How to access the child window control from another child window

Question

5.00/5 (1 vote)

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I have parent window that has tabControl on it. Then i have made 2 other child window that shown in to that tabControl. In the child1, i have CEdit control and so also in the child2. CEdit in the child2 is a CEdit that show some text from CEdit in the child1 when press enter button in child1. the problem is that whenever i hit the enter button in child1 i get an error. I use this code in enter button :

C#

void child_1::OnBnClickedEnter()
{
    CString CSText;
    m_EnterTextField.GetWindowText(CSText);
    m_View = (CEdit *) GetDlgItem(CE_Child2);//CE_Child2 is the ID from CEdit control in Child2
    m_View->SetWindowText(CSText);//the problem is in here
}

thanks... :)

Posted 1-Sep-13 20:52pm

Hyosoka Poipo

Updated 1-Sep-13 20:54pm

Thanks7872

v2

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Comments

Richard MacCutchan 2-Sep-13 3:11am

What is the error?

Hyosoka Poipo 2-Sep-13 5:10am

the error is ASSERT that something like this:

ASSERT(::IsWindow(m_hWnd));//program stop in this line

Hyosoka Poipo 2-Sep-13 5:13am

i think that the child2 is not created when i wanna set a text in it's CEdit...
but until now i still do not know how to solve this... :-(

Nelek 2-Sep-13 7:03am

You are working with MFC. Are you following the Doc/View structure?

Hyosoka Poipo 2-Sep-13 8:00am

owh... Doc/View Structure....?
i don't understand what you mean Nelek....but i have found the solution that provided by Jochen Arndt....thanks so much... :-)

2 solutions

Solution 2

In one child window, you can only access controls that belong to that window.
The error you're getting is because you're trying to access a control that belongs to another child.

A good way to accomplish what you need would be to send a message from child1 to the parent, so that the parent can then retrieve the edit control value from child1 and set it to child2 using methods in the child windows.

Posted 1-Sep-13 21:18pm

«_Superman_»

Comments

Hyosoka Poipo 2-Sep-13 5:03am

thanks _Superman_,,,em...btw how to send the message from child1 to parent?
i'm not an expert in MFC hehe... :-)

«_Superman_» 2-Sep-13 5:13am

Use GetParent()->SendMessage(WM_XXX);
You would need to define your own custom message like this - #define WM_MYMESSAGE (WM_USER + 1)

Hyosoka Poipo 2-Sep-13 5:38am

waawww... i really don't understand this code, :-(

Hyosoka Poipo 2-Sep-13 5:41am

emmm....may be i have to read win32 programming instead of MFC...but thanks a lot _superman_ :-)

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Jochen Arndt · Accepted Answer · 2013-09-01T21:12:00

Solution 1

The GetDlgItem() function retrieves a pointer to the specified control or child window inside the window for that the function has been called. You are calling this function from the child_1 window with an ID that does not exist in this window and the function will return NULL. To get the pointer to a control in another window, you must call GetDlgItem() for that other window:

m_View = (CEdit *) child_2->GetDlgItem(CE_Child2);

[UPDATE: Detailed solution]

C++

// child1.h
class child_2; // Forward declaration to avoid including child_2.h

class child_1
{
// ...
public:
    void SetChild2(child_2 *p) { m_child2 = p; }
protected:
    child_2 *m_child2;
}

C++

// child1.cpp
#include <child_2.h>

child_1::child_1(void)
{
    m_child_2 = NULL;
}

void child_1::OnBnClickedEnter()
{
    // Check if SetChild2() has been called and the window is valid.
    ASSERT(m_child2 && ::IsWindow(m_child2->m_hWnd));
    m_View = (CEdit *) m_child2->GetDlgItem(CE_Child2);
}

From within OnInitDialog() of the parent dialog of child_1 and child_2 call the SetChild2() function.

Posted 1-Sep-13 21:12pm

Jochen Arndt

Updated 2-Sep-13 0:22am

v2

Comments

Hyosoka Poipo 2-Sep-13 5:01am

Thanks for your answer Jochen Arndt...i have used your suggestion, but when i press enter button,,,there are an error said that "Unhandled exception at 0x50abeb2c(mfc100.dll)......"
then when i hit the break button, VS took me to this :

CWnd* CWnd::GetDlgItem(int nID) const
{
ASSERT(::IsWindow(m_hWnd));//program stop in this line

if (m_pCtrlCont == NULL)
return CWnd::FromHandle(::GetDlgItem(m_hWnd, nID));
else
return m_pCtrlCont->GetDlgItem(nID);
}

Jochen Arndt 2-Sep-13 5:11am

You must off course pass a valid window pointer. It seems that child_2 is invalid here. How did you pass the child_2 pointer to child_1?

If your button handler may be called when child_2 does not exist, you must check this in your code or better use a method like explained by Superman in solution 2.

Hyosoka Poipo 2-Sep-13 5:36am

i made an object of child2 in child1 in the header file
{in child1 header file}
#include "Child_2.h"
..
..
Child2 *chld2;
..
..

then in the cpp file:
void child_1::OnBnClickedEnter()
{
CString CSText;
m_EnterTextField.GetWindowText(CSText);
m_View = (CEdit *) chld2->GetDlgItem(CE_Child2);
m_View->SetWindowText(CSText);
}

did I make an invalid step Jochen ?
thanks... :-)

Jochen Arndt 2-Sep-13 6:13am

Not an invalid step. But you missed the most important one:
Passing the pointer of your existing child_2 window to the member variable of child_1.

I will update by solution.

Hyosoka Poipo 2-Sep-13 6:22am

owh..thanks Jochen Arndt... :-)

Hyosoka Poipo 2-Sep-13 7:48am

amazing....the problem has been solved....
thank you so much Jochen Arndt...
God Bless You... ;-)

Hyosoka Poipo 2-Sep-13 8:23am

owh.. i almost forget,,i have one more question Jochen. It's about this code :
class child_2; // Forward declaration to avoid including child_2.h

the question is why i have to avoid including child_2.h in my child_1 header then just define class child_2....?

thank you again Jochen... :D

Jochen Arndt 2-Sep-13 8:36am

Fine to hear that the problem is solved.

When only using pointers or references to unknown types inside a header file, it is enough to use forward declarations instead of including the header file where the type is defined. However, the header file must be then included in the source file.

It is not really necessary to use the forward declaration in your case. But they must be used when two header files would include each other (e.g. when child_1.h includes child_2.h and child_2.h includes child_1.h).

As a bonus, using forward declarations may reduce the compile time.

Hyosoka Poipo 2-Sep-13 8:58am

oooo... i seee... :-)
btw thanks a looot again Jochen Arndt,,,:-)