How to create array of object instances in vala - arrays

Question

as I was trying to nail down the bug why my gtk4_list_clocks only ever update one of the clocks and not all of them, I've traced down the problem to be in GLib.SList.prepend().
Changing from GLib.SList to Gee.ArrayList didn't solve the problem.
In the c code example a list of all clock widgets were created by appending them to a singly linked list. I've tried to mimic that but as it turned out the list size is always 1 and only one object ever get appended.
/* This is the list of all the ticking clocks */
static Gee.ArrayList<Clock> ticking_clocks = null;
// ...
construct {
ticking_clocks = new Gee.ArrayList<Clock> ();
}
void start_ticking () {
/* if no clock is ticking yet, start */
if (ticking_clock_id == 0) {
ticking_clock_id = GLib.Timeout.add_seconds (1, tick);
}
ticking_clocks.add (this); // Bug
// Although instance pointer is different according to the number of instantiated objects!!!
print ("Clock instance %p\n", this);
// always 1 !!!
print ("Number of ticking clocks %d\n", ticking_clocks.size);
}
Could somebody please help to point out the problem?
Thanks in advance.

Answer 1

This works:
void main () {
var a = new SList<Clock> ();
a.append (new Clock ());
a.append (new Clock ());
a.append (new Clock ());
a.append (new Clock ());
a.append (new Clock ());
print (#"Array length is $(a.length())\n");
}
class Clock {}
I'm not sure what the problem would be in your code, but I would remove the static from the ticking_clocks field. It can also be initialised with:
private Gee.ArrayList<Clock> ticking_clocks = new Gee.ArrayList<Clock> ();
I would also move the ticker outside the instance. If your SourceFunc returns Source.CONTINUE it will carry on ticking. Here is a stripped back example using MainContext. MainContext is the event loop within GLib's MainLoop, GApplication, etc. It is useful to understand to get a good grasp of Vala's async functions/methods:
void main () {
var maincontext = MainContext.default();
var time_to_quit = false;
var count = 5;
SourceFunc quit = () => {
print (#"$count\n");
count --;
var result = Source.CONTINUE;
if (count < 1) {
time_to_quit = true;
result = Source.REMOVE;
}
return result;
};
Timeout.add_seconds (1, (owned)quit);
while (time_to_quit == false) {
maincontext.iteration( true );
}
}
Be aware the Timeout is not precise, it is at least a second. So you may want to increase the frequency and then check the time when you update the clock.