Vala. How do you delete all the children of a GTK container?

Question

Solved. See the reply for examples.

I have a container with children. I need to delete all the children. This is easy in C. Vala does not work.

The following code produces an error missing type argument for collection.

var a_box = new Box (Orientation.VERTICAL, 0);
// Add some children
List children = a_box.get_children();
foreach (Widget element in children) { }

I tested over twenty variations of this code plus with many data types. When I do not get the missing type complaint, I end up with a data type that cannot be used as a widget which means I cannot destroy it.

Using Vala, not C or Python or any of the many languages where this is easy, how do you remove all the children of a container?

From what I can see, the only way to get the children is as a List but in Vala a List entry cannot be used to remove or destroy widgets.

Both remove and destroy work in C. I have several C based applications doing both. The Vala 0.30 compiler rejected every translation from C to Vala and refused to compile examples from Valadocs etc.

Christychristye

Re: examples from valadoc, can you provide any specific examples? I'm sure Florian would like to know about any broken examples… – Parenteau

@nemequ, I expanded the bit about Valadocs and other sources. Valadocs needs something like the PHP comments where people can provide and discuss examples of usage. – Christychristye

Answer 1

To correct the error about missing type arguments, just provide the type arguments. The signature for Gtk.Container.get_children() says the type is List<weak Widget>, so let's use that:

GLib.List<weak Gtk.Widget> children = container.get_children ();
foreach (Gtk.Widget element in children)
  container.remove (element);

Of course, you could also just use type inferencing:

var children = container.get_children ();
foreach (Gtk.Widget element in children)
  container.remove (element);

Or even just avoid the temporary variable altogether:

foreach (Gtk.Widget element in container.get_children ())
  container.remove (element);

But the easiest way I can think of would be:

container.foreach ((element) => container.remove (element));

Parenteau

Originall I tried variations on "var children =" but the compiler or the execution complained about type incompatibilities. I did not keep copies of the failed examples. I added printf in an attempt to find out what was available in the loop. Again there were type incompatibilities. I will go back and test again. For a later development of this code, I will need to know if it is a box or grid, etc, to report on what is deleted. – Christychristye

The .forall description says it deletes things internal to the container object. This suggests that for some container types .forall will delete too much. .forall works for a box. I expect grid and similar containers may fail after .forall. I did not find documentation of which containers will fail. I will stick with the versions using .get_children. – Christychristye

Actually, I think it will work as expected for a grid. I believe what it is referring to are widgets which add intermediaries between your widget and themselves; for example, Gtk.ListBox will automatically create a Gtk.ListBoxRow to hold your widget. forall will invoke the callback on the Gtk.ListBoxRow, but get_children will also return the Gtk.ListBoxRow, so it doesn't really matter… you just need to be aware of what is going on in both cases. – Parenteau

End-users should not use .forall() as they should only manipulate their own widgets, and let the Container delete any of its internal, implementation-detail widgets. The correct way to loop over widgets in non-implementation code is .foreach(). Unless you know you need .forall(), it should not be used, and usually as a user of the widget you don't really need it (and if you think you need it, you probably have a larger problem and/or a bad design). – Feminine