Problem with accessing controls in Dialog

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Hi everyone,

Sorry for the repost of a question yesterday, I dint find the 'reply' link in my page, so only i went for that option.

Kindly glarify my doubt.I have a dialog class(CSampleDlg), in that I drag and drop, a ListControl(m_gridOutput) and a edit control. And I've added one class(CDerivedOne) derived from CSampleDlg.

In listcontrol, i have CheckBox items. Now i am trying to Check/Uncheck the Listcontrol item from Derived class through function call, like this.

m_gridOutput.SetCheck(Id,TRUE);

But i am getting assertion error at this point. The assertion error comes at the follwing line(in SetCheck function),

ASSERT(::IsWindow(m_hWnd));

Similarly if i try to access any control in my Dialog from derived class, the result will be the same.But there is no assertion, if i try to access within my dialog class.

What should i do, to access the controls in my dialog from any class, What i am missing here?

Any help is greatly appreciated.

Shiva.

Posted 7-Apr-11 18:32pm

Shiva S.S

Updated 7-Apr-11 18:38pm

JF2015

v2

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Comments

Olivier Levrey 8-Apr-11 6:09am

You should write your comment under Eugen's answer, otherwise, he will never be notified. I did it for you.

3 solutions

Solution 3

Where are you calling m_gridOutput.SetCheck(Id,TRUE) from? If I had to guess what's happening, you're trying to do this at some point when the window hasn't been created. If you have a CDialog derived class, all GUI initialization should take place on the OnInitDialog() call and NOT the contructor. By the same token, when accessing these variables from a class who owns the CDialog, the window still has to be created before any of them can be accessed.

Those controls are typically private members, not allowing you to access them from a derived class or any other class other than the actual owner, this is meant to keep you from accessing those controls when the window doesn't exist, as is your case. If you REALLY know what you're doing, you can make them protected to access from derived classes or public to access from anywhere, but I'd only recommend that if you know MFC well enough.

Posted 8-Apr-11 10:13am

Albert Holguin

Comments

Shiva S.S 9-Apr-11 1:39am

Hi Albert,
Thanks a lot for your answer.So if i want to access any control(of CDialog)from my derived class ,before i need to create the window, here what is meant by creating the window?.

And ofcourse, i am doing all my GUI initialization in OnInitDialog(), not the constructor. Should i reinitilaize all my GUI controls in my derived class, if i want to access it from Derived one?.

Please glarify this, it will be very much helpful for me.And i already googled related to this, if you can please provide any articles related to this.

Shiva.

Albert Holguin 9-Apr-11 14:07pm

Let me look for a good article on the subject for you... what is meant by creating the window, is actually creating the window itself, not constructing the object (i.e. calling CreateWindow() versus constructor CDialog())... as for your other question, if you've initialized controls in your base class, you don't have to reinitialize, you just have to call that method first (call CBaseDialog::OnInitDialog() as your first call within CDerivedDialog()::OnInitDialog)... your problem with this control is trivial and the cause can probably be easily spotted if you post more of your code.

Albert Holguin 10-Apr-11 15:19pm

I can't really find a really good article on this, but MSDN provides a somewhat detailed explanation on the process of creating CDialog objects:
http://msdn.microsoft.com/en-us/library/132s802t.aspx

Shiva S.S 11-Apr-11 2:44am

Thanks for your reply Albert. i shall post part of my code, please go through.
In Base.h file,
class CBaseDialogDlg : public CDialog
{
public:
CSampleDialogLogicDlg(CWnd* pParent = NULL); // standard constructor
virtual BOOL OnInitDialog();
protected:
virtual void DoDataExchange(CDataExchange* pDX); // DDX/DDV support
/****Some Variable declaration********/
};
In my Base.cpp file,
CBaseDialogDlg::CBaseDialogDlg(CWnd* pParent /*=NULL*/)
: CDialog(CBaseDialogDlg::IDD, pParent)
{
m_hIcon = AfxGetApp()->LoadIcon(IDR_MAINFRAME);
}
void CBaseDialogDlg::DoDataExchange(CDataExchange* pDX)
{
CDialog::DoDataExchange(pDX);
DDX_Control(pDX, IDC_LIST2, m_gridCtrlEx); // List control
DDX_Control(pDX, IDC_EDIT1, t_findVar);
DDX_Control(pDX, IDC_LIST1, m_gridOutput); // List control2
DDX_Control(pDX, IDC_BUTTON1, b_startThread);
}
BOOL CBaseDialogDlg::OnInitDialog()
{
CDialog::OnInitDialog();
// Some auto code

//Inserting items into list control
m_gridOutput.SetExtendedStyle(m_gridCtrlEx.GetExtendedStyle() | LVS_EX_CHECKBOXES);

m_gridOutput.SendMessage(LVM_SETEXTENDEDLISTVIEWSTYLE | LVS_LIST | LVS_EX_CHECKBOXES | DFCS_CHECKED,0,0);

for(int index = 0; index <(sizeof(Nv_OutputBits) / sizeof(int));index++)
{
m_gridOutput.InsertItem(index,Nv_OutputBits[index]);
}
ChangeCheckStatus(1); // NO PROBLEM WITH THIS CALL
}
void CBaseDialogDlg::ChangeCheckStatus(int VarId)
{
m_gridOutput.SetCheck(VarId,TRUE);
}

In my derived .h file,
class CMlkOne : public CBaseDialogDlg
{
public:
CMlkOne();
//Some code
virtual BOOL OnInitDialog();
protected:
virtual void DoDataExchange(CDataExchange* pDX);
};

In my derived cpp file,

CMlkOne::CMlkOne()
{

}
BOOL CMlkOne::OnInitDialog()
{
return TRUE;
}
void CMlkOne::DoDataExchange(CDataExchange* pDX)
{
CSampleDialogLogicDlg::DoDataExchange(pDX);
}
void CMlkOne::ChangeVariableValue(int VarId, int VarValue)
{
CSampleDialogLogicDlg objBaseDialog;
objBaseDialog.ChangeCheckStatus(2); // Assertion Error bcos of this line
}

Should i add some extra initialization code in DoDataExchange(Derived) or OnInitDialog(Derived)?, what i am missing in my derived class, i am struggling with this, Any help will be very much helpful.

Shiva.

Olivier Levrey 11-Apr-11 4:01am

OK I got your mistake. See my updated answer. Albert, have a 5 for your good explanations.

Espen Harlinn 10-Apr-11 15:13pm

Nice effort, my 5

Albert Holguin 10-Apr-11 15:13pm

thanks espen :)

Solution 1

Please post the code of the void CDerivedOne::DoDataExchange(CDataExchange* pDX) function here :)

Posted 7-Apr-11 21:50pm

Eugen Podsypalnikov

Comments

Olivier Levrey 8-Apr-11 6:08am

Op commented: Thank you so much Eugen. I cannot find, DoDataExchange in my derived class. Should i include it,by using properties window(or) it will be auto generated?. Pls reply.

Eugen Podsypalnikov 8-Apr-11 6:43am

You could try to implement your derived function :) :
void CDerivedOne::DoDataExchange(CDataExchange* pDX)
{
CSampleDlg::DoDataExchange(pDX);
}

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Olivier Levrey · Accepted Answer · 2011-04-07T22:44:00

Solution 2

If ASSERT(::IsWindow(m_hWnd)) failed, it means that the dialog (or the control) you are trying to access was not created yet.

It is often tricky to make a class inherit from an existing CDialog one. I would like to ask several questions:
- Is CSampleDlg a fully functionnal dialog? I mean can you display it using DoModal without problem?
- Why does CDerivedOne inherit from CSampleDlg?
--> do you use a different resource for CDerivedOne?
--> or is this class just to add some methods and members to CSampleDlg without modifying the UI?

Could you post the .h files and the .cpp files (at least the constructors, DoDataExchange, OnInitDialog, and macros like BEGIN_MESSAGE_MAP, DECLARE_DYNAMIC, ...)

----------------

I read your code from your comments and the problem is easy to fix:

void CMlkOne::ChangeVariableValue(int VarId, int VarValue)
{
    CSampleDialogLogicDlg objBaseDialog;
    objBaseDialog.ChangeCheckStatus(2); // Assertion Error bcos of this line
}

You have an asssertion here because even though you instanciated the dialog object,
the dialog resource is not created yet (it is created after DoModal is called for example).
Moreover, what you want here is not instanciating another object, but calling the base method.
So just replace your code by this one:

void CMlkOne::ChangeVariableValue(int VarId, int VarValue)
{
    //call the base class method
    CSampleDialogLogicDlg::ChangeCheckStatus(2);
}

-----------------------

Shiva, I just saw an error I hadn't seen before: you overrided OnInitDialog in CMlkOne class like this:

BOOL CMlkOne::OnInitDialog()
{
    return TRUE;
}

This can't work. All initialization is done in OnInitDialog and with your code, you just by-pass the initialization so your dialog is not created!
You must call the base method:

BOOL CMlkOne::OnInitDialog()
{
    return __super::OnInitDialog();
}

And if you want to call ChangeVariableValue in OnInitDialog, do like this:

BOOL CMlkOne::OnInitDialog()
{
    //initialize the dialog first
    __super::OnInitDialog();
    //now you can call this because all your controls are initialized
    ChangeVariableValue(2);
    return TRUE;
}

I hope it is clear this time.

Posted 7-Apr-11 22:44pm

Olivier Levrey

Updated 11-Apr-11 2:32am

v3

Comments

Albert Holguin 8-Apr-11 16:15pm

see my answer and tell me what you think... i see this error commonly when people start to get too smart with MFC before they really know how it works.

Hyosoka Poipo 29-Aug-13 0:00am

i have the same problem...
i'm using tabcontrol and have some child window....

the question is,,how do I access the child window control from other child window..?

i have read all of this conversation, but still didn't find a solution

thanks..

Shiva S.S 9-Apr-11 1:26am

Thanks a lot Olivier, for your reply. Here I am answering your questions.
->Yes,CSampleDlg is fully functional one.I can display it, using DoModal.
->I am not using different resource for CDerivedOne,as you said it is just to add some methods.
Pls reply.

Olivier Levrey 30-Aug-13 18:57pm

You should post your question in the Question section instead of adding a comment. If you post some code and give me the link to your question, I'll have a look at it.

Shiva S.S 11-Apr-11 6:46am

Hi Olivier,
Thanks for your quick reply,the idea you gave me was very much helpful, i tried to replace that line, with your code. But it gives the following compile time error.

CSampleDialogLogicDlg::ChangeCheckStatus(2); //Compilation error at this line

error:'CSampleDialogLogicDlg::ChangeCheckStatus' : illegal call of non static member function.

What should i do to rectify this? Please reply.
Shiva.

Hyosoka Poipo 2-Sep-13 2:53am

thanks Oliver, :-)
i have put my question in this link :
http://www.codeproject.com/Questions/646658/How-to-access-the-child-window-control-from-anothe

Olivier Levrey 11-Apr-11 7:20am

Isn't CMlkOne derived from CSampleDialogLogicDlg? It should compile. You may also try with __super::... instead of CSampleDialogLogicDlg::....

Shiva S.S 11-Apr-11 8:12am

Hi Olivier,

I found the probelm and cleared it. It is running, but sorry to say, it is giving Assertion error again at the same line.i tried with all the possibilities(SetCheck,SetCheckState,SetItemState). How can i fix it?,Please reply me.

Shiva.

Olivier Levrey 11-Apr-11 8:32am

I updated my answer.

Albert Holguin 11-Apr-11 9:29am

great catches and follow up oliver!

Albert Holguin 11-Apr-11 9:30am

I knew it'd be easy to catch if he posted code

Olivier Levrey 11-Apr-11 9:34am

Yes. Posting relevant code should be automatic. Helping/debugging is so easier when you see the code...
Thank you Albert.

Shiva S.S 11-Apr-11 9:33am

Hi olivier,

Now i want to glarify one thing here, i tried this line in my derived OnInitDialog(),

return __super::OnInitDialog();
but it is giving assertion error(ASSERT(::IsWindow(m_hWnd))continuously, My doubt is , how this OnInitDialog() should be called, in my derived class?
Will it be called automatically like in CBaseDialog Class, or i should call?, I know that OnInitDialog will be called when 'DoModal' the dialog.
If i should 'DoModal', how it should be done, which will be the best place to do?. if this is clear, it will be much helpful for me. Please reply.
Shiva..

Olivier Levrey 11-Apr-11 9:43am

OnInitDialog is called automatically by the framework when the dialog is first displayed. After a DoModal, or Create (for model-less dialogs).

- You should not call OnInitDialog from your code, unless you override it.
- If you override it, the first line should be:
__super::OnInitDialog();
- After that line, your controls are initialized.
- After that, you must not call OnInitDialog again.

Shiva S.S 11-Apr-11 9:50am

Thanks Olivier,
Here i am not calling OnInitDialog() anywhere in my code, but if i put a breakpoint in my derived OnInitDialog and see, control never comes inside, when will be this derived OnInitDialog get called?.
Shiva..

Olivier Levrey 11-Apr-11 9:53am

It is called after you call DoModal or Create.

Shiva S.S 30-Apr-11 2:52am

Hi everyone,

After a bit struggle, finally i found where i went wrong.I thank everyone, who helped me in this,Special thanks to Olivier, who spent lot of time for me,i learned a lot from his answers.

Now i am able to access my controls in my Base dialog, from any of my derived class.

Problem was with this line,CBaseDialogLogicDlg objBaseDialog;

objBaseDialog.ChangeCheckStatus(2);

Here i am creating an object of my base class,and simply calling my base class member function, which updates the control.

I made two correctionsin my derived class.

1.Instead of a normal object, i've created a pointer object to my base class.

CBaseDialogLogicDlg *objBaseDialog;

2.Then i need to add the following lines in my derived class, before using my pointer object.

LPVOID lpParam;objBaseDialog = (CBaseDialogLogicDlg *)lpParam;

This lpParam is 'this' pointer of my CBaseDialogLogicDlg dialog class.

Now i can access any of my control of my base dialog from my derived class itself.

Hope i fixed the problem correctly.

Olivier Levrey 2-May-11 3:37am

Good. I am glad you could fix your problem.