WxQt

Getting started

Prerequisites

Currently, wxQT needs Qt 5 or later (recommended version is Qt 5.2.1). Other dependencies are needed depending on the features to be used (fo example cairo, opengl, jpg/tiff, etc.). For more information see docs/qt folder shipped with the source code, and/or Ubuntu / Android notes.

Building the Library

Go to your development directory and download the source code zip archive or checkout the current wxQT repository ("Google Summer of Code 2014" Qt branch) with:

git clone https://github.com/reingart/wxWidgets.git -b SOC2014_QT
cd wxWidgets

Now create the build directory e.g.: 'bldqt5' and from it call the configure script (using Qt option) and run make to start the compilation process:

mkdir bldqt5
cd bldqt5
../configure --with-qt --enable-debug
make

Building Samples, Tests and Demos

After successful build, you can go to the samples sub-directory, compile and run them, for example:

cd samples/controls
make
./controls

You can also try the tests and demos sub-directories.

Architecture

Internals

wxQT uses the same techniques like in other ports to wrap the Qt toolkit classes inside the wxWidget hierachy.

An internal pointer m_qtWindow in wxWindow holds the reference to the QWidget (or derived) counterpart, and is accesible through the virtual method `GetHandle`. This pointer and other window styles are set up in the `PostCreation` method that must be called by the derived classes (mostly controls) to initialize the widget correctly. Not doing so will cause painting and deletion issues, as the base class will not know how to handle the Qt widget. wxControl even provides a protected method QtCreateControl that will do the common initialization (including post creation step).

Warning: Take care of not calling any function that can raise an assertion before `PostCreation`, for example wxFAIL_MSG, as it will interrupt the normal initialization, hence the later cleanup will crash. For example, this issue was caused by WXValidateStyle in wxCheckBox::Create, that was "failing silently" in unit tests, and then raising segmentation faults when the object was later deleted (as Qt checkbox counterpart was never being deleted due the aborted initialization).

Many controls have also other pointers to allow to map different sub-widgets and other features. In the other end, Top Level Windows (frames and dialogs) uses directly the internal window pointer, doing a static cast to return the correct type for `GetHandle`, avoiding multilevel pointer hierarchies. This would be the ideal solution, but not all classes could be mapped 1:1 and that could introduce potential issues (i.e. invalid static casts) and more boilerplate due to additional specific accesor methods.

Note that some special cases are not real windows like the `wxTabFrame` (AUI), so they don't set the internal pointer and hence drawing methods should not be used at all.

Many wxWidgets classes maps 1:1 to Qt ones, but there are some exceptions are (1:N or N:1):

• wxAnyButton (wxButton, wxBitmapButton, wxToggleButton): QPushButton
• wxFrame: QMainWindow with a QWidget inside as central widget
• wxRadioBox: QGroupBox with a QButtonGroup inside
• wxStaticText & wxStaticBitmap: QLabel
• wxTextCtrl: QLineEdit or QTextEdit (multiline)
• wxWindow (wxPanel): QWidget or QScrollArea

Private helpers

Qt objects needs to be sub-classed to re-implement the events and connect signals:

• Qt events are just virtual methods that needs to be overridden by the derived classes to handle them
• Qt signals can be connected to QObject members or simple functions (thanks to Qt5 new signal slot syntax)

The approach chosen was to use templates to help inherit QObject's (QWidget), providing a common base to handle events and signal infrastructure:

• wxQtSignalHandler< wxWindow >: allows emitting wx events for Qt events & signals. This should be used used for all QObjects derivatives that are not widgets, for example QAction (used for shortcut / accelerators).
• wxQtEventSignalHandler< QWidget, wxWindow >: derived from `wxQtSignalHandler`, also handles basic events (change, focus, mouse, keyboard, paint, close, etc.). This should be used for all QWidget derivatives (controls, top level windows, etc.)

Both templates also have some safety checks to avoid invalid spurious access to deleted wx objects (using a special pointer to the wx instance stored in the Qt object, that is reseted to NULL when the wx counterpart is deleted). This is due that in some situations, Qt object could still be referenced in the Qt event queue, so it cannot be removed immediately.

Note that no public wxWidget class should be derived directly from QWidget as they could have different lifespans and other implications to run time type systems (RTTI). Some QObjects are even owned by Qt (for example: menubar, statusbar) and some parents (ie. `QTabWidget`) cannot be deleted immediately in some circumstances (they would cause segmentation faults due spurious events / signals caused by the children destruction if not correctly handled as explained previously)

For more information about the deletion issues, see deleteLater notes.

Files Structure

Although some Qt headers are included in public wx headers, this dependencies should be avoided as this could change in the future (decoupling completely the public wxQT headers from Qt).

Adding files

To add a Qt derived class simply put it in a .h file and add the corresponding .cpp file to the build/bakefiles/files.bkl e.g.:

<set var="QT_LOWLEVEL_HDR" hints="files">
    wx/qt/menuitem.h
</set>

<set var="QT_LOWLEVEL_SRC" hints="files">
    src/qt/menuitem.cpp
</set>

From within of the bakefiles directory, regenerate the autoconf files with:

bakefile_gen --formats autoconf

Generate the 'configure' script in your wxQt root directory with:

autoconf

IMPORTANT NOTE: The precompilation step (Qt's moc) is no more needed so the build rule was removed. There is no need to use Q_OBJECT nor Q_SLOTS macros.

// include/wx/qt/menuitem.h

class wxMenuItem : public wxMenuItemBase
{
   // ...
};

class wxQtAction : public QAction
{
public:
    wxQtAction( wxMenuItem *menuItem, const QString &text, QObject *parent );

private:
    void OnActionTriggered( bool checked );

private:
    wxMenuItem *m_menuItem;
};

Coding guidelines

• If you leave out an implementation for whatever reason, then mark it with the wxMISSING_IMPLEMENTATION() macro from wx/qt/utils.h i.e.:

void wxSomeClass::SomeMethod()
{
    wxMISSING_IMPLEMENTATION( __FUNCTION__ );
}

or if only some implementation is missing like evaluating flags:

void wxSomeClass::SomeMethod( unsigned methodFlags )
{
    wxMISSING_IMPLEMENTATION( "methodFlags" );
}

• To avoid name clashes with a 3rd party library like boost, and due precompilation step was removed, don't use the internal moc keywords 'signals' and 'slots':

class wxQtClass : public QClass
{
private:
    void OnSignal();
};

Naming conventions

• Global helper classes and global functions should be prefixed with 'wxQt' i.e.:

class wxQtButton : public QPushButton
{
}

QRect wxQtConvertRect( const wxRect & );

• Internal methods in publicly visible classes (like wxWindow) should be prefixed with 'Qt' i.e.:

class wxWindow : public wxWindowBase
{
public:
    QWidget *QtGetContainer() const;
};

Port status

A table attempting to summarize progress in the port can be found at WxQt/Status.

I (Peter Most) can be contacted on the developer mailing list.