main.rs

use gtk::prelude::*;
use gtk::{glib, Application, ApplicationWindow, HeaderBar, Box, Orientation, Button, FlowBox, Label};

const APP_ID: &str = "BoxSizing";

fn main() -> glib::ExitCode {

    let app = Application::builder().application_id(APP_ID).build();
    app.connect_activate(build_ui);
    app.run()
}

fn build_ui(app: &Application) {
    let window = ApplicationWindow::new(app);
    window.set_default_size(640, 480);

    let vbox = Box::new(Orientation::Vertical, 0);

    let btn = Button::new();
    btn.set_label("Add child to flowbox");
    
    let flow = FlowBox::new();

    vbox.append(&btn);
    vbox.append(&flow);

    btn.connect_clicked(move |b| {
        let bx = Box::new(Orientation::Vertical, 0);
        let b = Button::new();
        b.set_label("child");
        bx.append(&b);
        flow.append(&bx);
    });
    
    window.set_child(Some(&vbox));
    
    window.present();
}

Screencast.from.2023-11-25.14-04-53.webm