winxpgui.SetLayeredWindowAttributes throwing error pywintypes.error: (87, 'SetLayeredWindowAttributes', 'The parameter is incorrect.')

Question

While I am trying to make a window's background transparent using win32gui, I am using following code.

hwnd = win32gui.FindWindow(None, "My App Name")
win32gui.SetWindowLong (hwnd, win32con.GWL_EXSTYLE, win32gui.GetWindowLong (hwnd, win32con.GWL_EXSTYLE ) | win32con.WS_EX_LAYERED )
winxpgui.SetLayeredWindowAttributes(hwnd, win32api.RGB(0,0,0), 180, win32con.LWA_ALPHA)

But I am getting an error as

pywintypes.error: (87, 'SetLayeredWindowAttributes', 'The parameter is incorrect.')

I tried different documentation, but could not really find anything very specific or helpful. Would anyone like to give some suggestion or code snippet or idea to fix the issue.

Thanks in advance.

Answer 1

Please double check if hwnd is not None. At this answer such code works: Make a window transparent using Win32? All other parameters are constants. Maybe you need FindWindowEx instead of FindWindow. Ex version works across process boundaries, while FindWindow is for this process only.

EDIT1: See this answer: https://stackoverflow.com/a/44276373/3648361 It tells that SetLayeredWindowAttributes() only works on windows that have the WS_EX_LAYERED attribute. But fortunately it can be set by SetWindowLongPtr().