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How can I interact with target the widget from a drop event

I'm trying to update a ListBox widget after dropping some files on it.

This is the relevant part of my current code:

```rust
fn on_file_drop(target: &DropTarget,
                value: &Value,
                _x: f64,
                _y: f64) -> bool {
    if let Ok(file_list) = value.get::<FileList>() {
        let list_box = target.widget().unwrap();
        //  ^^^^^^^^ this becomes a Gtk::Widget instead of Gtk::ListBox
        
        for file in file_list.files() {
            let basename = file.basename();
            let path = file.path();
            println!("{path:?} {basename:?}");
        }
        return true
    }
    false
}

fn build_ui(app: &Application) {
    // more UI

    let files_list = ListBox::builder()
        .width_request(200)
        .height_request(300)
        .build();
    let files_drop_target = DropTarget::builder()
        .actions(DragAction::COPY)
        .build();
    files_drop_target.set_types(&[FileList::static_type()]);
    files_drop_target.connect_drop(on_file_drop);
    files_list.add_controller(files_drop_target);

    // more UI
}
```

The problem is, that I don't understand (and can't find anything concrete in [documentation](https://docs.gtk.org/gtk4/class.DropTarget.html) or examples) on how to interact with the widget that is associated with the DropTarget.

When I try to explicitly convert the widget to a ListBox like this I get an error:

```rust
let list_box: ListBox = target.widget().unwrap().into();
```

> the trait bound `gtk4::ListBox: From<gtk4::Widget>` is not satisfied required for `gtk4::Widget` to implement `Into<gtk4::ListBox>`

I can't implement this example: https://github.com/gtk-rs/examples4/blob/master/src/bin/drag_and_drop.rs, the functions `.drag_dest_set()` and `.connect_drag_data_received()` don't even exist on my instanciated widgets.

How can I get a ListBox out of the `target` argument, so I can interact with it? Or would I make my life much easier by implementing everything in a struct instead of just plain functions?