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On 9/2/21 6:38 PM, Bill Spitzak wrote:
It does seem like a bug, calling value() should not
have any side-effects. Especially because the tabs widget works
even if nobody calls value().
I think the problem here is with value(Fl_Widget*) which changes
the current tab.
What I've found is when you click on a tab, the
Fl_Tabs::handle()
changes the value of the tab using value(Fl_Widget*), which sets
the new value, and returns 1 if it was changed or 0 if not.
And based on that return value, handle() invokes do_callback()
if a change was made.
The problem is the value(Fl_Widget*) method is improperly
returning
0 even though the tab was indeed changed.
This is because the logic in Fl_Tabs::value(Fl_Widget*) to
detect a change
assumes it can walk the loop calling hide() and show() on the
children,
and can check the visible() of the new tab as a way to detect if
there was
a change.
The problem is when the loop calls hide() to deselect the first
child, "Tab A",
this single call to hide()..
1. Sends "Tab A" an FL_HIDE event -- OK
2. Sends "Tab C" an FL_SHOW event -- THIS
HERE IS THE PROBLEM
3. Sends "Tab C" an FL_FOCUS event
Step #2 causes Tab C to be shown before the loop expects it
to be,
and this confuses the loop's logic to detect that a change was
made.
Assuming that the above hide() event behavior is not a bug, this
can
I think be fixed/avoided by rewriting the value(Fl_Widget*) code
this way:
int Fl_Tabs::value(Fl_Widget *newvalue) {
+ Fl_Widget *oldvalue = value();
Fl_Widget*const* a = array();
- int ret = 0;
for (int i=children(); i--;) {
Fl_Widget* o = *a++;
if (o == newvalue) {
- if (!o->visible()) ret = 1;
o->show();
} else {
o->hide();
}
}
- return ret;
+ return oldvalue != newvalue ? 1 :
0; // change detected
}
The only problem with that, and I think is the reason the code
is the way it is,
is that call to value() is non-trivial; it goes thru a loop just
to find the current value(),
so perhaps it was an efficiency call.
But there really cant be very many tabs; there's a visual limit
to how many
there can be, so perhaps efficiency here is unwarranted.
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