Re: Please help (core dump)

On 2020-07-25 17:35, Carlo Wood wrote:
> Why would this core dump??
>
> LinuxChessboardWidget is defined as:
>
> class LinuxChessboardWidget : public cwmm::ChessPositionWidget, public Gio::ActionMap
> {
>    ...
>
> I have to derive from Gio::ActionMap because its constructor is protected.
> The call to `add_action` above is to that class.
>
> Can someone tell me what I'm doing wrong?
>
> Carlo
>
Gio::ActionMap is an interface. That's why its constructor is protected. 
An interface can't be instantiated by itself. It must be implemented by 
a class which can be instantiated. If you really must implement 
Gio::ActionMap in your class (which I doubt), there is one or (probably) 
two errors.

First, interfaces must come before the widget class in the list of base 
classes.

class LinuxChessboardWidget : public Gio::ActionMap, public cwmm::ChessPositionWidget

This is opposite to what's done in gtkmm's classes that wrap gtk classes.

Second, your constructor must call a special Glib::ObjectBase constructor that registers your class with its own GType in glib's GType system. For instance

LinuxChessboardWidget(......) : Glib::ObjectBase("myWidgetClass") ..... // Or whatever you want to call it.

This is an unusual way of using Gio::ActionMap. I don't know if these are the only necessary changes. Much more common is to use one of the classes that already implement Gio::ActionMap: Gio::SimpleActionGroup, Gtk::Application (via Gio::Application) or Gtk::ApplicationWindow.

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