I looked for many code. All of them says of replacing "CDialog" class with user defined class. But the problem is, I have many other functions and member variable definition in Dialog that I can't omit, otherwise my application window functionality will be gone.
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I am working on a Windows application using MFC and Visual Studio C++ 17.
I have multiple tabs in the application, one of which is currently implemented using CListBox and needs to be reimplemented using CCheckListBox.
CCheckListBox is a child class of CListBox.
I have a vector of unique CString's I want to display in the box.
To start simple, I tried making the tab with CListBox and by using CListBox::AddString(), this worked exactly as I wanted it to. It sorted the strings alphabetically, and automatically added a scroll bar on the side when the vector had too many CString's to display all at once in the list.
However, when swapping the CListBox variable to a CCheckListBox variable, I have come across the error when I press run along the lines of:
Debug Assertion Failed! ..... \mfc\winctrl3.cpp Line: 588
I found this GitHub link that has the winctrl3.cpp file and on line 588, there is a function called OnLButtonDblClk which is somewhat explained here.
The trouble is I am unsure of how to swap a variable from a parent class to a child class. Is it so different for Windows classes? In the courses and programs I have taken and written in the past, switching from a parent to child variable was straightforward but this is quite the opposite !
Any help is appreciated, thank you in advance ! :D
There is no assertion in line 588 of the source file in your link. That github upload dates back to 2014. Why not search the winctrl3.cpp source file in your own Visual Studio installation instead? In my own installation, it is in function PreSubclassWindow() and there is indeed an assertion there:
// CCheckListBoxes must be owner drawn
ASSERT(GetStyle() & (LBS_OWNERDRAWFIXED | LBS_OWNERDRAWVARIABLE));
That is the CCheckListBox must be owner-drawn. Find the CCheckListBox constructor code above, you will notice that it calls the CListBox (parent-class) constructor, applying either of the two owner-drawn styles. Instead, the CListBox constructor calls CWnd::Create() with the "LISTBOX" Windows Class-Name as a parameter. That is, it seems to be a MFC-implemented control, overriding the CListBox class, with an owner-drawn style. There is no mention of a native "Check-ListBox" class or style in the Win32 documentation either. Also the CCheckListBox documentation (in the link you posted) clearly states: CCheckListBox is only for owner-drawn controls because the list contains more than text strings.
Therefore:
If you are creating the control using a resource script, add an owner-drawn style (eg LBS_OWNERDRAWFIXED) to the control (or set the Owner-Drawn property in the property editor).
If you are creating the control programmatically make sure you are calling the CCheckListBox constructor, not the CListBox one.
Not sure what you mean about the scroll-bar (and why you mention it), doesn't the list-box display a scroll-bar automatically (WS_VSCROLL style - or property), do you have to do something on your own?
EDIT:
Forgot to mention, if you are creating the control using a resource script use the Class Wizard to add a member variable (of "Control" type, not "Value") to the dialog class. The new variable must be of type CCheckListBox (MFC class). This will subclass the control. If the old project already had a CListBox member variable change it to CCheckListBox.
I am using Visual Studio 2019 and building a C++ desktop application. I have a dialog class inherited from CDialogEx. In this class I have a few buttons, i.e. CButton as members.
When I use the EnableWindow method in the class constructor, it reports:
Debug Assertion Failed! Program C:\WINDOWS\SYSTEM32\mfc140ud.dll File:
d....\winocc.cpp line 345
If I commented it out the application worked fine. Any idea why I have this error? All I wanted to do is to disable the buttons as soon as the dialog shows up - that is why I use this method in the constructor.
There is a difference between a C++ class and the actual creation of the dialog window and its controls.
The constructor is for class related items, not window related items. For example, if you want to initialize member variables, then the constructor would be the place for it. But at construction, no dialog window has been created, thus there are no child controls that exist, thus the error you're seeing.
The place where you can assume that the window is created is in the dialog's OnInitDialog member function. This is where you should be able to call EnableWindow on the controls.
If you do not have an OnInitDialog, you can add that function using the class wizard.
I'm turning mad with a little problem with Visual Studio 2008 and MFC. I'm working on a project actually and I'm trying to create an SDI Application. Right, now I want to add a dockable DialogBar. Well, the first time I added it with the resource view, I could create the bar without problems.
But... I want to add some controls like a couple of ListBox, buttons and so on. The program doesn't allows me to create member variables for these controls. The option appears in grey.
Searching a little, I found that it's mandatory to create a new class derived from CDialogBar and "enhance" it with the Message handler and so on. I've been reading some tutorials and it didn't work for me.
Can you please help me? I'm starting to get nervous, the use of dialogbars is mandatory in my design and I've never implemented them before.
Thank you very much, and sorry for my poor english.
You can add a control member variable by hand instead of using the wizard. All it takes is a call to DDX_Control in the dialog bar's DoDataExchange function.
But CDialogBar-derived classes do not handle control clicks. The CDialogBar class forwards all of those messages to the dialog bar's parent window. So be prepared to add the message handlers to the parent (usually CMainFrame).
For learning purposes you might try creating your dialog bar as a CDialog first, to see the proper code lines and message map entries supplied by the wizard. Then you can copy/move these details as appropriate into your actual code project.
I've got a Dialog-based Application.
By default Visual Studio created an App and a Dlg class.
In the App's InitInstance, to show the dialog box, there is a declaration CMyDlg dlg, then a dlg.DoModal().
My question is, how do I access dlg members from my other classes? For instance, I created an edit box with a control variable associated with it. I want one of my other classes to set the text of the edit box and display it.
Help much appreciated.
I've used MFC dialogs before where you do:
EnterNameDlg dlg;
dlg.DoModal();
string str = dlg.GetName();
However a dialog I have now actually looks at a list-box control in such a method and it's not working. Although the class instance clearly exists after DoModal(), does the actual dialog get destroyed? I noticed calling DoModal() a 2nd time leads to OnInitDialog() also being called again which seems to support this theory, the dialog is recreated from the template rather than simply made visible the 2nd time.
Yes, DoModal creates a dialog on each call and destroys the window before returning.
Only the data members will still be valid. Of course, you can add more data members in your EnterNameDlg class if you want to collect data during dialog's lifetime.
As soon as the dlg gets out of scope, everything will be deallocated.
After DoModal class instance still exists, but window and all its controls are destroyed. You can call only functions that don't work with dialog controls after DoModal. Inside of the dialog class, keep required values in class members like CString, when OK button is pressed. These members can be read after dialog is closed.
The entirety of MFC is built around an awkward pairing - the Windows window with its associated handle, and the MFC class object. The MFC classes are designed to outlast the window in most cases.