PostMessage example

Program.cs

using System.Diagnostics;
using System.Runtime.InteropServices;

class Program
{
    [DllImport("user32.dll", CharSet = CharSet.Auto)]
    public static extern IntPtr FindWindow(string className, string? windowName);

    [DllImport("user32.dll", CharSet = CharSet.Auto)]
    public static extern IntPtr FindWindowEx(IntPtr hwndParent, IntPtr hwndChildAfter, string lpszClass, string? lpszWindow);

    [DllImport("user32.dll", CharSet = CharSet.Auto)]
    public static extern bool SetForegroundWindow(IntPtr hWnd);

    [DllImport("user32.dll", CharSet = CharSet.Auto)]
    public static extern uint PostMessage(IntPtr hwnd, uint msg, IntPtr wParam, IntPtr lParam);

    const uint WM_CHAR = 0x0102;

    static void Main()
    {
        string notepadPath = @"C:\\Program Files\\Notepad++\\notepad++.exe";

        if (!File.Exists(notepadPath))
        {
            Console.WriteLine("Notepad++ не знайдений!");
            return;
        }

        Process.Start(notepadPath);
        Thread.Sleep(2000);

        IntPtr hwndNotepad = IntPtr.Zero;
        while (hwndNotepad == IntPtr.Zero)
        {
            hwndNotepad = FindWindow("Notepad++", null);
            Thread.Sleep(500);
        }

        if (hwndNotepad == IntPtr.Zero)
        {
            Console.WriteLine("Не знайдено вікно Notepad++.");
            return;
        }

        IntPtr hwndScintilla = IntPtr.Zero;
        while (hwndScintilla == IntPtr.Zero)
        {
            hwndScintilla = FindWindowEx(hwndNotepad, IntPtr.Zero, "Scintilla", null);
            Thread.Sleep(500);
        }

        if (hwndScintilla == IntPtr.Zero)
        {
            Console.WriteLine("Не знайдено текстове поле в Notepad++.");
            return;
        }

        SetForegroundWindow(hwndNotepad);
        Thread.Sleep(500);

        string textToSend = "Доброго вечора! Як справи?";
        foreach (char c in textToSend)
        {
            PostMessage(hwndScintilla, WM_CHAR, c, IntPtr.Zero);
            Thread.Sleep(50);
        }
    }
}