Hook up to signal

src/main.rs

@@ -1,5 +1,5 @@
 use gtk::prelude::*;
-use gtk::{Application, ApplicationWindow};
+use gtk::{Application, ApplicationWindow, Button};
 
 const APP_ID: &'static str = "org.gtk-rs.Gamarjoba";
 
@@ -10,9 +10,23 @@ fn main() {
 }
 
 fn build_ui(app: &Application) {
+
+    let button = Button::builder()
+        .label("Hit me!")
+        .margin_top(12)
+        .margin_bottom(12)
+        .margin_start(12)
+        .margin_end(12)
+        .build();
+
+    button.connect_clicked(move |button| {
+        button.set_label("Hahaha! Gay!");
+    });
+
     let window = ApplicationWindow::builder()
         .application(app)
         .title("Gamarjoba from GTK4")
+        .child(&button)
         .build();
 
     window.present();