Standalone FileDialog window with wxWidgets - c++

Question

I'm trying to use wxWidgets to create a open/save FileDialog window in a cross-platform way. So I've looked at the examples in the documentation. I also want to create standalone windows, with no parent, because I am not using any other instance of a wxApp/wxWindow elsewhere in my program.
Additionally, I need to have my own main function, so I don't want to use a macro such as IMPLEMENT_APP. I tried to follow the instructions given here, and came up with the following minimal program:
#include <wx/wx.h>
#include <string>
#include <iostream>
std::string openFile() {
wxFileDialog openFileDialog(NULL, _("Open XYZ file"), "", "",
"XYZ files (*.xyz)|*.xyz", wxFD_OPEN|wxFD_FILE_MUST_EXIST);
if (openFileDialog.Show() == wxID_CANCEL)
return ""; // the user changed idea...
// proceed loading the file chosen by the user;
return "something";
}
int main(int argc, char *argv[]) {
std::cout << wxEntryStart(argc, argv) << std::endl;
std::string s = openFile();
wxEntryCleanup();
}
And here is the CMakeLists.txt I used to compile the code:
CMake_Minimum_Required(VERSION 2.8.11)
Project(test)
Find_Package(wxWidgets REQUIRED)
Include(${wxWidgets_USE_FILE})
Add_Executable(test main.cpp)
Target_Link_Libraries(test ${wxWidgets_LIBRARIES})
Still, when I run this program, I get a Segmentation Fault, despite the wxEntryStart returning true, and I have no idea where the problem comes from. Any tip?

Answer 1

I wouldn't be so bold with stripping down wx's initialization code. It may work today, but in the next version, who knows...
This is what I use:
class MyApp : public wxApp { };
wxIMPLEMENT_APP_NO_MAIN(MyApp);
int main()
{
wxDISABLE_DEBUG_SUPPORT();
int dummy = 0;
if(!wxEntryStart(dummy, static_cast<wxChar**>(nullptr)))
return 1;
auto onx1 = on_exit([]{ wxEntryCleanup(); }); //using RAII for cleanup
//Other initialization, create main window, show it.
wxGetApp().OnRun(); //This starts the event loop.
//In your case, it looks like ShowModal's event loop is enough,
//so you don't need this.
}
I think those macros, ugly as they are, provide much better insulation against future changes in the library initialization code.

Answer 2

Ok, after some fiddling here is a code sample that works for me. Comments welcome on what'd be the best practices. What I did was keep ShowModal() instead of Show() in the openFile function. I also created the instance of singleton wxApp. The final code is here:
#include <wx/wx.h>
#include <string>
#include <iostream>
std::string openFile() {
wxFileDialog openFileDialog(NULL, _("Open XYZ file"), "", "",
"XYZ files (*.xyz)|*.xyz", wxFD_OPEN|wxFD_FILE_MUST_EXIST);
if (openFileDialog.ShowModal() == wxID_CANCEL)
return ""; // the user changed idea...
// proceed loading the file chosen by the user;
return "something";
}
int main(int argc, char *argv[]) {
wxApp::SetInstance( new wxApp() );
wxEntryStart(argc, argv);
std::string s = openFile();
wxEntryCleanup();
}
Not sure this is completely leak-free, as valgrind seems to complain a little after exit. Any tip about whether I could also put the wxEntryStart() in the openFile() function welcome (I am guaranteed that this is the only place where the wxWidgets lib is used, and I want an API as simple as possible).