Re: Deriving from Pango::Layout

[Kjell Ahlstedt <kjell ahlstedt bredband net>]

Den 2017-02-17 kl. 21:14, skrev Phil Wolff:
> #include <gtkmm.h>
>
> class CTextBuffer : public Gtk::TextBuffer
> {
> public:
>     static Glib::RefPtr<CTextBuffer > create ( Gtk::TextView* );
>     virtual ~CTextBuffer () {}
> private:
>     explicit CTextBuffer ( Gtk::TextView* );
>     Gtk::TextView* m_pTextView;
> };
> //==================================
> Glib::RefPtr<CTextBuffer > CTextBuffer::create ( Gtk::TextView* pView )
> {
>     return Glib::RefPtr<CTextBuffer > ( new CTextBuffer ( pView ) );
> }
>
> CTextBuffer::CTextBuffer ( Gtk::TextView* pView )
> {
>     m_pTextView = pView;
> }
>
> The example above compiles with no errors. However when I try it with 
> Pango::Layout in place of Gtk::TextBuffer:
>
> #include <gtkmm.h>
> #include <pangomm.h>
>
> class CLayout : public Pango::Layout
> {
> public:
>     static Glib::RefPtr<CLayout > create ( const 
> Glib::RefPtr<Pango::Context >& );
>     virtual ~CLayout () {}
> private:
>     explicit CLayout ( const Glib::RefPtr<Pango::Context >& );
>     Glib::RefPtr<Pango::Context > m_refContext;
> };
> //==================================
> Glib::RefPtr<CLayout > CLayout::create ( const 
> Glib::RefPtr<Pango::Context >& context )
> {
>     return Glib::RefPtr<CLayout > ( new CLayout ( context ) );
> }
>
> CLayout::CLayout ( const Glib::RefPtr<Pango::Context >& context )
> {
>     m_refContext = context;
> }
>
> pl.cc: In constructor ‘CLayout::CLayout(const 
> Glib::RefPtr<Pango::Context>&)’:
> pl.cc:20:65: error: no matching function for call to 
> ‘Pango::Layout::Layout()’
>  CLayout::CLayout ( const Glib::RefPtr<Pango::Context >& context )
>                                                                  ^
> In file included from /usr/include/gtkmm-3.0/gtkmm/widget.h:32:0,
>                  from /usr/include/gtkmm-3.0/gtkmm/action.h:31,
>                  from /usr/include/gtkmm-3.0/gtkmm/toggleaction.h:27,
>                  from /usr/include/gtkmm-3.0/gtkmm.h:95,
>                  from pl.cc:1:
> /usr/include/pangomm-1.4/pangomm/layout.h:259:12: note: candidate: 
> Pango::Layout::Layout(const Glib::RefPtr<Pango::Context>&)
>    explicit Layout(const Glib::RefPtr<Context>& context);
>             ^~~~~~
> /usr/include/pangomm-1.4/pangomm/layout.h:259:12: note: candidate 
> expects 1 argument, 0 provided
>
> Can someone give me a clue as to what I'm failing to see?
The constructor CLayout ( const Glib::RefPtr<Pango::Context >& ) 
implicitly calls the default constructor of the base class, 
Pango::Layout::Layout(). But Pango::Layout does not have a default 
constructor.