Get rid of QtCreateControl() from wxQt code base

If possible, all windows should call wxWindow::Create() on creation now,
because among other things:
- It manages generic and non-generic windows uniformly and transparently
- It ensures an appropriate initial size for the window
- AddChild() and PostCreation() are automatically called
- Scrollbar policies are set in one place.

include/wx/qt/control.h

@@ -24,13 +24,6 @@ public:
             const wxValidator& validator = wxDefaultValidator,
             const wxString& name = wxASCII_STR(wxControlNameStr));
 
-    virtual wxSize DoGetBestSize() const override;
-
-protected:
-    bool QtCreateControl( wxWindow *parent, wxWindowID id, const wxPoint &pos,
-        const wxSize &size, long style, const wxValidator &validator,
-        const wxString &name );
-
 private:
     wxDECLARE_DYNAMIC_CLASS(wxControl);
 };

include/wx/qt/frame.h

@@ -13,7 +13,6 @@
 #include "wx/frame.h"
 
 class QMainWindow;
-class QAbstractScrollArea;
 
 class WXDLLIMPEXP_CORE wxFrame : public wxFrameBase
 {

include/wx/qt/listbox.h

@@ -10,7 +10,6 @@
 
 class QListWidget;
 class QModelIndex;
-class QAbstractScrollArea;
 
 class WXDLLIMPEXP_CORE wxListBox : public wxListBoxBase
 {

include/wx/qt/textctrl.h

@@ -8,7 +8,6 @@
 #ifndef _WX_QT_TEXTCTRL_H_
 #define _WX_QT_TEXTCTRL_H_
 
-class QAbstractScrollArea;
 class wxQtEdit;
 
 class WXDLLIMPEXP_CORE wxTextCtrl : public wxTextCtrlBase

include/wx/qt/window.h

@@ -66,7 +66,8 @@ public:
                 long style = 0,
                 const wxString& name = wxASCII_STR(wxPanelNameStr));
 
-    // Used by all window classes in the widget creation process.
+    // Derived classes have to call PostCreation() explicitly if they don't call
+    // our Create() method during widget creation process.
     void PostCreation( bool generic = true );
 
     void AddChild( wxWindowBase *child ) override;
@@ -202,6 +203,8 @@ protected:
     virtual void DoSetClientSize(int width, int height) override;
     virtual void DoGetClientSize(int *width, int *height) const override;
 
+    virtual wxSize DoGetBestSize() const override;
+
     virtual void DoMoveWindow(int x, int y, int width, int height) override;
 
 #if wxUSE_TOOLTIPS

src/qt/button.cpp

@@ -44,7 +44,7 @@ bool wxButton::Create(wxWindow *parent, wxWindowID id,
     QtCreate(parent);
     SetLabel( label.IsEmpty() && wxIsStockID( id ) ? wxGetStockLabel( id ) : label );
 
-    return QtCreateControl( parent, id, pos, size, style, validator, name );
+    return wxButtonBase::Create( parent, id, pos, size, style, validator, name );
 }
 
 wxWindow *wxButton::SetDefault()

src/qt/calctrl.cpp

@@ -96,7 +96,7 @@ bool wxCalendarCtrl::Create(wxWindow *parent, wxWindowID id, const wxDateTime& d
     if ( date.IsValid() )
         SetDate(date);
 
-    return QtCreateControl( parent, id, pos, size, style, wxDefaultValidator, name );
+    return wxCalendarCtrlBase::Create( parent, id, pos, size, style, wxDefaultValidator, name );
 }
 
 void wxCalendarCtrl::UpdateStyle()

src/qt/checkbox.cpp

@@ -66,7 +66,7 @@ bool wxCheckBox::Create(wxWindow *parent, wxWindowID id, const wxString& label,
     m_qtCheckBox->setText( wxQtConvertString( label ) );
 
     // Do the initialization here as WXValidateStyle may fail in unit tests
-    bool ok = QtCreateControl( parent, id, pos, size, style, validator, name );
+    bool ok = wxCheckBoxBase::Create( parent, id, pos, size, style, validator, name );
 
     WXValidateStyle(&style);
 

src/qt/choice.cpp

@@ -138,7 +138,7 @@ bool wxChoice::Create( wxWindow *parent, wxWindowID id,
     while ( n-- > 0 )
         m_qtComboBox->addItem( wxQtConvertString( *choices++ ));
 
-    return QtCreateControl( parent, id, pos, size, style, validator, name );
+    return wxChoiceBase::Create( parent, id, pos, size, style, validator, name );
 }
 
 wxSize wxChoice::DoGetBestSize() const

src/qt/combobox.cpp

@@ -149,7 +149,7 @@ bool wxComboBox::Create(wxWindow *parent, wxWindowID id,
         m_qtComboBox->addItem( wxQtConvertString( *choices++ ));
     m_qtComboBox->setCurrentText( wxQtConvertString( value ));
 
-    return QtCreateControl( parent, id, pos, size, style, validator, name );
+    return wxChoiceBase::Create( parent, id, pos, size, style, validator, name );
 }
 
 bool wxComboBox::IsReadOnly() const

src/qt/control.cpp

@@ -43,37 +43,3 @@ bool wxControl::Create(wxWindow *parent, wxWindowID id,
 
     return isCreated;
 }
-
-bool wxControl::QtCreateControl( wxWindow *parent, wxWindowID id,
-    const wxPoint &pos, const wxSize &size, long style,
-    const wxValidator &validator, const wxString &name )
-{
-    // The Qt widget has been created without a position/size so move/resize it:
-
-    wxSize bestSize = GetBestSize();
-    int width = ( size.GetWidth() == wxDefaultCoord ) ? bestSize.GetWidth() : size.GetWidth();
-    int height = ( size.GetHeight() == wxDefaultCoord ) ? bestSize.GetHeight() : size.GetHeight();
-
-    DoMoveWindow( pos.x, pos.y, width, height );
-
-    // Let Qt handle the background:
-    SetBackgroundStyle(wxBG_STYLE_SYSTEM);
-
-    if (!CreateControl( parent, id, pos, size, style, validator, name ))
-        return false;
-
-    PostCreation(false);
-    return true;
-}
-
-wxSize wxControl::DoGetBestSize() const
-{
-    wxSize minsize = wxQtConvertSize( GetHandle()->minimumSizeHint() );
-    wxSize size = wxQtConvertSize( GetHandle()->sizeHint() );
-    // best effort to ensure a correct size (note that some qt controls implement just one or both size hints)
-    if (size.GetWidth() < minsize.GetWidth())
-        size.SetWidth(minsize.GetWidth());
-    if (size.GetHeight() < minsize.GetHeight())
-        size.SetHeight(minsize.GetHeight());
-    return size;
-}

src/qt/datectrl.cpp

@@ -74,7 +74,7 @@ wxDatePickerCtrl::Create(wxWindow *parent,
     m_qtDateEdit->setCalendarPopup(style & wxDP_DROPDOWN);
     m_qtDateEdit->setDisplayFormat(QLocale::system().dateFormat(QLocale::ShortFormat));
 
-    return QtCreateControl( parent, id, pos, size, style, validator, name );
+    return wxDatePickerCtrlBase::Create( parent, id, pos, size, style, validator, name );
 }
 
 // ----------------------------------------------------------------------------

src/qt/dialog.cpp

@@ -70,12 +70,7 @@ bool wxDialog::Create( wxWindow *parent, wxWindowID id,
         m_qtWindow->setWindowFlags(qtFlags);
     }
 
-    if ( !wxTopLevelWindow::Create( parent, id, title, pos, size, style, name ) )
-        return false;
-
-    PostCreation();
-
-    return true;
+    return wxTopLevelWindow::Create( parent, id, title, pos, size, style, name );
 }
 
 int wxDialog::ShowModal()

src/qt/frame.cpp

@@ -60,13 +60,16 @@ bool wxFrame::Create( wxWindow *parent, wxWindowID id, const wxString& title,
 
     // QMainWindow takes ownership of the central widget pointer.
     // Not using QScrollArea or wxPanel is intentional here as it makes the
-    // implementation simpler and manageable.
+    // implementation simpler and more manageable.
     GetQMainWindow()->setCentralWidget( new wxQtCentralWidget( this, this ) );
 
     if ( !wxFrameBase::Create( parent, id, title, pos, size, style, name ) )
+    {
         return false;
+    }
+
+    SetWindowStyleFlag(style);
 
-    PostCreation();
     return true;
 }
 
@@ -97,8 +100,6 @@ void wxFrame::SetStatusBar( wxStatusBar *statusBar )
     if ( statusBar != nullptr )
     {
         GetQMainWindow()->setStatusBar( statusBar->GetQStatusBar() );
-        // Update statusbar sizes now that it has a size
-        statusBar->Refresh();
     }
     else
     {
@@ -213,35 +214,12 @@ void wxFrame::RemoveChild( wxWindowBase *child )
 // excluding any menubar and toolbar if any.
 wxPoint wxFrame::GetClientAreaOrigin() const
 {
-    wxPoint pt = wxFrameBase::GetClientAreaOrigin();
-
-#if wxUSE_MENUBAR
-    wxMenuBar * const menubar = GetMenuBar();
-    if ( menubar && menubar->IsAttached() )
-        pt.y += menubar->GetSize().y;
-#endif // wxUSE_MENUBAR
-
-    return pt;
+    return wxQtConvertPoint( GetQMainWindow()->centralWidget()->pos() );
 }
 
 void wxFrame::DoGetClientSize(int *width, int *height) const
 {
-    wxWindow::DoGetClientSize(width, height);
-
-    // Adjust the height, taking the status and menu bars into account, if any:
-    if ( height )
-    {
-        if ( wxStatusBar *sb = GetStatusBar() )
-        {
-            *height -= sb->GetSize().y;
-        }
-
-
-        if ( QWidget *qmb = GetQMainWindow()->menuWidget() )
-        {
-            *height -= qmb->geometry().height();
-        }
-    }
+    wxFrameBase::DoGetClientSize(width, height);
 }
 
 void wxFrame::DoSetClientSize(int width, int height)

src/qt/gauge.cpp

@@ -61,7 +61,7 @@ bool wxGauge::Create(wxWindow *parent,
     m_qtProgressBar->setTextVisible( style & wxGA_TEXT );
     m_qtProgressBar->setValue(0);
 
-    return QtCreateControl( parent, id, pos, size, style, validator, name );
+    return wxControl::Create( parent, id, pos, size, style, validator, name );
 }
 
 

src/qt/listbox.cpp

@@ -137,7 +137,9 @@ bool wxListBox::Create(wxWindow *parent, wxWindowID id,
         }
         m_qtListWidget->addItem(item);
     }
-    return wxListBoxBase::Create( parent, id, pos, size, style, validator, name );
+    return wxListBoxBase::Create( parent, id, pos, size,
+                                  style | wxVSCROLL | wxHSCROLL,
+                                  validator, name );
 }
 
 bool wxListBox::Create(wxWindow *parent, wxWindowID id,
@@ -170,7 +172,9 @@ bool wxListBox::Create(wxWindow *parent, wxWindowID id,
         m_qtListWidget->addItem(item);
     }
 
-    return wxListBoxBase::Create( parent, id, pos, size, style, validator, name );
+    return wxListBoxBase::Create( parent, id, pos, size,
+                                  style | wxVSCROLL | wxHSCROLL,
+                                  validator, name );
 }
 
 void wxListBox::DoCreate(wxWindow* parent, long style)
@@ -178,7 +182,6 @@ void wxListBox::DoCreate(wxWindow* parent, long style)
     Init();
 
     m_qtWindow =
-    m_qtContainer =
     m_qtListWidget = new wxQtListWidget( parent, this );
 
     if ( style & wxLB_SORT )

src/qt/listctrl.cpp

@@ -1347,6 +1347,7 @@ bool wxListCtrl::Create(wxWindow *parent,
         ? new wxQtVirtualListModel(this)
         : new wxQtListModel(this);
 
+    m_qtWindow =
     m_qtTreeWidget = new wxQtListTreeWidget(parent, this);
     m_qtTreeWidget->setModel(m_model);
     m_model->SetView(m_qtTreeWidget);
@@ -1355,7 +1356,9 @@ bool wxListCtrl::Create(wxWindow *parent,
     m_qtTreeWidget->setSelectionBehavior(QAbstractItemView::SelectRows);
     m_qtTreeWidget->setTabKeyNavigation(true);
 
-    if ( !QtCreateControl(parent, id, pos, size, style, validator, name) )
+    if ( !wxListCtrlBase::Create(parent, id, pos, size,
+                                 style | wxVSCROLL | wxHSCROLL,
+                                 validator, name) )
         return false;
 
     SetWindowStyleFlag(style);

src/qt/menu.cpp

@@ -213,23 +213,25 @@ QMenu *wxMenu::GetHandle() const
 wxMenuBar::wxMenuBar()
 {
     m_qtMenuBar  = new QMenuBar();
-    PostCreation(false);
+
+    wxMenuBarBase::Create(nullptr, wxID_ANY);
 }
 
-wxMenuBar::wxMenuBar( long WXUNUSED( style ))
+wxMenuBar::wxMenuBar( long style )
 {
     m_qtMenuBar = new QMenuBar();
-    PostCreation(false);
+
+    wxMenuBarBase::Create(nullptr, wxID_ANY, wxDefaultPosition, wxDefaultSize, style);
 }
 
-wxMenuBar::wxMenuBar(size_t count, wxMenu *menus[], const wxString titles[], long WXUNUSED( style ))
+wxMenuBar::wxMenuBar(size_t count, wxMenu *menus[], const wxString titles[], long style)
 {
     m_qtMenuBar = new QMenuBar();
 
     for ( size_t i = 0; i < count; ++i )
         Append( menus[ i ], titles[ i ] );
 
-    PostCreation(false);
+    wxMenuBarBase::Create(nullptr, wxID_ANY, wxDefaultPosition, wxDefaultSize, style);
 }
 
 

src/qt/msgdlg.cpp

@@ -109,7 +109,7 @@ wxMessageDialog::wxMessageDialog( wxWindow *parent, const wxString& message,
     if ( style & wxSTAY_ON_TOP )
         dlg->setWindowModality( Qt::ApplicationModal );
 
-    PostCreation();
+    PostCreation(false);
 
     Centre(wxBOTH | wxCENTER_FRAME);
 }

src/qt/notebook.cpp

@@ -75,7 +75,7 @@ bool wxNotebook::Create(wxWindow *parent,
 {
     m_qtTabWidget = new wxQtTabWidget( parent, this );
 
-    if ( !QtCreateControl( parent, id, pos, size, style, wxDefaultValidator, name ) )
+    if ( !wxControl::Create( parent, id, pos, size, style, wxDefaultValidator, name ) )
         return false;
 
     if ( m_windowStyle & wxBK_RIGHT )

src/qt/radiobox.cpp

@@ -196,7 +196,7 @@ bool wxRadioBox::Create(wxWindow *parent,
     m_qtGroupBox->setLayout(horzLayout);
 
     SetMajorDim(majorDim == 0 ? n : majorDim, style);
-    return QtCreateControl( parent, id, pos, size, style, val, name );
+    return wxControl::Create( parent, id, pos, size, style, val, name );
 }
 
 static QAbstractButton *GetButtonAt( const QButtonGroup *group, unsigned int n )

src/qt/radiobut.cpp

@@ -127,7 +127,7 @@ bool wxRadioButton::Create( wxWindow *parent,
     m_qtRadioButton = new wxQtRadioButton( parent, this );
     m_qtRadioButton->setText( wxQtConvertString( label ));
 
-    if ( !QtCreateControl(parent, id, pos, size, style, validator, name) )
+    if ( !wxRadioButtonBase::Create(parent, id, pos, size, style, validator, name) )
         return false;
 
     // Check if we need to create a new button group: this must be done when

src/qt/scrolbar.cpp

@@ -52,7 +52,7 @@ bool wxScrollBar::Create( wxWindow *parent, wxWindowID id,
     m_qtScrollBar = new wxQtScrollBar( parent, this );
     m_qtScrollBar->setOrientation( wxQtConvertOrientation( style, wxSB_HORIZONTAL ));
 
-    return QtCreateControl( parent, id, pos, size, style, validator, name );
+    return wxScrollBarBase::Create( parent, id, pos, size, style, validator, name );
 }
 
 int wxScrollBar::GetThumbPosition() const

src/qt/slider.cpp

@@ -174,10 +174,10 @@ bool wxSlider::Create(wxWindow *parent,
     SetValue( value );
     SetPageSize(wxMax(1, (maxValue - minValue) / 10));
 
-    if ( !QtCreateControl( parent, id, pos, size, style, validator, name ) )
+    if ( !wxSliderBase::Create( parent, id, pos, size, style, validator, name ) )
         return false;
 
-    // SetTick() needs the window style which is normally set after QtCreateControl()
+    // SetTick() needs the window style which is normally set after wxSliderBase::Create()
     // is called. Pass 0 as tickPos parameter is not used by Qt anyhow.
     SetTick( 0 );
 

src/qt/spinbutt.cpp

@@ -91,7 +91,7 @@ bool wxSpinButton::Create(wxWindow *parent,
     wxSize newSize( size );
     newSize.SetWidth( 18 );
 
-    return QtCreateControl( parent, id, pos, newSize, style, wxDefaultValidator, name );
+    return wxSpinButtonBase::Create( parent, id, pos, newSize, style, wxDefaultValidator, name );
 }
 
 void wxSpinButton::SetRange(int min, int max)

src/qt/spinctrl.cpp

@@ -56,7 +56,7 @@ bool wxSpinCtrlQt< T, Widget >::Create( wxWindow *parent, wxWindowID id,
     if ( !value.IsEmpty() )
         SetValue( value );
 
-    return QtCreateControl( parent, id, pos, size, style, wxDefaultValidator, name );
+    return wxSpinCtrlBase::Create( parent, id, pos, size, style, wxDefaultValidator, name );
 }
 
 template< typename T, typename Widget >

src/qt/statbmp.cpp

@@ -52,7 +52,7 @@ bool wxStaticBitmap::Create( wxWindow *parent,
     m_qtLabel = new wxQtStaticBmp( parent, this );
     SetBitmap( label );
 
-    return QtCreateControl( parent, id, pos, size, style, wxDefaultValidator, name );
+    return wxStaticBitmapBase::Create( parent, id, pos, size, style, wxDefaultValidator, name );
 }
 
 static void SetPixmap( QLabel *label, const QPixmap *pixMap )

src/qt/statbox.cpp

@@ -48,7 +48,7 @@ bool wxStaticBox::Create(wxWindow *parent, wxWindowID id,
     m_qtGroupBox = new wxQtGroupBox( parent, this );
     m_qtGroupBox->setTitle( wxQtConvertString( label ) );
 
-    return QtCreateControl( parent, id, pos, size, style, wxDefaultValidator, name );
+    return wxStaticBoxBase::Create( parent, id, pos, size, style, wxDefaultValidator, name );
 }
 
 QWidget *wxStaticBox::GetHandle() const

src/qt/statline.cpp

@@ -40,7 +40,7 @@ bool wxStaticLine::Create( wxWindow *parent,
     else if ( style & wxLI_VERTICAL )
         m_qtFrame->setFrameStyle( QFrame::VLine );
 
-    return QtCreateControl( parent, id, pos, size, style, wxDefaultValidator, name );
+    return wxStaticLineBase::Create( parent, id, pos, size, style, wxDefaultValidator, name );
 }
 
 QWidget *wxStaticLine::GetHandle() const

src/qt/stattext.cpp

@@ -63,12 +63,9 @@ bool wxStaticText::Create(wxWindow *parent,
     else
         m_qtLabel->setAlignment(Qt::AlignLeft);
 
-    if ( !QtCreateControl(parent, id, pos, size, style, wxDefaultValidator, name) )
-        return false;
-
     SetLabel(label);
 
-    return true;
+    return wxStaticTextBase::Create(parent, id, pos, size, style, wxDefaultValidator, name);
 }
 
 void wxStaticText::SetLabel(const wxString& label)

src/qt/statusbar.cpp

@@ -43,15 +43,13 @@ bool wxStatusBar::Create(wxWindow *parent, wxWindowID id,
 {
     m_qtStatusBar = new wxQtStatusBar( parent, this );
 
-    if ( !QtCreateControl( parent, id, wxDefaultPosition, wxDefaultSize,
+    if ( !wxStatusBarBase::Create( parent, id, wxDefaultPosition, wxDefaultSize,
                            style, wxDefaultValidator, name ) )
         return false;
 
     if ( style & wxSTB_SIZEGRIP )
         m_qtStatusBar->setSizeGripEnabled(true);
 
-    PostCreation();
-
     SetFieldsCount(1);
 
     // Notice that child controls, if any, will be added using addWidget() in

src/qt/textctrl.cpp

@@ -676,19 +676,12 @@ bool wxTextCtrl::Create(wxWindow *parent,
 
     m_qtEdit->SetStyleFlags(style);
 
-    m_qtWindow =
-    m_qtContainer = m_qtEdit->ScrollBarsContainer();
+    m_qtWindow = m_qtEdit->ScrollBarsContainer();
 
-    if ( QtCreateControl( parent, id, pos, size, style, validator, name ) )
-    {
-        // set the initial text value without sending the event:
-        // (done here as needs CreateBase called to set flags for IsMultiLine)
-        ChangeValue( value );
-        // set the default inner color (white), as it is replaced by PostCreation
-        SetBackgroundColour( wxSystemSettingsNative::GetColour( wxSYS_COLOUR_LISTBOX ) );
-        return true;
-    }
-    return false;
+    // set the initial text value without sending the event
+    ChangeValue( value );
+
+    return wxTextCtrlBase::Create( parent, id, pos, size, style, validator, name );
 }
 
 wxTextCtrl::~wxTextCtrl()

src/qt/tglbtn.cpp

@@ -101,7 +101,7 @@ bool wxToggleButton::Create(wxWindow *parent,
     // this button is toggleable and has a text label
     SetLabel( wxIsStockID( id ) ? wxGetStockLabel( id ) : label );
 
-    return QtCreateControl( parent, id, pos, size, style, validator, name );
+    return wxToggleButtonBase::Create( parent, id, pos, size, style, validator, name );
 }
 
 void wxToggleButton::SetValue(bool state)

src/qt/timectrl.cpp

@@ -75,7 +75,7 @@ wxTimePickerCtrl::Create(wxWindow *parent,
                                           wxQtConvertTime(wxDateTime::Now()) );
     m_qtTimeEdit->setDisplayFormat(QLocale::system().timeFormat(QLocale::ShortFormat));
 
-    return QtCreateControl( parent, id, pos, size, style, validator, name );
+    return wxTimePickerCtrlBase::Create( parent, id, pos, size, style, validator, name );
 }
 
 // ----------------------------------------------------------------------------

src/qt/toolbar.cpp

@@ -167,15 +167,14 @@ bool wxToolBar::Create(wxWindow *parent, wxWindowID id, const wxPoint& pos,
     m_qtToolBar = new wxQtToolbar( parent, this );
     m_qtToolBar->setWindowTitle( wxQtConvertString( name ) );
 
+    if ( !wxControl::Create( parent, id, pos, size, style, wxDefaultValidator, name ) )
+    {
+        return false;
+    }
+
     SetWindowStyleFlag(style);
 
-    // not calling to wxWindow::Create, so do the rest of initialization:
-    if (parent)
-        parent->AddChild( this );
-
-    PostCreation();
-
-    return wxWindowBase::CreateBase( parent, id, pos, size, style, wxDefaultValidator, name );
+    return true;
 }
 
 wxToolBarToolBase *wxToolBar::FindToolForPosition(wxCoord WXUNUSED(x),

src/qt/toplevel.cpp

@@ -29,35 +29,23 @@ wxTopLevelWindowQt::wxTopLevelWindowQt(wxWindow *parent,
 }
 
 bool wxTopLevelWindowQt::Create( wxWindow *parent, wxWindowID winId,
-    const wxString &title, const wxPoint &pos, const wxSize &sizeOrig,
+    const wxString &title, const wxPoint &pos, const wxSize &size,
     long style, const wxString &name )
 {
-    wxSize size(sizeOrig);
-    if ( !size.IsFullySpecified() )
-        size.SetDefaults( GetDefaultSize() );
-
     wxTopLevelWindows.Append( this );
 
-    if (!CreateBase( parent, winId, pos, size, style, wxDefaultValidator, name ))
+    if (!wxWindow::Create( parent, winId, pos, size, style, name ))
     {
         wxFAIL_MSG( wxT("wxTopLevelWindowNative creation failed") );
         return false;
     }
 
-    SetTitle( title );
-    SetWindowStyleFlag( style );
-
-    if (pos != wxDefaultPosition)
-        m_qtWindow->move( pos.x, pos.y );
-
-    m_qtWindow->resize( wxQtConvertSize( size ) );
-
     // Prevent automatic deletion of Qt main window on close
     // (this should be the default, but left just fo enforce it)
     GetHandle()->setAttribute(Qt::WA_DeleteOnClose, false);
 
-    // not calling to wxWindow::Create, so do the rest of initialization:
-    if (parent) parent->AddChild( this );
+    SetTitle( title );
+    SetWindowStyleFlag( style );
 
     return true;
 }

src/qt/treectrl.cpp

@@ -573,14 +573,20 @@ bool wxTreeCtrl::Create(wxWindow *parent, wxWindowID id,
             const wxValidator& validator,
             const wxString& name)
 {
+    m_qtWindow =
     m_qtTreeWidget = new wxQTreeWidget(parent, this);
     m_qtTreeWidget->header()->hide();
 
-    SetWindowStyleFlag(style);
-
     Bind(wxEVT_KEY_DOWN, &wxTreeCtrl::OnKeyDown, this);
 
-    return QtCreateControl(parent, id, pos, size, style, validator, name);
+    if ( !wxTreeCtrlBase::Create(parent, id, pos, size, style|wxHSCROLL|wxVSCROLL, validator, name) )
+    {
+        return false;
+    }
+
+    SetWindowStyleFlag(style);
+
+    return true;
 }
 
 wxTreeCtrl::~wxTreeCtrl()

src/qt/window.cpp

@@ -16,6 +16,7 @@
 #include <QtWidgets/QApplication>
 #include <QtWidgets/QWidget>
 #include <QtWidgets/QScrollArea>
+#include <QtWidgets/QMainWindow>
 #include <QtWidgets/QMenu>
 #include <QtWidgets/QShortcut>
 
@@ -48,6 +49,15 @@ inline QWidget* wxQtGetDrawingWidget(QAbstractScrollArea* qtContainer,
 
     return qtWidget;
 }
+
+inline wxSize wxQtGetBestSize(QWidget* qtWidget)
+{
+    auto size = qtWidget->sizeHint();
+    // best effort to ensure a correct size (note that some qt controls
+    // implement just one or both size hints)
+    size = size.expandedTo(qtWidget->minimumSizeHint());
+    return wxQtConvertSize(size);
+}
 }
 
 // Base Widget helper (no scrollbar, used by wxWindow)
@@ -56,6 +66,19 @@ class wxQtWidget : public wxQtEventSignalHandler< QWidget, wxWindowQt >
 {
     public:
         wxQtWidget( wxWindowQt *parent, wxWindowQt *handler );
+
+        virtual QSize sizeHint() const override
+        {
+            // Make sure the window has a valid initial size because the default size of a
+            // generic control (e.g. wxPanel) is (0, 0) when created. Quoting the Qt docs:
+            //
+            //   "Setting the size to QSize(0, 0) will cause the widget
+            //    to not appear on screen. This also applies to windows."
+            //
+            // The value 20 seems to be the default for wxPanel under wxMSW.
+            return QSize(20, 20);
+        }
+
 };
 
 wxQtWidget::wxQtWidget( wxWindowQt *parent, wxWindowQt *handler )
@@ -361,55 +384,64 @@ bool wxWindowQt::Create( wxWindowQt * parent, wxWindowID id, const wxPoint & pos
     // that a generic control, like wxPanel, is being created, so we need a very
     // simple control as a base:
 
-    wxSize initialSize = size;
+    bool isGeneric = false;
 
     if ( GetHandle() == nullptr )
     {
+        isGeneric = true;
+
         if ( style & (wxHSCROLL | wxVSCROLL) )
         {
             m_qtWindow =
             m_qtContainer = new wxQtScrollArea( parent, this );
-
-            // If wx[HV]SCROLL is not given, the corresponding scrollbar is not shown
-            // at all. Otherwise it may be shown only on demand (default) or always, if
-            // the wxALWAYS_SHOW_SB is specified.
-            Qt::ScrollBarPolicy horzPolicy = (style & wxHSCROLL)
-                                              ? HasFlag(wxALWAYS_SHOW_SB)
-                                                  ? Qt::ScrollBarAlwaysOn
-                                                  : Qt::ScrollBarAsNeeded
-                                              : Qt::ScrollBarAlwaysOff;
-            Qt::ScrollBarPolicy vertPolicy = (style & wxVSCROLL)
-                                              ? HasFlag(wxALWAYS_SHOW_SB)
-                                                  ? Qt::ScrollBarAlwaysOn
-                                                  : Qt::ScrollBarAsNeeded
-                                              : Qt::ScrollBarAlwaysOff;
-
-            m_qtContainer->setHorizontalScrollBarPolicy( horzPolicy );
-            m_qtContainer->setVerticalScrollBarPolicy( vertPolicy );
         }
         else
+        {
             m_qtWindow = new wxQtWidget( parent, this );
+        }
+    }
+    else
+    {
+        m_qtContainer = dynamic_cast<QAbstractScrollArea*>(m_qtWindow);
+    }
 
-        // The default size of a generic control (e.g. wxPanel) is (0, 0) when created and
-        // is ignored by Qt unless the widget is already assigned a valid size or is added
-        // to a QLayout to be managed with. The value 20 seems to be the default under wxMSW.
-        // Do not pass 'initialSize' to CreateBase() below, as it will be taken as the minimum
-        // size of the control, which is not the intention here.
-        initialSize.SetDefaults(wxSize(20, 20));
+    if ( m_qtContainer )
+    {
+        // If wx[HV]SCROLL is not given, the corresponding scrollbar is not shown
+        // at all. Otherwise it may be shown only on demand (default) or always, if
+        // the wxALWAYS_SHOW_SB is specified.
+        Qt::ScrollBarPolicy horzPolicy = (style & wxHSCROLL)
+                                          ? HasFlag(wxALWAYS_SHOW_SB)
+                                              ? Qt::ScrollBarAlwaysOn
+                                              : Qt::ScrollBarAsNeeded
+                                          : Qt::ScrollBarAlwaysOff;
+        Qt::ScrollBarPolicy vertPolicy = (style & wxVSCROLL)
+                                          ? HasFlag(wxALWAYS_SHOW_SB)
+                                              ? Qt::ScrollBarAlwaysOn
+                                              : Qt::ScrollBarAsNeeded
+                                          : Qt::ScrollBarAlwaysOff;
+
+        m_qtContainer->setHorizontalScrollBarPolicy( horzPolicy );
+        m_qtContainer->setVerticalScrollBarPolicy( vertPolicy );
     }
 
     if ( !wxWindowBase::CreateBase( parent, id, pos, size, style, wxDefaultValidator, name ))
         return false;
 
-    parent->AddChild( this );
+    if ( parent )
+        parent->AddChild( this );
 
     wxPoint p;
     if ( pos != wxDefaultPosition )
         p = pos;
 
+    wxSize initialSize = size;
+    initialSize.SetDefaults( IsTopLevel() ? wxTopLevelWindowBase::GetDefaultSize()
+                                          : wxQtGetBestSize( GetHandle() ) );
+
     DoMoveWindow( p.x, p.y, initialSize.GetWidth(), initialSize.GetHeight() );
 
-    PostCreation();
+    PostCreation( isGeneric );
 
     return true;
 }
@@ -644,7 +676,6 @@ bool wxWindowQt::SetFont( const wxFont &font )
     if (GetHandle())
     {
         GetHandle()->setFont( font.GetHandle() );
-        return true;
     }
 
     return wxWindowBase::SetFont(font);
@@ -697,6 +728,10 @@ void wxWindowQt::DoGetTextExtent(const wxString& string, int *x, int *y, int *de
 
 QWidget *wxWindowQt::QtGetClientWidget() const
 {
+    auto frame = wxDynamicCast(this, wxFrame);
+    if ( frame )
+        return frame->GetQMainWindow()->centralWidget();
+
     return wxQtGetDrawingWidget(m_qtContainer, GetHandle());
 }
 
@@ -1086,6 +1121,24 @@ void wxWindowQt::DoSetClientSize(int width, int height)
     }
 }
 
+wxSize wxWindowQt::DoGetBestSize() const
+{
+    const wxSize size = wxWindowBase::DoGetBestSize();
+
+    if ( dynamic_cast<wxQtWidget*>(GetHandle()) )
+    {
+        return size;
+    }
+
+    wxSize bestSize = wxQtGetBestSize( GetHandle() );
+    if ( size.IsFullySpecified() )
+    {
+        bestSize.IncTo(size);
+    }
+
+    return bestSize;
+}
+
 void wxWindowQt::DoMoveWindow(int x, int y, int width, int height)
 {
     QWidget *qtWidget = GetHandle();