I had a baffling problem arise today. Here is the scenario; I have a .NET WinForms app with a WebBrowser control. The WebBrowser control loads a web page that contains an embedded Flash movie. I need to send keystrokes to the Flash movie from the WinForms app. Now MS provides the SendKeys class under the Windows.Forms namespace for this very purpose, but in this instance it doesent pass them on to the Flash movie (Although it does pass them to HTML elements in the page). Hmmmmmm... A little digging in Reflector uncovers the reason. The SendKeys class internally calls the SetKeyboardState() native method to send the keyboard input. Here is what MSDN says about that call:

The SetKeyboardState function copies a 256-byte array of keyboard key states into the calling thread's keyboard input-state table. This is the same table accessed by the GetKeyboardState and GetKeyState functions. Changes made to this table do not affect keyboard input to any other thread.

I'm no expert on how embedded ActiveX controls work within a web page in IE but I bet the Flash control is not running in the same thread as the browser UI. And in the case of using the WebBrowser control, not in the UI thread of the WinForms app. So SendKeys will not be able to send keystrokes to embedded Flash in a WebBrowser control. Just a guess, but it seems that is what is happening here. Well, scratch that, I just checked Spy++ and everything is running under the WinForm UI thread including the Flash ActiveX control. So at this point I have no idea why SendInput() works but SetKeyboardState() doesent (And thus the SendKeys class), very strange indeed! If anyone knows for sure, please leave a comment! :)

So the other option is calling the SendInput method. FYI, this method supersedes the keybd_event method. Here is a sample of the code required to send keystrokes to the foreground window. Remember, you must make sure that the WebBrowser control has focus for it to receive the keystrokes (As does the Flash control in the web page, see further down for more info).

private void Main_Load(object sender, EventArgs e)
{
    WebBrowserControl.Navigate(@"file://C:\Temp\Flash.html");
    Timer.Enabled = true;
}

private int Index = 0;

private void Timer_Tick(object sender, EventArgs e)
{
    Index++;

    NativeMethods.INPUT[] structInput = new NativeMethods.INPUT[1];

    structInput[0] = new NativeMethods.INPUT();
    structInput[0].type = NativeMethods.INPUT_KEYBOARD;
    structInput[0].ki.wScan = 0;
    structInput[0].ki.time = 0;
    structInput[0].ki.dwFlags = 0;
    structInput[0].ki.dwExtraInfo = NativeMethods.GetMessageExtraInfo();
    structInput[0].ki.wVk = NativeMethods.VK_RIGHT;

    // Key up every other pass
    if (Index % 2 == 0)
    {
        structInput[0].ki.dwFlags = NativeMethods.KEYUP;
    }

    NativeMethods.SendInput(1, structInput, Marshal.SizeOf(structInput[0]));
}

The basic native method & struct declarations are as follows. PInvoke.NET has a nice definition of all of these.

The entire project can be downloaded here.