Send message from dialog to child

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I found in internet a method to send messages from child to dialog, but if I want to send message from dialog to child?

What I have tried:

To send from child to dialog I founf this method:

#define UWM_CUSTOM (WM_APP+1)

// in child
CString str = _T("Test");
GetParent()->SendMessage(UWM_CUSTOM, (WPARAM)&str, 0);

// in parent
ON_MESSAGE(UWM_CUSTOM, OnCustom)

LRESULT Cxx::OnCustom(WPARAM wparam, LPARAM lparam)
{ CString* pstr = (CString*)wparam;
  ...use pstr
  return 0;
}

but I want to do the opposite

Posted 3-Oct-19 20:28pm

Member 14594285

Updated 3-Oct-19 23:00pm

Leo Chapiro

v2

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Comments

Mohibur Rashid 4-Oct-19 2:43am

If you know the CWnd pointer you definitely can write something like this
child_window->SendMessage(...);

You will have to store the child_window address in some sort of variable, Other wise you will have to find another method to identify your child.

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Leo Chapiro · Answer 1 · 2019-10-03T23:01:00

Solution 1

If your child window is modeless, you can use the pointer to your dialog and use

C++

#define UWM_CUSTOM (WM_APP+1)

// in parent
void CMFCApplicationTestDlg::OnBnClickedButCreatedlg()
{
	CString str = _T("Test");
	CChildDlg* pChildDlg = new CChildDlg(this);
	pChildDlg->Create(IDD_DIALOG_CHILD, this);

	pChildDlg->ShowWindow(SW_SHOW);

       //pChildDlg->SendMessage(UWM_CUSTOM, (WPARAM)&str, 0);
       // Better
       pChildDlg->PostMessage(UWM_CUSTOM, (WPARAM)&str, 0);
}

If your child window is modal, you can't because after

C++

DoModal()

returns, the dialog will already be destroyed.

Posted 3-Oct-19 23:01pm

Leo Chapiro

Updated 4-Oct-19 1:26am

v6

Comments

Member 14594285 4-Oct-19 5:31am

what is pChildDlg?

Member 14594285 4-Oct-19 5:34am

anyway I used ShowWindow(true) to show child dialog

KarstenK 4-Oct-19 5:36am

pChildDlg is the pointer to the child dialog. You better use PostMessage to not block the internal message queue which may result in a blocking app.

Member 14594285 4-Oct-19 5:41am

so I must write.
MyDlg * pChildDlg = new pChildDlg;

pChildDlg->SendMessage(UWM_CUSTOM, (WPARAM)&str, 0);

Leo Chapiro 4-Oct-19 5:43am

Yes, better as Karsten mentioned, you use the PostMessage.

Member 14594285 4-Oct-19 5:59am

I tried but it doesn't work, my parent dialog has a button that when is clicked opens child dialog, I tried like you've wrote but it doesn't work

Member 14594285 4-Oct-19 6:01am

I wrote:
MyDlg2 * pChild = new MyDlg2;

pChild->SendMessage(UWM_CUSTOM, (WPARAM)&stra, 0);

but when I do debug there is an error

Leo Chapiro 4-Oct-19 7:25am

I have updated, take a look (above).

Member 14594285 4-Oct-19 8:26am

It doesn't work
I wrote in parent dialog:

CString str = _T("Test");
MyDlg2* pChildDlg = new MyDlg2(this);
pChildDlg->Create(IDCANCEL, this);

pChildDlg->ShowWindow(SW_SHOW);

//pChildDlg->SendMessage(UWM_CUSTOM, (WPARAM)&str, 0);
// Better
pChildDlg->PostMessage(UWM_CUSTOM, (WPARAM)&str, 0);
//dlg.DoModal();// TODO: Add your control notification handler code here

in child dialog:

BEGIN_MESSAGE_MAP(MyDlg2, CDialogEx)
ON_BN_CLICKED(IDC_BUTT_DIALOG, &MyDlg2::OnBnClickedButtDialog)
ON_MESSAGE(UWM_CUSTOM, OnCustoma)
END_MESSAGE_MAP()

and:
LRESULT MyDlg2::OnCustoma(WPARAM wparam, LPARAM lparam)
{
CString* pstr = (CString*)wparam;

//testo.SetWindowText(*pstr);
m_text.SetWindowText(*pstr);

return 0;
}

but it doesn't work

Leo Chapiro 4-Oct-19 8:38am

It can not work: pChildDlg->Create(IDCANCEL, this);
You need to create a new dialog first, the IDD_DIALOG_CHILD in my example is its ID. Take a look: Create a Modeless Dialog Box as Child Window

Member 14594285 4-Oct-19 8:45am

I have already my dialog, it's static, id of my child dialog is IDCANCEL