When is a window visible yet not visible?

Raymond Chen

Raymond

Today, a quick puzzler.

Consider the following code fragment:

 ShowWindow(hwnd, SW_SHOWNORMAL);
 assert(IsWindowVisible(hwnd));

We just showed the window, certainly it is visible, right?
Yet the assertion can fire (even in the absence of multi-threading). Why?

Answer below – stop reading if you want to try to solve it yourself.

Take a look at

the IsWindowVisible function
.

If the specified window, its parent window, its parent’s parent window,
and so forth, have the WS_VISIBLE style,
the return value is nonzero. Otherwise, the return value is zero.

The WS_VISIBLE style indicates that this window is
visible in its parent. But the parent itself might not be visible,
in which case IsWindowVisible returns FALSE.

[Raymond is currently on vacation; this message was pre-recorded.]

Raymond Chen
Raymond Chen

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