SendMessage stuck after button click

Question

Strange issue I can't put my finger on. Search for the main window, then I search for the button control with the caption "Start". After it finds start and sends the button click, it just sits and never gets past that so I never see "Leaving loop" in the console.

The button does get pressed and a message box pops up that I would continue to answer outside of this section of code. The odd thing is once I manually answer that box it then breaks past NativeMethods.SendMessage(start, BM_CLICK, IntPtr.Zero, ""); and I see "Leaving Loop" and then it's all happy and continues on it's way.

What am I missing here? Hope I explained this well enough.

while (!mainFound)
{
    hwnd = NativeMethods.FindWindow(null, "Loader");
    if (!hwnd.Equals(IntPtr.Zero))
    {
        Console.WriteLine("Found Main");

        IntPtr p = IntPtr.Zero;
        while (!mainFound)
        {
            hwndChild = NativeMethods.FindWindowEx(hwnd, p, null, null);
            if (hwndChild == IntPtr.Zero)
            {
                 break;
            }

            IntPtr start = NativeMethods.FindWindowEx(hwndChild, IntPtr.Zero, null, "Start");
            if (!start.Equals(IntPtr.Zero))
            {
                Console.WriteLine("Found Start");
                NativeMethods.SendMessage(start, BM_CLICK, IntPtr.Zero, "");
                Console.WriteLine("Leaving Loop");
                mainFound = true;
            }

             //Console.WriteLine(hwndChild);
             p = hwndChild;
       }
 }   

}

Answer 1

SendMessage is a synchronous call: it waits for the message to be processed before returning. From your description, it sounds like the handler for BM_CLICK displays a modal dialog, which means that SendMessage won't return until the modal dialog is dismissed.

Try PostMessage instead.