App crashes on AppendCollumn() with a Virtual List Control

Question

I am a hobby programmer still learning C++ and wxWidgets. I use Code::Blocks 20.3, wxWidgets 3.1.4, and MinGW 17.1 on a Windows 10 Pro computer.

I am trying to make a virtual wxListCtrl work in Code::Blocks, I followed the code in the ListCtrl sample and a simple example in the wxWidgets Discussion Forum. The sample (1 file) code on both compiles and works. When I start a new project in Code::Blocks, the GUI APP and MAIN is coded in separate files. Perhaps I need to do more, but cannot find what it is. The project compiles with zero errors and warnings, but it shows below error on startup. I tried moving SetItemCount() above AppendCollumn(), but that did not help. There is no error when I comment both AppendColumn() out, but then of course the list is empty.

Can someone please help me with what is missing in my code?

Thank you, Ruud

Error:

A debugging check in this application has failed
../../src/cpmmon.listctrlcmn.cpp(259):
 assert "Assert Failure" failed in OnGetItemText():
 wxListCtrl::OnGetItemText not supposed to be called

GUI code:

GUIFrame::GUIFrame( wxWindow* parent, wxWindowID id, const wxString& title, const wxPoint& pos, const wxSize& size, long style ) : wxFrame( parent, id, title, pos, size, style )
{
    this->SetSizeHints( wxDefaultSize, wxDefaultSize );

    wxBoxSizer* bSizer1;
    bSizer1 = new wxBoxSizer( wxVERTICAL );

    m_listCtrl1 = new wxListCtrl( this, wxID_ANY, wxDefaultPosition, wxDefaultSize, wxLC_REPORT|wxLC_VIRTUAL );
    bSizer1->Add( m_listCtrl1, 1, wxALL|wxEXPAND, 10 );

    this->SetSizer( bSizer1 );
    this->Layout();

    // Connect Events
    this->Connect( wxEVT_CLOSE_WINDOW, wxCloseEventHandler( GUIFrame::OnClose ) );
}

GUIFrame::~GUIFrame()
{
    // Disconnect Events
    this->Disconnect( wxEVT_CLOSE_WINDOW, wxCloseEventHandler( GUIFrame::OnClose ) );
}

Main Code:

#include "VlistMain.h"

const wxChar *SMALL_VIRTUAL_VIEW_ITEMS[][2] =
{
    { wxT("Cat"), wxT("meow") },
    { wxT("Sheep"), wxT("baaah") }
};

VlistFrame::VlistFrame(wxFrame *frame) : GUIFrame(frame)
{
    m_listCtrl1->AppendColumn("Animal");
    m_listCtrl1->AppendColumn("Sound");
    m_listCtrl1->SetItemCount(WXSIZEOF(SMALL_VIRTUAL_VIEW_ITEMS));
}

wxString VlistFrame::OnGetItemText(long item, long column) const
{
    return SMALL_VIRTUAL_VIEW_ITEMS[item][column];
}

Event table:

wxBEGIN_EVENT_TABLE(MyListCtrl, wxListCtrl)
    EVT_LIST_ITEM_SELECTED(wxAny, MyListCtrl::OnSelected)
wxEND_EVENT_TABLE()

Answer 1

Here's a second answer that uses wxFormbuilder's subclass feature. The advantage of this approach is that it will let you set up event handlers with wxFormbuilder. First we'll need to have a slightly different declaration for the constructor for the derived class

class MyListCtrl:public wxListCtrl
{
public:
    MyListCtrl(wxWindow *parent,
               wxWindowID id,
               const wxPoint& pos = wxDefaultPosition,
               const wxSize& size = wxDefaultSize,
               long style = wxLC_VIRTUAL | wxLC_REPORT);
    virtual wxString OnGetItemText(long item, long column) const wxOVERRIDE;
};

This add's more parameters to the constructor so that it will be compatible with the code generated by wxFormbuilder. As in the other answer, this should be placed in a new header file that is added to the project.

Next in a code file, add the body for the constructor

MyListCtrl::MyListCtrl(wxWindow *parent, wxWindowID id, const wxPoint& pos,
                       const wxSize& size, long style)
           :wxListCtrl(parent, id, pos, size,
                       wxLC_VIRTUAL | wxLC_REPORT, wxDefaultValidator,
                       "MyListCtrl")
{

}

Note that this forces the the subclass to have the style wxLC_VIRTUAL | wxLC_REPORT and will ignore any style entered in wxFormbuilder. So if you want to change the style, you should change it in the code above.

Alternately you could change wxLC_VIRTUAL | wxLC_REPORT to style. Then the style options entered in wxFormbuilder will be used. But then it's up to you to make sure those options always include wxLC_REPORT and wxLC_VIRTUAL and do not contain any other options that are incompatible with those two.

Next, in wxFormbuilder, add a list control to your form and on the object properties tab, set the subclass options to

name: MyListCtrl
header: MyLstCtrl.h

(you can leave the forward_declare option checked or unchecked - it doesn't make any difference).

Now you can add any event handlers for your list control just like with any other widget:

Answer 2

To use a virtual list control, you need to derive a class from wxListCtrl and override the OnGetItemText method. For example:

class MyListCtrl:public wxListCtrl
{
public:
    MyListCtrl(wxWindow *parent, wxWindowID id);
    virtual wxString OnGetItemText (long item, long column) const wxOVERRIDE;
};

MyListCtrl::MyListCtrl(wxWindow *parent, wxWindowID id)
           :wxListCtrl(parent, id, wxDefaultPosition, wxDefaultSize,
                       wxLC_VIRTUAL | wxLC_REPORT, wxDefaultValidator,
                       "MyListCtrl")
{

}

wxString MyListCtrl::OnGetItemText(long item, long column) const
{
    return SMALL_VIRTUAL_VIEW_ITEMS[item][column];
}

You can also override OnGetItemColumnImage and OnGetItemAttr to further customize your control.

---

Since it looks like you're using wxFormbuilder, you can do this using the Custom Control widget. To do this, first you need to add a new header file to your project named MyListCtrl.h (or whatever you want to call it). The contents of the new header should look something like this:

#ifndef MYLISTCTRL_H_INCLUDED
#define MYLISTCTRL_H_INCLUDED

#include <wx/listctrl.h>

class MyListCtrl:public wxListCtrl
{
public:
    MyListCtrl(wxWindow *parent, wxWindowID id);
    virtual wxString OnGetItemText (long item, long column) const wxOVERRIDE;
};

#endif // MYLISTCTRL_H_INCLUDED

Once you have the header for your control, you can use the "CustomControl" widget. It's the second to last item on the Additional tab:

On the properties tab, you'll need to set the following items

name:          m_listCtrl1
declaration:   MyListCtrl* m_listCtrl1;
construction:  m_listCtrl1 = new MyListCtrl(m_panel1, wxID_ANY);
include:       #include "MyListCtrl.h"

like so:

You can the provide the code for the MyListCtrl::MyListCtrl constructor and MyListCtrl::OnGetItemText in the same file as your devived frame class. Or if you want maintain one class per file, you can also put it in a new cpp file. Obviously you need to add "#include "MyListCtrl.h" at the top of which ever file you use to put the code for those methods in.

---

To handle events using event tables, you would need to add declarations for the event handling methods and the wxDECLARE_EVENT_TABLE macro to the class declaration.

class MyListCtrl:public wxListCtrl
{
public:
    MyListCtrl(wxWindow *parent, wxWindowID id);
    virtual wxString OnGetItemText (long item, long column) const wxOVERRIDE;

protected:
    void OnItemSelected(wxListEvent& event);
    // Add all other event handler method declarations here
private:
    wxDECLARE_EVENT_TABLE();
};

Then in the file with the code you would have something like:

wxBEGIN_EVENT_TABLE(MyListCtrl, wxListCtrl)
    EVT_LIST_ITEM_SELECTED(wxID_ANY, MyListCtrl::OnItemSelected)
    /* Add all other event macros here */
wxEND_EVENT_TABLE()


void MyListCtrl::OnItemSelected(wxListEvent& event)
{
    // do something here
}

// write all other event handlers here.

---

On a personal note, I really don't like event tables, so I would use dynamic event binding instead. To do this, the declaration for the class should look something like this:

class MyListCtrl:public wxListCtrl
{
public:
    MyListCtrl(wxWindow *parent, wxWindowID id);
    virtual wxString OnGetItemText (long item, long column) const wxOVERRIDE;

protected:
    void OnItemSelected(wxListEvent& event);
    // declare all other event handlers here.
};

Then the code for the constructor should look something like this:

MyListCtrl::MyListCtrl(wxWindow *parent, wxWindowID id)
           :wxListCtrl(parent, id, wxDefaultPosition, wxDefaultSize,
                       wxLC_VIRTUAL | wxLC_REPORT, wxDefaultValidator,
                       "MyListCtrl")
{
    Bind(wxEVT_LIST_ITEM_SELECTED, &MyListCtrl::OnItemSelected, this);
    // Add any other needed Bind statements here
}