Why is the owning window showing up above the owned window?

[A D R I A N]

I have this very strange issue. I'm trying to get a window hierarchy to be replicated. So on creating the 1st level dialog, I'm start the instance of the 2nd level dialog.

I've done this in many different ways, but it always shows up as the 2nd level being below the 1st level and then usually a zorder inversion happens (they flip positions). Occasionally, the inversion doesn't happen, but if I click on the owner, the owned immediately jumps to the top of the zorder.

Here are the main parts of a small example to show this happening:

const unsigned short WMA_DIALOGACTION = WM_APP+1;


// Button event handler for the 0th level
void CdialogcallingdialogsDlg::OnBnClickedDlgLvl1()
{
CDlgLvl1 x(this);
x.DoModal();
}


BEGIN_MESSAGE_MAP(CDlgLvl1, CDialogEx)
ON_WM_WINDOWPOSCHANGED()
ON_MESSAGE(WMA_DIALOGACTION, OnDialogAction)
END_MESSAGE_MAP()

void CDlgLvl1::OnWindowPosChanged(WINDOWPOS* lpwndpos)
{
if (!m_shownDlg) {
m_shownDlg = true;
PostMessage(WMA_DIALOGACTION);
}
}

// Level 1 dialog opening up level 2 dialog
LRESULT CDlgLvl1::OnDialogAction(WPARAM wParam, LPARAM lParam)
{
ShowWindow(SW_SHOW);
CDlgLvl2 x(this);
x.DoModal();
return LRESULT();
}


BEGIN_MESSAGE_MAP(CDlgLvl2, CDialogEx)
ON_WM_WINDOWPOSCHANGING()
END_MESSAGE_MAP()

// Level 2 dialog offseting its position
void CDlgLvl2::OnWindowPosChanging(WINDOWPOS* lpwndpos)
{
ASSERT(lpwndpos->hwnd == m_hWnd);
// Offset dialog to see the problem of dlg2 showing up below dlg1
if (!(lpwndpos->flags & SWP_NOMOVE)) {
lpwndpos->x += 10;
lpwndpos->y += 10;
}
}

In the example, you click on the button in the main dialog. That then starts up CDlgLvl1 which then starts up CDlgLvl2. The dialogs are the default dialogs except for the message handling that is shown here and a button on the main application dialog. If you look at it carefully, you can see the inversion.

What am I doing wrong? Perhaps there is a better way to do this?

In case it makes a difference, the issue is more pronounced under Windows 10 and doesn't seem to be visible on Windows 8.1.

A copy of the solution can be pulled from my git repo here:

https://github.com/Ma-XX-oN/dialog-calling-dialogs.git

I've just added some bitmaps on the dialogs to really show the issue, but I've not tested on my 8.1 box yet.

I did a recording of how it pops up and here is frame 0, 2, and 3 of that recording:

Frame 0

Frame 2

Frame 3

As you can see, LVL1 appears over LVL2 in Frame 2, and then flips position in Frame 3.

Full video can be found here.

Using this example project, I've not been able to replicate LVL1 staying overtop of LVL2, but I believe that the behaviour of the zorder inversion not happening is some sort of race condition.

This was originally posted on SO here.


I don't mind someone marking a post as "Proposed as answer", but DO NOT mark it as "Answered". If I am the OP, I will decide if a post actually answers my post or not. Thank you.

Continue reading...