ComboBox is gtk-rs

I am trying to create a ComboBox in rust using gtk-rs, but it is not showing any text. The space, however is being allocated in the ComboBox. Can anybody tell me what I am doing wrong here?

let model_store =  gtk::ListStore::new(&[gtk::Type::String]);
model_store.insert_with_values(None, &[0], &[&"String1"]);
model_store.insert_with_values(None, &[0], &[&"String2"]);
model_store.insert_with_values(None, &[0], &[&"String3"]);
model_store.insert_with_values(None, &[0], &[&"String4"]);
let combobox = gtk::ComboBox::new ();
combobox.set_model(Some(&model_store));

For gtk-rs they have a gitter channel and I'd recommend you ask this question there as it's very specific.

Additionally they have a whole repository of examples and you should search it for combobox examples which might help you solve your problem.