GWL_USERDATA

When you send a WM_CLOSE message to a window, it tries to close the window as if the X button were pressed.You cannot know whether the application was closed externally or by clicking the X button

But there is an easy alternative. When you are closing the window externally using WM_CLOSE, you can initialize its 32-bit user data value using the SetWindowLong function before sending the message. In the target application (being closed) you will query this user data using GetWindowLong function and execute your code accordingly.

The user data value is set to 0 by default. You can set it to any non-zero value before sending the WM_CLOSE 

.message

Set the user data value of the target window to -1'

(originally 0)'

WIN32'

SetWindowLong CurrApp,GWL_USERDATA,-1

send closing messgae'

CurrApp is a Handle to the window

&SendMessage CurrApp,WM_CLOSE, 0,ByVal 0

Private Sub Form_QueryUnload(Cancel As Integer, UnloadMode As Integer)

    If GetWindowLong(hwnd, GWL_USERDATA) = 0 Then

        MsgBox "Closing from X."

    Else '(if -1)

        MsgBox "Closing externally using WM_CLOSE."

    End If

End Sub

بستن پنجره ( API )

WM_CLOSE=&H10

&SendMessageA hwnd,WM_CLOSE,0,0