C / C++ / MFC

6-May-03 15:17

I have a CDialog derived class CMyDlg. I hope the CMyDlg can release itself automatically. To accomplish this, I implement the CMyDlg:: PostNcDestroy as follows:

CMyDlg::PostNcDestroy()
{
CDialog::PostNcDestroy();
delete this;
}

Then, I always call the following code to create an instance of CMyDlg:

CMyDlg* pMyDlg = new CMyDlg;
pMyDlg->DoModal()

I believe that the PostNcDestroy() function will be called eventually if the CMyDlg is ended from the EndDialog(). And there is no memory leak, since *this* is deleted in the PostNcDestroy().

Can anyone confirm me whether my implementation is OK or not? Rose | [Rose]

Thanks in advance.

lauch

Nish Nishant6-May-03 15:43

6-May-03 15:43

There is nothing wrong in your approach theoretically, but you don't need to do all this. Just create it on the stack and when it goes out of scope it gets destroyed automatically. You only need to create a heap object (which them means you gotta delete it yourself) if you plan on creating a modeless dialog.

Nish

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lauch26-May-03 15:59

6-May-03 15:59

to Nish,
Thanks for your reply. Rose | [Rose]

For some reasons, I must new the CMyDialog as a heap object and it must be a modal dialog box (which is created by the DoModal() function). Therefore, I decide to delete itself in the PostNcDestroy() specifically. I have tested my program, there is no memory leak. However, do you think my appraoch is safe? or is there probably a side effect in this implementaion?

Lauch

Nish Nishant6-May-03 16:07

6-May-03 16:07

lauch2 wrote:
However, do you think my appraoch is safe?

Yup, it's perfectly safe to do this if you insist on doing so.

Nish

lauch26-May-03 20:17

6-May-03 20:17

Nish,
Please help.

After EndDialog() is called, the DoModal() is released. I have walked through the MFC source code of the CDialog::DoModal(), I found DestroyWindow() is called in CDialog::DoModal() function, which in turn call PostNcDestroy() which will delete *this* pointer. And then, the code listed below will also be executed:

PostModal();

// unlock/free resources as necessary
if (m_lpszTemplateName != NULL || m_hDialogTemplate != NULL)
UnlockResource(hDialogTemplate);
if (m_lpszTemplateName != NULL)
FreeResource(hDialogTemplate);

return m_nModalResult;

Since *this* is already freed, all member variable, function method and the memory allocated for the above code is supposed to be freed already, I am not sure whether or not it safe. Any hint?

Thanks.

Nish Nishant7-May-03 3:58

7-May-03 3:58

lauch2 wrote:
I am not sure whether or not it safe.

It's safe, don't worry. When you do your delete you are deleting your dialog object, here they are basically freeing the dialog resource.

Anyway just in case you are still worried, you can move the delete from the PostNCDestroy to just after the DoModal :-

CDlg* a = new CDlg();
a->DoModal();
delete a;

This way you ensure that you delete it only after the call to PostModal from within DoModal.

But seriously I do not think there is any problem right now.

Regards,
Nish

Nish Nishant7-May-03 4:01

7-May-03 4:01

On second thoughts I suggest that you do this :-

CDlg* a = new CDlg();
a->DoModal();
delete a;

Because if PostModal gets called after you delete the object then it is actually trying to access members of an object that does not exist anymore. This might cause problems as you can guess.

Nish

lauch28-May-03 16:37

How to copy from clipboard to MS Word Project???

8-May-03 16:37

Nish,

Another question:

Do you know any messages will send to a dialog subsequently after calling the EndDialog() to triggle the dailog to close itself?

lauch

krle6-May-03 15:08

krle

6-May-03 15:08

If anybody knows how to implement automation function in Visual C++ to copy bitmap that resides on the clipboard to a MS Word documetn. Sounds so simple but I am clueless. Please HELP!!!

Why won't my CTreeCtrl work in my SDI

adonisv6-May-03 11:43

6-May-03 11:43

I have a single document interface application. Its base class is CFormView. I've added a CTreeCtrl to it just like I would in a dialog based application. I've given the tree control an Id and I've created a variable of type CTreeCtrl. However, when I try to use it my application crashes. Its seems that my tree control has not been initialized... Cry | :((

this->m_ctrlSetupTree {CTreeCtrl hWnd=0x00000000} Dead | X|

valikac6-May-03 12:46

valikac

6-May-03 12:46

The the code that creates the CTreeCtrl object, i.e. Create().

Kuphryn

adonisv6-May-03 13:35

6-May-03 13:35

How do I get the parent CWnd* pParentWnd? OMG | :OMG:

BOOL Create( DWORD dwStyle, const RECT& rect, CWnd* pParentWnd, UINT nID );

valikac6-May-03 16:16

valikac

6-May-03 16:16

Call GetParent().

Kuphryn

Tibor Blazko6-May-03 23:57

Tibor Blazko

6-May-03 23:57

isn't it your view? this (or similar)
t!

Michael Dunn6-May-03 17:27

Michael Dunn

6-May-03 17:27

Are you calling InitCommonControls()?

--Mike--
Eh! Steve!
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Chris Richardson6-May-03 18:21

6-May-03 18:21

I would bet you are trying to use it before the tree control has been created. Are you trying to access the tree control in a WM_SIZE handler? If so, it won't be created the first couple times the WM_SIZE handler gets called. Usually, the fix for this is something like this:

if( !IsWindow( m_YourTreeCtrl ) )
   return;

// Here, m_YourTreeCtrl can be accessed safely.

However, if you are trying to access the tree in a function that's only called once (say, for initialization), then you'll have to put the initialization code in some other function that's called later on.

Chris Richardson
Terrain Software

adonisv7-May-03 10:23

7-May-03 10:23

I'm calling the following code. But it seems that my hWnd is still null.

CRect treeRect;
treeRect.NormalizeRect();
CImageList *pImageList=new CImageList;
	
	
if(this->m_ctrlSetupTree.Create(WS_VISIBLE,treeRect,this,IDC_SETUP_TREE))
	{
		Beep(999,99);
		int i, icons=0;
		for (icons=0; RCanalTree::m_icons[icons]; icons++) {}
		pImageList->Create(16, 16, TRUE, icons,6);
		for (i=0; RCanalTree::m_icons[i]; i++)
		{
			pImageList->Add(AfxGetApp()->LoadIcon(RCanalTree::m_icons[i]));
		}
		// Assign the image list to all list and tree controls
		// so that icons can be used.	
		m_ctrlSetupTree.SetImageList(pImageList,TVSIL_NORMAL);
		
		// Instruct the Canal Manager to create a new system based on the information
		// in the Canal Structures database.
		
		
		if(this->m_oCanalManager.CreateNewDataStructures())
		{
			// Based on the data structures created in memory by the Canal Manager,
			// populate the setup tree.
			//this->m_ctrlSetupTree.Populate();
		}
		
	}
}

Chris Richardson7-May-03 10:33

7-May-03 10:33

Your control is failing to be created because you haven't specified the WS_CHILD style. Here's the correct line of code:

if(this->m_ctrlSetupTree.Create(WS_CHILD|WS_VISIBLE,treeRect,this,IDC_SETUP_TREE))
{
   ..... snip .....
}

Chris Richardson
Terrain Software

adonisv7-May-03 11:11

7-May-03 11:11

Hmmmm...Create still returned zero.. Frown | :(

CTreeCtrl::Create returned 0

if(this->m_ctrlSetupTree.Create(WS_CHILD|WS_VISIBLE|TVS_HASLINES,treeRect,this,IDC_SETUP_TREE))

Chris Richardson7-May-03 11:16

7-May-03 11:16

Has the window referred to by "this" been created at the point you are calling Create? That's my only guess as to why it would still be failing.

Chris Richardson
Terrain Software

adonisv8-May-03 14:42

8-May-03 14:42

Hmmm.... good point. Cool | :cool:

Exactly when in the "window" created in an SDI application with formView as the base class??? Laugh | :laugh:

Chris Richardson8-May-03 15:52