On Monday, September 26, 2022 at 9:06:44 AM UTC-4 Albrecht Schlosser wrote:

On 9/26/22 14:08 Pierre Rouleau wrote:

On Monday, September 26, 2022 at 4:14:25 AM UTC-4 Manolo wrote:

Hi Pierre,

Hi Manolo, thanks for the answer.

 

One key information is that the destructor of an Fl_Group also deletes all the group's children :

 see https://www.fltk.org/doc-1.3/classFl__Group.html#a9a71aac1ca586825ff0c790f8f99f9cf

Now, because FLTK widgets are placed in Fl_Window's and Fl_Window's are Fl_Group's,

when a window is deleted, all the widgets it contains are deleted too.

Ok, but if you have code that creates a pointer to a FL_button with new, like the following, don't you have to register that FL_Button somewhere so that it is know as a member?  Is the new operator overridden by FLTK?

        Fl_Button *fluidButton = new Fl_Button(25, 80, 70, 50, "button2");

No, the new operator is not overridden by FLTK, and yes, you need to register the button as a child of its parent group. But this is usually done automatically.

Every FLTK container widget (derived from Fl_Group) calls `begin()` in its constructor. This registers it as the "current group". If you create a new widget like in your code above, the constructor of that widget "registers" it as a child of the "current group" by calling something like `Fl_Group::current()->add(this);` i.e. the new widget adds itself to the "current group" as a child widget. This is necessary to handle events and draw the children of the container anyway.

A very simple example is test/hello.cxx which creates a window and a button that is implicitly added to the window. If you look at the code you will also see `window->end();` before the window is shown to disable further automatic adding of widgets to this Fl_Window (Fl_Group).

Of course you can also disable this automatism and add/remove widgets to Fl_Group widgets explicitly, but this is another story.

Ahhhh.  That make sense.  Thank you!! 

One more question: if the contractor does not call the end member function, does this mean that the 'automatic' registration of widgets continue to operate inside calls to other member function of that class?