To receive double-click messages, a window must belong to a window class that has the CS_DBLCLKS class style. You set this style when registering the window class, as shown in the following code fragment:
BOOL InitApplication(hInstance)
HANDLE hInstance;
{
WNDCLASS wc;
wc.style = CS_DBLCLKS | CS_HREDRAW | CS_VREDRAW;
wc.lpfnWndProc = (WNDPROC) MainWndProc;
wc.cbClsExtra = 0;
wc.cbWndExtra = 0;
wc.hInstance = hInstance;
wc.hIcon = LoadIcon(NULL, IDI_APPLICATION);
wc.hCursor = LoadCursor(NULL, IDC_IBEAM);
wc.hbrBackground = GetStockObject(WHITE_BRUSH);
wc.lpszMenuName = "MainMenu";
wc.lpszClassName = "MainWClass";
return (RegisterClass(&wc));
}
A double-click message is always preceded by a button-down message. For this reason, applications typically use a double-click message to extend a task that it began during a button-down message.