C # –Send a multibyte string with SendInput

Background

I didn’t like the behavior of the unformatted copy of MS Word (it takes a lot of extra care peculiar to MS Office), so let’s create a program material that allows you to enter plain text by simulating keystrokes. I thought.

capture

When you press the Send text button, the countdown starts, and after 6 seconds, the character string in the text box directly below is sent by Send Input. (During the countdown, focus on the window or control you want SendInput to flow into.)

• Depending on the recipient, it may not be supported.
  By the way, in Word, the behavior seems to change depending on the state of IME. (In the “A” (full-width) state, the conversion candidate is selected after SendInput is performed.)

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;
    Button btn;
    System.Windows.Forms.Timer tmr;
    int _counter;

    MainForm()
    {
        _counter = 0;

        tmr = new System.Windows.Forms.Timer();
        tmr.Interval = 200;
        tmr.Tick += (s,e)=>{
            if ( _counter > 0 ) {
                _counter--;
                int inMsec = _counter * tmr.Interval;
                Text = (inMsec/1000).ToString() + "." + ((inMsec%1000)/100).ToString();
            }
            else{
                tmr.Stop();
                txt.ReadOnly = false;
                btn.Enabled = true;
                SendKeyInput(txt.Text);
            }
        };

        btn = new Button(){
            Size = new Size(100,30),
            Text = "Test",
        };
        btn.Click += (s,e)=>{
            txt.ReadOnly = true;
            btn.Enabled = false;
            if ( !tmr.Enabled ) {
                _counter = 30;
                tmr.Start();
            }
        };
        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(string s)
    {
        BeginInvoke(
            (MethodInvoker)delegate(){
                SendInputKeyPressAndRelease(s);
            }
        );
    }

    private static void SendInputKeyPressAndRelease(string s)
    {
        Input[] inputs = new Input[2*s.Length];

        for(int k=0; k<s.Length; k++) {
            int tk = s[k];
            //int vsc = NativeMethods.MapVirtualKey(tk, MAPVK_VK_TO_VSC);

            inputs[2*k] = new Input();
            inputs[2*k].Type = 1; // KeyBoard = 1
            inputs[2*k].ui.Keyboard.VirtualKey = 0;
            inputs[2*k].ui.Keyboard.ScanCode = (short)tk;
            inputs[2*k].ui.Keyboard.Flags = KEYEVENTF_UNICODE;
            inputs[2*k].ui.Keyboard.Time = 0;
            inputs[2*k].ui.Keyboard.ExtraInfo = IntPtr.Zero;

            inputs[2*k+1] = new Input();
            inputs[2*k+1].Type = 1; // KeyBoard = 1
            inputs[2*k+1].ui.Keyboard.VirtualKey = 0;
            inputs[2*k+1].ui.Keyboard.ScanCode = (short)tk;
            inputs[2*k+1].ui.Keyboard.Flags = KEYEVENTF_UNICODE | KEYEVENTF_KEYUP;
            inputs[2*k+1].ui.Keyboard.Time = 0;
            inputs[2*k+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());
    }
}

Reference site

https://docs.microsoft.com/en-us/windows/win32/api/winuser/ns-winuser-keybdinput