CODEWITHSUNDEEP
arrayslisttreeviewgtk3vala
Néstor A.C.
Néstor A.C.

Reputation: 1

error: `Gtk.TreeIter' is not a supported generic type argument

I want to move some selected items between trees in Gtk+3 with Vala. The problem is that I cannot create a list to include all the item iterations that have to be removed, after adding them to the second tree (if I remove them just after adding them, only half of the selected items are correctly removed). It seems that Gtk.TreeIter is not a type, so I cannot make a list from it. If you need the complete code, I can happily publish it (just 109 lines of code), it's floss. Thank you.

valac --pkg gtk+-3.0 --pkg gee-0.8 treeview-prueba.vala
treeview-prueba.vala:75.23-75.34: error: `Gtk.TreeIter' is not a supported generic type argument, use `?' to box value types
   75 |             GLib.List<Gtk.TreeIter> iter_list_to_remove;
      |                       ^~~~~~~~~~~~                      
treeview-prueba.vala:87.17-87.39: error: The name `add' does not exist in the context of `GLib.List<Gtk.TreeIter>?' (glib-2.0)
   87 |                 iter_list_to_remove.add(itera2);
      |                 ^~~~~~~~~~~~~~~~~~~~~~~         
Compilation failed: 2 error(s), 0 warning(s)
make: *** [makefile:2: all] Error 1

The relevant code is:

delete_button.clicked.connect (() => {
    var selection = view.get_selection ();
    Value s= Value (typeof (string));
    Gtk.TreeModel model;
    Gtk.TreeIter itera;
    Gtk.TreeIter itera2;
    var selected_rows = selection.get_selected_rows(out model).data;
    GLib.List<Gtk.TreeIter> iter_list_to_remove;
    for (int i = 0; i<selection.count_selected_rows() ; i++) {
        s="hola";
        list_store.get_iter(out itera,selected_rows);
        while (!selection.iter_is_selected (itera) ) {
            list_store.get_iter(out itera,selected_rows);
            selected_rows.next();
        }
        list_store.get_value(itera,0,out s);
        stdout.printf( " %s ",s.get_string());
        list_store2.append (out itera2);
        list_store2.set (itera2,0,s.get_string());
        iter_list_to_remove.add(itera2);
        selected_rows.next();
    }
    foreach (var iteration in iter_list_to_remove){
        list_store.remove(ref iteration);
        }
});

I expected that it compiled correctly, but I get the above error.

Upvotes: 0

Views: 23

Answers (1)

nemequ
nemequ

Reputation: 17522

Change GLib.List<Gtk.TreeIter> to GLib.List<Gtk.TreeIter>.

This is really a consequence of how generics are implemented in Vala, which reflects how these APIs are implemented in C. If you're not familiar with C (or a similar language) this may be a bit difficult to follow, sorry! Basically, at the C level the API for a "generic" function is implemented using an argument of type gpointer, which is just a typedef to void*. In other words, whatever value you pass there must fit inside of a pointer.

GtkTreeIter (the C type) is typically passed as a value, not a reference, so for APIs like this what you really need to do is pass a pointer (i.e., a GtkTreeIter* instead of a GtkTreeIter). The best way to get Vala to do that is to mark it as nullable (GtkTreeIter?). Technically you could also use a pointer in Vala, but to be perfectly honest you should almost never use pointers in Vala; you're basically opting out of memory management. Making it nullable makes Vala pass the argument as a pointer at the C level, but Vala will still handle the memory management for you.

Upvotes: 0

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