How do you get a child window using its control ID?

Question

I am new to WINAPI and have figured out how to send a message to another program. The program I am using however I would like to be able to have it click on a specific button. From what I have learned by viewing Spy++ windows handles change for the programs every time they are reloaded and so do the handles for their controls. The control ID stays the same. After two days of trying to figure it out I am here.

under SendMesssageA if I specify the current handle as viewable by Spy++ and use that and run the code it works fine and clicks the button on my external application. I am attempting to use GetDlgItem as I have read that I can get the handle for the control (child window) using it. I am doing something wrong however since no matter what I do it returns 0 or 'null'.

How can I get GetDlgItem to return the child control handle so that I may use it to sendmessage to click that control in the external application?

Thanks for your help an input ahead of time.

    [DllImport("User32.dll")]
    static extern bool SetForegroundWindow(IntPtr hWnd);
    Process[] myProcess = Process.GetProcessesByName("program name here");

    [DllImport("user32.dll", CharSet = CharSet.Auto)]
    static extern int SendMessageA(IntPtr hwnd, int wMsg, int wParam, uint lParam);

    [DllImport("user32.dll", CharSet = CharSet.Auto)]
    public static extern IntPtr GetDlgItem(int hwnd, int childID);

    public const int WM_LBUTTONDOWN = 0x0201;
    public const int WM_LBUTTONUP = 0x0202;


    public void SendClick()
    {
        IntPtr hwnd = myProcess[0].MainWindowHandle;
        SetForegroundWindow(hwnd);

        int intCID = 1389;
        IntPtr ptrTest = GetDlgItem(hwnd, intCID);
        SendKeys.SendWait(" ");
        Thread.Sleep(1000);
        SendKeys.SendWait("various text to be sent here");
        Thread.Sleep(1000);
        SendKeys.SendWait("{ENTER}");
        Thread.Sleep(1000);

        SendMessageA(ptrTest, WM_LBUTTONDOWN, WM_LBUTTONDOWN, 0);
    }

Answer 1

I think you have to use the Win32 API to find the "receiving" application window, and then find a child window of that handle. This is something I found googling Win32 API FindWindow

http://www.c-sharpcorner.com/UploadFile/shrijeetnair/win32api12062005005528AM/win32api.aspx