),
            Size = new Size(100,30),
            Text = "Test",
        };
        Controls.Add(txt);
    }

    private static class NativeMethods
    {
        [DllImport("user32.dll", SetLastError = true)]
        public extern static void SendInput(int nInputs, Input[] pInputs, int cbsize);

        [DllImport("user32.dll", EntryPoint = "MapVirtualKeyA")]
        public extern static int MapVirtualKey(int wCode, int wMapType);

        //[DllImport("user32.dll", SetLastError = true)]
        //public extern static IntPtr GetMessageExtraInfo();
    }

    [StructLayout(LayoutKind.Sequential)]
    private struct POINT
    {
        public int x;
        public int y;
    }

    [StructLayout(LayoutKind.Sequential)]
    struct MouseInput
    {
        public int X;
        public int Y;
        public int Data;
        public int Flags;
        public int Time;
        public IntPtr ExtraInfo;
    }

    [StructLayout(LayoutKind.Sequential)]
    struct KeyboardInput
    {
        public short VirtualKey;
        public short ScanCode;
        public int Flags;
        public int Time;
        public IntPtr ExtraInfo;
    }

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

    [StructLayout(LayoutKind.Sequential)]
    struct Input
    {
        public int Type;
        public InputUnion ui;
    }

    [StructLayout(LayoutKind.Explicit)]
    struct InputUnion
    {
        [FieldOffset(0)]
        public MouseInput Mouse;
        [FieldOffset(0)]
        public KeyboardInput Keyboard;
        [FieldOffset(0)]
        public HardwareInput Hardware;
    }

    private const int KEYEVENTF_EXTENDEDKEY = 0x0001;
    private const int KEYEVENTF_KEYUP = 0x0002;
    private const int KEYEVENTF_SCANCODE = 0x0008;
    private const int KEYEVENTF_UNICODE = 0x0004;

    private const int MAPVK_VK_TO_VSC = 0;
    // private const int MAPVK_VSC_TO_VK = 1;

    void SendKeyInput()
    {
        BeginInvoke(
            (MethodInvoker)delegate(){
                SendInputKeyPressAndRelease(Keys.Tab);
            }
        );
    }

    private static void SendInputKeyPressAndRelease(Keys key)
    {
        Input[] inputs = new Input[2];

        int vsc = NativeMethods.MapVirtualKey((int)key, MAPVK_VK_TO_VSC);

        inputs[0] = new Input();
        inputs[0].Type = 1; // KeyBoard = 1
        inputs[0].ui.Keyboard.VirtualKey = (short)key;
        inputs[0].ui.Keyboard.ScanCode = (short)vsc;
        inputs[0].ui.Keyboard.Flags = 0;
        inputs[0].ui.Keyboard.Time = 0;
        inputs[0].ui.Keyboard.ExtraInfo = IntPtr.Zero;

        inputs[1] = new Input();
        inputs[1].Type = 1; // KeyBoard = 1
        inputs[1].ui.Keyboard.VirtualKey = (short)key;
        inputs[1].ui.Keyboard.ScanCode = (short)vsc;
        inputs[1].ui.Keyboard.Flags = KEYEVENTF_KEYUP;
        inputs[1].ui.Keyboard.Time = 0;
        inputs[1].ui.Keyboard.ExtraInfo = IntPtr.Zero;

        NativeMethods.SendInput(inputs.Length, inputs, Marshal.SizeOf(inputs[0]));
    }


    [STAThread]
    static void Main(string[] args)
    {
        Application.Run(new MainForm());
    }
}