PostNcDestroy problems

andyg 101

Hi there, I am having trouble with my dialogues using the cross X in the corner of my dialogue doesn't seem to call PostNcDestroy where I perform clean up of the object. I was expecting the WM_CLOSE message to be generated which calls the default DestroyWindow. Can anyone explain why it is not being called? Andy

David Crow

Interesting. I have a modeless dialog I use in a little app that simply shows a progress bar while the app is running. When I click the 'X', it indeed calls the dialog's PostNcDestroy() function.

John M Drescher

I don't think it is called in modal dialogs. John

andyg 101

I don't understand it, I stepped through some of the example code in Nishants tutorial and closing the dialogue with the X definitely calls PostNcDestroy, however it doesn't in mine, despite the fact that clicking the X sends the WM_CLOSE message, which I think should call destroy window. I'm confused, the only difference I can see in my code is that I call ShowWindow in the constructor of my dialogue, and not in the external code. ?? Andy :-( Still confused

John M Drescher

Is your dialog modeless then? John

andyg 101

It's definetly modeless, I create a new dialogue like this

if(!m_pDlgComms) // check to see if the dialogue exists
{
m_pDlgComms = new CCommsDlg(this);

etc which is then constructed like this

CCommsDlg::CCommsDlg(CWnd* pParent /*=NULL*/)
: CDialog(CCommsDlg::IDD, pParent)
{
//{{AFX_DATA_INIT(CCommsDlg)
m_sCommsInput = _T("");
m_sCommsOutput = _T("");
//}}AFX_DATA_INIT
if (Create(CCommsDlg::IDD, pParent))
{
m_pParent = pParent;
ShowWindow(SW_SHOW);
}
}

and here is the PostNcDestroy which is called whenever I force a destroy window using a button for example

void CCommsDlg::PostNcDestroy()
{
// TODO: Add your specialized code here and/or call the base class
CDialog::PostNcDestroy();
if(m_pParent)
{

	((CBuggycontrolappView\*)m\_pParent)->m\_pDlgComms			= NULL;
	((CBuggycontrolappView\*)m\_pParent)->m\_nCommsToggleState = 0;
}
delete this;

}

but not when I use the cross. Even though there is a WM_CLOSE message Andy

John M Drescher

Ok, I understand your problem but I have not seen this in the past. Do you have code for OnCancel() ? Destroying the window with the X button should call OnCancel(). John

Toni78

When WM_CLOSE is sent, you need to send call DestroyWindow() For example:

CCommsDlg::OnClose()
{
DestroyWindow();
}

This is how you close a modeless dialog. When you call DestroyWindow() then of course you will get to PostNcDestroy(). // Afterall I realized that even my comment lines have bugs

andyg 101

Hello again guys I've solved the problem I think. I put in the handler for WM_CLOSE, and the following code

void CCommsDlg::OnClose()
{
CDialog::OnClose();

DestroyWindow();

}

This now works fine, doing exactly what I want. Previously the code I had used was

void CCommsDlg::OnClose()
{
DestroyWindow();

CDialog::OnClose();

}

which gave me the exception. I'm still not sure why though no doubt one of you guys can inform me and I'm still puzzled by the fact that the code given in Nishants example in the dialogues section makes no call to OnClose at all and still calls PostNcDestroy. However now my code works I'm a happy man :-) though it'd be better if I understood why! Cheers Andy

Toni78

As Nishant explains in his article a modal dialog makes a call to DestroyWindow() and as a result to PostNcDestroy(). But in your example you are building a modeless dialog and Windows is very specific about this case. You need to call DestroyWindow() to close a modeless dialog. Why? I don't know. This decision was made by windows. I will do a little bit of investigating though to find out. However, in this case OnClose() doesn't generate an WM_DESTROY message afterwards. And by the way this part of your code DestroyWindow(); CDialog::OnClose(); generates an exception because you are sending a WM_CLOSE message to a window that doesn't exist. // Afterall I realized that even my comment lines have bugs