Question

I want to focus a windows when it is blinking/flashing. The more common case is when someone sends some text by a chat software (for example MSN). In this case the windows bar is going to start blink in the start bar. I don’t know if i am explaining myself. I want to get the HWND of the blinking windows. If more info is necesary to understand it, I will try to explain me better.

I have already searched info about this case but I find nothing. Maybe it can be resolver using “win32gui” library.

Thank you for your help!!!

Answer 1

First, most programs flash their windows by calling FlashWindowEx (or some higher-level function that wraps it). But there are a few apps—mostly from Microsoft—that do some custom stuff instead that looks like window-flashing to the end user, but may not look the same under the covers. Hopefully, you don’t care about any such custom apps.

Anyway, the easiest way to capture that information is to install a shell hook with SetWindowsHookEx or RegisterShellHookWindow. (You could instead explicitly inject code in front of user32.dll… but you don’t want to try that from Python.) When you do this, Windows will treat your window as if it were part of Explorer (the “shell”) and send it special messages about what other programs are doing—in particular, WM_SHELLHOOKMESSAGE.

As forivall pointed out, this might be easier to do from AutoHotkey—this answer in the forums shows how to do it. It might also be easier to do from VB, or even C++. Yes, those languages are generally more difficult than Python, but the actual logic in your code is pretty trivial, and the only hard part is getting the shell hook messages, and that part will be easier in those languages. Another alternative is to use IronPython and do it via .NET.

But you asked if it’s possible to do it from Python, and… yes, it is. I believe the relevant functions are not wrapped up by win32gui, so you’ll have to use ctypes to do it from Python. See this SO question for a possible example, and look at some of the Related questions on the side and the ctypes docs for other examples of using ctypes to call different functions out of user.dll.

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If you want to set a windows hook, the key function will look something like this (see ShellProc for details):

HSHELL_REDRAW=6
WM_SHELL=10

def my_callback(nCode, wParam, lParam):
    if nCode == HSHELL_REDRAW and lParam:
        got_flashing_window_with_hwnd(wParam)

hook = user32.SetWindowsHookEx(WM_SHELL, my_callback, None, 0)

But you need to set the types and push the callback through ctypes.

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If you already have a window that you’re managing from Python, it’s probably easier to set yourself up as a shell hook window instead:

user32.RegisterShellHookWindow(my_hwnd)

Then, in your window proc:

WM_SHELLHOOKMESSAGE = None
def wndproc(hWnd, uMsg, lParam, wParam):
    if WM_SHELLHOOKMESSAGE is None:
        WM_SHELLHOOKMESSAGE = user32.RegisterWindowMessage('SHELLHOOK')
    if uMsg == WM_SHELLHOOKMESSAGE and wParam == HSHELL_FLASH:
        got_flashing_window_with_hwnd(lParam)

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I’m not sure whether you need elevated privileges for either of these, but I would suspect you do.