Stan wrote:
> [..]
>> > What is often lost in this discussion is the fact that
>> > begin(); new Thing(..); new Thing(); end()
>> > is NOT exactly the same as
>> > add(new Thing(..)); add(new Thing(..));
>>
>> I'm probably forgetting something about FLTK2; what's the difference?
>
> I've never used fltk2. In the context of fltk1:
>
> // Example 1
> Fl_Group* g = new Fl_Group(..) // implicit begin()
> g->end();
> g->add(new X(..)) // adds an X* to g
>
> // Example 2
> Fl_Group* g = new Fl_Group(..) // implicit begin()
> new X(...) // adds all widgets created by the execution of
> // X::X() to Fl_Group::current()
> g->end()
There are further differences: g->end() sets the *global* Fl_Group::current_
pointer to g->parent(), and this can change the global "adding situation",
whereat g->add() doesn't. Assume, I have a group MyGroup with an extra_add()
method coded like that:
void MyGroup::extra_add() {
begin()
new Fl_Button(...);
new Fl_Box(...); etc.
end(); // --> Fl_Group::current_ =
} this->parent()
and now the following usage of extra_add():
int main()
{
Fl_Window* win1;
MyGroup* g;
win1 = new Fl_Window(...); // --> Fl_Group::current_ = win1
g = new MyGroup(...);
g->end();
win1->end(); // --> Fl_Group::current_ = 0
if( something )
g->extra_add(); // --> Fl_Group::current_ = win1
Fl_Window* win2 = new Fl_Window(...);
....
}
If 'something' is false, win2 becomes a top level window, because at its
construction moment Fl_Group::current_ was 0, but if 'something' is true,
win2 becomes a sub-window of win1, what was probably not intended.
A save way would be using add() instead of begin()/end() in extra_add().
Unfortunately, add() has also a disadvantage, namely in situations where
the global Fl_Group::current_ pointer is *not* 0. The call
g->add( new SomeWidget(...) );
adds the new constructed widget then nevertheless at first to the current
open group (the wrong group), and g->add() must move it following from
there to g. This can imply a wasted reallocation of the children array of
the wrong group.
An effective *and* save way of extra_add() leaving the global environment
unchanged should be
void MyGroup::extra_add()
{
Fl_Group* previous = Fl_Group::current();
begin(); // Fl_Group::current_ = this
new Fl_Button(...); // adds immediately to 'this'
....
Fl_Group::current (previous); // Restore previous open group
// (instead of end())
}
Hartmut
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