C# - Add/Send text to notepad process using user32.dll SendMessage from your application

Post date: Jan 13, 2012 9:31:37 AM

How to add text to another applications text fields from your application?

This is a simple example of starting a Notepad process and then adding text to it.

Will open a new Notepad.exe process and then add the text "Sending a message, a message from me to you" to the text area of notepad.

The constant 0x000c of SendMessage is documented here http://msdn.microsoft.com/en-us/library/windows/desktop/ms632644(v=vs.85).aspx .

The constant says SETTEXT which really means that the text in notepad will be replaced if you send more than one message using this constant.

using System;using System.Text;using System.Runtime.InteropServices;using System.Diagnostics;namespace SendMessageTest { class Program { [DllImport("user32.dll", EntryPoint = "FindWindowEx")] public static extern IntPtr FindWindowEx(IntPtr hwndParent, IntPtr hwndChildAfter, string lpszClass, string lpszWindow); [DllImport("User32.dll")] public static extern int SendMessage(IntPtr hWnd, int uMsg, int wParam, string lParam); static void Main(string[] args) { DoSendMessage("Sending a message, a message from me to you"); } private static void DoSendMessage(string message) { Process notepad = Process.Start(new ProcessStartInfo("notepad.exe")); notepad.WaitForInputIdle(); if (notepad != null) { IntPtr child = FindWindowEx(notepad.MainWindowHandle, new IntPtr(0), "Edit", null); SendMessage(child, 0x000C, 0, message); } } }}