Method add

src/elements/element.rs:530–553

(&self, child: &dyn Element)

    }

    fn add(&self, child: &dyn Element) {
        let mut comp = self.as_ref().borrow_mut();

        assert!(
            !comp.destroyed,
            "Widget was already destroyed but is being interacted with"
        );

        if let Some(parent) = child.parent() {
            parent.remove(child.id());

            if parent.id() != self.id() {
                comp.children.push(child.id());
                child.set_parent(Some(self.id()));
                if comp.onchildadd.is_some() {
                    let _ = comp.onchildadd.get().try_send(child.id());
                }
            }

            if let Some(widget) = comp.canvas.as_ref() {
                widget.sync_depth();
            }
        }
    }

    /// The child must be sure that his parent reference is correct.
    /// The child must remove the parent reference by himself: child.set_parent(None);