winapi - How to send text to Notepad in C#/Win32?

Question

I'm trying to use SendMessage to Notepad, so that I can insert written text without making Notepad the active window.

I have done something like this in the past using SendText, but that required giving Notepad focus.

Now, first I'm retrieving the Windows handle:

Process[] processes = Process.GetProcessesByName("notepad");
Console.WriteLine(processes[0].MainWindowHandle.ToString());

I've confirmed it's the right handle for Notepad, the same shown within Windows Task Manager.

[DllImport("User32.dll", EntryPoint = "SendMessage")]
public static extern int SendMessage(int hWnd, int Msg, int wParam, int lParam);

From here, I haven't been able to get SendMessage to work in all my experimentation. Am I going in the wrong direction?

Answer 1

    [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);
    private void button1_Click(object sender, EventArgs e)
    {
        Process [] notepads=Process.GetProcessesByName("notepad");
        if(notepads.Length==0)return;            
        if (notepads[0] != null)
        {
            IntPtr child= FindWindowEx(notepads[0].MainWindowHandle, new IntPtr(0), "Edit", null);
            SendMessage(child, 0x000C, 0, textBox1.Text);
        }
    }

WM_SETTEXT=0x000c