Is there a way to detect if a Window has been flashed? - windows

Question

Using functions FlashWindow and FlashWindowEx, one can cause a window to flash. However, I can't seem to find any API that would detect if a window has been flashed. Does one exist?
Edit
Given that FLASHWINFO has DWORD dwFlags, I would have guessed that this info would be stored in the window and would be accessible using either GetWindowLongW or GetWindowLongPtrW, but I can't find it there.
Reason I need this is for automation.

Answer 1

According to the ShellProc:
lParam [in]
Type: LPARAM
HSHELL_REDRAW The value is TRUE if the window is flashing, or FALSE otherwise.
So we just need to add a SetWindowsHookExA function to catch the WH_SHELL message.
Here is a sample:
#include <Windows.h>
LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);
LRESULT CALLBACK procShell(int, WPARAM, LPARAM);
int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, PSTR szCmdLine, int iCmdShow)
{
HHOOK hook = SetWindowsHookEx(WH_SHELL, procShell, NULL,GetCurrentThreadId());
int e = GetLastError();
static TCHAR szAppName[] = TEXT("Test Flashing");
HWND hwnd;
MSG msg;
WNDCLASS wndclass;
wndclass.style = CS_HREDRAW | CS_VREDRAW;
wndclass.lpfnWndProc = WndProc;
wndclass.cbClsExtra = 0;
wndclass.cbWndExtra = 0;
wndclass.hInstance = hInstance;
wndclass.hIcon = LoadIcon(NULL, IDI_APPLICATION);
wndclass.hCursor = LoadCursor(NULL, IDC_ARROW);
wndclass.hbrBackground = (HBRUSH)GetStockObject(WHITE_BRUSH);
wndclass.lpszMenuName = NULL;
wndclass.lpszClassName = szAppName;
if (!RegisterClass(&wndclass))
{
MessageBox(NULL, TEXT("This program requires Windows NT!"), szAppName, MB_ICONERROR);
}
hwnd = CreateWindow(szAppName,
szAppName,
WS_OVERLAPPEDWINDOW,
CW_USEDEFAULT,
CW_USEDEFAULT,
CW_USEDEFAULT,
CW_USEDEFAULT,
NULL,
NULL,
hInstance,
NULL);
ShowWindow(hwnd, iCmdShow);
UpdateWindow(hwnd);
while (GetMessageW(&msg, NULL, 0, 0))
{
TranslateMessage(&msg);
DispatchMessageW(&msg);
}
UnhookWindowsHookEx(hook);
return msg.wParam;
}
LRESULT CALLBACK WndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
switch (message)
{
case WM_DESTROY:
PostQuitMessage(0);
return 0;
case WM_LBUTTONDOWN:
FlashWindow(hwnd, TRUE);
return 0;
}
return DefWindowProc(hwnd, message, wParam, lParam);
}
LRESULT CALLBACK procShell(int nCode, WPARAM wParam, LPARAM lParam) {
if (nCode == HSHELL_REDRAW) {
if (lParam)
{
OutputDebugString(L"Window is flashing\n");
}
}
return CallNextHookEx(NULL, nCode, wParam, lParam);
}
If we press the left button, the FlashWindow will be called. Then the hook function will get the HSHELL_REDRAW message and output: