Question

I’m writing a C# automation tool.

Since Microsoft UI Automation doesn’t provide any way of simulating right-clicks or raising context menus, I’m using SendMessage to do this instead. I’d rather not use SendInput because I don’t want to have to grab focus.

When I call SendMessage, however, it crashes the target app.

Here’s my code:

    [DllImport("user32.dll", CharSet = CharSet.Auto)]
    static extern IntPtr SendMessage(IntPtr hWnd, UInt32 Msg, IntPtr wParam, IntPtr lParam);

    public void RightClick<T>(T element) where T: AutomationElementWrapper
    {
        const int MOUSEEVENTF_RIGHTDOWN = 0x0008; /* right button down */
        const int MOUSEEVENTF_RIGHTUP = 0x0010; /* right button up */

        var point = element.Element.GetClickablePoint();
        var processId = element.Element.GetCurrentPropertyValue(AutomationElement.ProcessIdProperty);
        var window = AutomationElement.RootElement.FindFirst(
            TreeScope.Children,
            new PropertyCondition(AutomationElement.ProcessIdProperty,
                                  processId));
        var handle = window.Current.NativeWindowHandle;

        var x = point.X;
        var y = point.Y;

        var value = ((int)x)<<16 + (int)y;

        SendMessage(new IntPtr(handle), MOUSEEVENTF_RIGHTDOWN, IntPtr.Zero, new IntPtr(value));
        SendMessage(new IntPtr(handle), MOUSEEVENTF_RIGHTUP, IntPtr.Zero, new IntPtr(value));
    }

Any idea what I’m doing wrong?

Answer 1

You’re mixing up your types. You’re using SendMessage, which takes a window message (which by convention are named WM_…), but you’re passing it a MOUSEINPUT.dwFlags value that’s meant for SendInput (which are named MOUSEEVENTF_…). You’re basically passing gibberish.

What your code is actually doing is sending a window message whose numeric value is 8 (which, in window messages, means WM_KILLFOCUS), followed by a window message of 0x10 == 16 (WM_CLOSE). It’s the latter that’s likely causing you problems — you’re telling the window to close. I’m not sure why it would crash, but it would certainly exit.

If you’re using SendMessage, you need to pass it window messages (WM_, for example WM_RBUTTONDOWN and WM_RBUTTONUP).